Rough running

[Billy Mild]

Let me preface this post with the dilemma I'm in, daily driver Jeep CRD is out of commission due to a trusted out diesel tank, 2 motorcycles are out of service 1 with a seized engine and the other cosmetic issues, and now the Vette has decided to run a little rough.

On the highway the ZR1 seemed to almost fight against itself, but if I go full throttle the Lt5 pulls just fine. The car would buck or almost feel like it was going to die but if I have the car more throttle it would pull without hesitation.

It is happening at low rpm sub 3000 RPM. Something that I also noticed is that the speedo quits working randomly.

Could this be a fuel pump problem? Spark plug issue?

Fuel injectors, coil packs, and wires have been replaced in the last 2 years. I have SW headers and new O2 sensors with a Marc Haibeck tuned chip.

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[BigJohn]

Let me preface this post with the dilemma I'm in, daily driver Jeep CRD is out of commission due to a trusted out diesel tank, 2 motorcycles are out of service 1 with a seized engine and the other cosmetic issues, and now the Vette has decided to run a little rough.

On the highway the ZR1 seemed to almost fight against itself, but if I go full throttle the Lt5 pulls just fine. The car would buck or almost feel like it was going to die but if I have the car more throttle it would pull without hesitation.

It is happening at low rpm sub 3000 RPM. Something that I also noticed is that the speedo quits working randomly.

Could this be a fuel pump problem? Spark plug issue?

Fuel injectors, coil packs, and wires have been replaced in the last 2 years. I have SW headers and new O2 sensors with a Marc Haibeck tuned chip.

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So I'm not the only one who has issues with multiple vehicles.

[8cam]

You might not like this answer, but those symptoms sound exactly like an ECM going out. I had similar issues and finally rolled the dice on a repair, which worked in my case. But sometimes they don't.

[Billy Mild]

Is there a ECU repair service? This was a common problem on the old 944's I had. There were a few places that actually re did all the solder joints, fixed the problem.

Did your car seem to pull clean for full throttle?

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[Billy Mild]

http://www.zr1.net/forum/showthread.php?t=25548

I found this old thread and they talk about having it rebuilt or a possible new option. Sounds like MegaSquirt makes a new ECM that is plug and play. I would like to figure out cost and if it has all the same functionality as stock now.

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[8cam]

I had mine repaired by K&B Corvette here in Atlanta. He said he had about a 2/3 success rate with them. I knew mine was tha culprit so I rolled the dice and the repair worked. Yes the symptoms were the same, rough idle and running. Part throttle acceleration was ok, full throttle was ok at first. Then it wasn't, and things just got worse. Definitely worth checking it out. I eliminated all other possibilities before I was certain it was the ECM, finally swapped in a known good one to confirm it.

[Billy Mild]

My idle seems okay. Not bad at all. Reving the engine while stopped seems fine as well.

What tests did you do?

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[Paul Workman]

It might well be the ECM, and you may be right. But, it sounds like a "closed loop" situation (to me).

Just a suggestion: B-4 throwing another part at it, or ASSUMING those parts you've recently replaced "can't possibly" be bad, do have it scanned and see what is going on before trying to second-guess it further. It might be something simple...or it could be the ECM. But, odds are it will be something else - like a connector?. Just sayin.

:cheers:

[Billy Mild]

It might well be the ECM, and you may be right. But, it sounds like a "closed loop" situation (to me).

Just a suggestion: B-4 throwing another part at it, or ASSUMING those parts you've recently replaced "can't possibly" be bad, do have it scanned and see what is going on before trying to second-guess it further. It might be something simple...or it could be the ECM. But, odds are it will be something else - like a connector?. Just sayin.

:cheers:
I'm all for testing. I already own a MT2500 scanner. I don't know what I would be doing to check the ECU.

I was thinking a possible fuel pump issue, but I don't have a fuel pressure gauge to test with. I may pick one up this weekend.

The car when it has this issue acts like my RZ350 when the carbs are out of sync. The cylinders run at different speeds and fight each other

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[8cam]

I have the shop manual and basically just started working through all the rough running tests. It's pretty comprehensive and gives you expected results throughout. After testing everything, the only item left for me was the ECM. I borrowed one from Russ and my car suddenly ran perfectly, so it was clear what the issue was. The guy at K&B isn't very sociable, but for me at least, the fix was great. He told me that they will all fail at some point, and with a 2/3 success rate on repairs, they will only keep getting more expensive. Hopefully your issue is something simple, but definitely start working through the shop manual.

[Billy Mild]

Wife drove the car today. She said that it was almost bucking when in traffic today. She mentioned this on the drive back from work. She noticed it at highway speeds.

It has been the hottest its ever been the past few days. I wonder if that has anything to do with it at all. I also thought maybe my air duct is getting too soft and collapsing.

I will start working through the troubleshooting guide in the Shop Manual. 8cam do you have a page that you started with?

[BigJohn]

It's been a hot week; is the car running hotter than normal?

[Billy Mild]

The car is running right in the middle of the gauge. I have a haibeck tune so that probably helps.

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[Billy Mild]

Threw the scanner on it this morning. The car was bucking 2 minutes after leaving my driveway. If at any time I open the throttle close to full throttle it smoothes out.

I noticed my IAC counts are higher than normal and the BLM counts seem a bit off. I pulled over and unplugged the IAC and the idle was really high like 2000 rpm. I shut the engine off and plugged it back in. The idle was normal but the IAC counts were still high.

5422

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[Billy Mild]

Would a bad IAC cause rough running at all?

Should I try reseating all the ECU connectors and chip before doing any other troubleshooting?

[Billy Mild]

I drove the car this morning after giving it a full weekend break. The car ran smooth as ever and had 0 issues on the way to work. I'm starting to think it has to do with outside temp and when the engine is warmed up.

This leads me to believe it is an electrical issue.

[Billy Mild]

After work the car ran rough intermittently. The only thing I can see is the BLM is way off between the right and left side. Also the IAC counts are higher than normal.

At this point I'm thinking O2 sensors (Standard Brand), ECU, or IAC would be bad. The O2 sensors could possible cause these kinds of issues.

Any ideas?

[Billy Mild]

It was even worse today on the way to work. At this point I am honestly considering selling the F'ing thing. Nothing really seems out of whack.

Does anyone have a spare ECU without a chip that I could borrow and swap in to see if that alleviates all my problems??

[Paul Workman]

Intermittent issues are the worst. I had a similar issue with my 95 LT1 car; took it to the shop, only to have them say: "No problem found". But, before I reached home, the rough running cropped up again.

That issue is what prompted me to buy a scanner and do datalogging on the fly. That's when I found one of the O2s was shorting out, intermittently, causing the ECM to flood that side of the motor with fuel. BLM on that side went nuts too - along with injector dwell time on that one side.

Point is, if you can datalog in real time, you might be able to catch what is going on. Mind you, often it didn't throw a code either.

But, have patience. Once you have your "Ah-HA!" moment, all this trouble will fade away to be forgotten. Trust me. (I've been there, done that several times!!).

:cheers:

Paul.

[2ljd]

Paul,

If you don't mind me asking, what scanner/program did you get?

[rush91]

"Threw the scanner on it this morning. The car was bucking 2 minutes after leaving my driveway. If at any time I open the throttle close to full throttle it smoothes out"


What do you mean by bucking? I only ask because I hear that term a lot on here. What I'm picturing is the car is jerking or bucking, kinda like the fuel is being cut off? Does this happen when you let off the gas or are into the gas? Any gear? I saw you mentioned it happened mostly under 3000RPM........

[Paul Workman]

Paul,

If you don't mind me asking, what scanner/program did you get?

Mine is a discontinued AutoXray unit - for which I also was able to purchase the computer program which produces graphs and charts from the data registered in the unit.

I believe AutoXray is "no more". I also purchased a Snap-On MT 2500 "in case" the AX dies. However, I need to also buy the appropriate cartridges to read OBD-1 duties.

[tomcat]

Hi, have you checked your coil packs or vaccum hoses?
Manfred E....:proud:
91 blk/blk #906

[Billy Mild]

Intermittent issues are the worst. I had a similar issue with my 95 LT1 car; took it to the shop, only to have them say: "No problem found". But, before I reached home, the rough running cropped up again.

That issue is what prompted me to buy a scanner and do datalogging on the fly. That's when I found one of the O2s was shorting out, intermittently, causing the ECM to flood that side of the motor with fuel. BLM on that side went nuts too - along with injector dwell time on that one side.

Point is, if you can datalog in real time, you might be able to catch what is going on. Mind you, often it didn't throw a code either.

But, have patience. Once you have your "Ah-HA!" moment, all this trouble will fade away to be forgotten. Trust me. (I've been there, done that several times!!).

:cheers:

Paul.

I have been driving with my MT2500 on it most of the time. The only thing I can find is BLM is way off between the left and right side, and my O2 sensor seems to sometimes hang for a second, then go right back to normal(which is all over the place), my IAC counts are occasionally too high.

"Threw the scanner on it this morning. The car was bucking 2 minutes after leaving my driveway. If at any time I open the throttle close to full throttle it smoothes out"


What do you mean by bucking? I only ask because I hear that term a lot on here. What I'm picturing is the car is jerking or bucking, kinda like the fuel is being cut off? Does this happen when you let off the gas or are into the gas? Any gear? I saw you mentioned it happened mostly under 3000RPM........

Bucking or cutting out. This morning it was so bad the car kind of shut off then came back to life. Its like the car lost power that time. Most of the time it feels as if the banks of the motor is fighting itself, but if I go WOT it clears up. This happens with the KEY ON or OFF.

Hi, have you checked your coil packs or vaccum hoses?
Manfred E....:proud:
91 blk/blk #906

Is there a way to check the coil packs WITHOUT pulling the plenum? I have been trying to find something in the FSM.

I will give a brief history on the car. When I purchased it the car did not run well. It had a few stumbles and didn't run clean. Another member and I went through and replaced all the fuel injectors, spark plugs, and wires. Along with that I cleaned all the grounds. Fixed a lot of small vacuum leaks. Replaced fuel filter. This was 2 years ago.

Last year I replaced all the coil packs, and had to re-fix a few vacuum leaks. I have ran a few tanks of seafoam as well in the gas. No change.

This summer I have put on Longtube headers with Z06 cats, xpipe in the exhaust, new O2 sensors(Standard Motor brand), and a tune from Marc Haibeck. After I had these things done the car ran pretty dang well. It was smooth pulled great in any condition then out of no where I noticed it was running bad almost like it was sputtering when on the highway. That was last week and here I am with the same issue.

[Billy Mild]

I did some fuel pressure testing today. I bought an Actron Fuel pressure gauge. My results were FP1 static pressure with key on for a few seconds 44 PSI, FP2 with key on for a few seconds was 48 PSI on the dot. FP1 spiked to around 50 PSI then dropped down to 44 PSI. FP2 went to almost 52 PSI then dropped to 48 PSI. Would a clogged fuel filter cause a pressure difference?

I did the idle test with just FP1 and the pressure was right at 40-41 PSI.

It seems to bleed off after 10 or so seconds. The FSM says this is normal. I would still like to do the test for FPR test by jumping the 12v fuel pump test leads. I don't know where that jumper lead is located.

TL;DR- FP1 44 PSI, FP2 48 PSI for static fuel pressure test.

Is 44 PSI okay or should I go all anal and replace the fuel pump due to it not meeting the spec in the FSM?

[dredgeguy]

I had similar issues after taking my car to the GM steeler for A/C work. Car went to them perfect and came back bucking and stumbling. Check the throttle. Put a scanner on and press your gas pedal to the floor and see if it shows 100% throttle. When I did mine it was only showing 57% which messed everything up. Sometimes you need to adjust the throttle cable after pulling the plenum. That fixed my problem. Good luck and keep us posted.

[2ljd]

Mine is a discontinued AutoXray unit - for which I also was able to purchase the computer program which produces graphs and charts from the data registered in the unit.

I believe AutoXray is "no more". I also purchased a Snap-On MT 2500 "in case" the AX dies. However, I need to also buy the appropriate cartridges to read OBD-1 duties.

Cool, thanks!

[Paul Workman]

I did some fuel pressure testing today. I bought an Actron Fuel pressure gauge. My results were FP1 static pressure with key on for a few seconds 44 PSI, FP2 with key on for a few seconds was 48 PSI on the dot. FP1 spiked to around 50 PSI then dropped down to 44 PSI. FP2 went to almost 52 PSI then dropped to 48 PSI. Would a clogged fuel filter cause a pressure difference?

I did the idle test with just FP1 and the pressure was right at 40-41 PSI.

It seems to bleed off after 10 or so seconds. The FSM says this is normal. I would still like to do the test for FPR test by jumping the 12v fuel pump test leads. I don't know where that jumper lead is located.

TL;DR- FP1 44 PSI, FP2 48 PSI for static fuel pressure test.

Is 44 PSI okay or should I go all anal and replace the fuel pump due to it not meeting the spec in the FSM?

Fuel presure...

Under static (engine OFF) there should be no fuel flow, normally. So, even if a filter is severely blocked, static pressure will not be affected unless there is a total blockage - in which case the motor would not run at all, leave-alone at WOT.

Except for the bleeding off (so rapidly) the (static) pressure reading doesn't look out of line, after a couple seconds, after the key is turned to ON, engine OFF. Mine reads 43-44, and that seems to jive with most others when operating well.

After turning the key OFF, the pressure (I've read) should hold for several minutes, if all is well. Mine holds w/in 1# of when I turned the key off for over 10 minutes (long enough to see it wasn't leaking!).

Bleeding off after only 10 seconds...says to me either an injector(s) are leaking or the check valve in one or both of the pumps is leaking, OR the hose clamp in the tank is leaking. (I installed the worm (screw) type hose clamps on mine. Been good for 5 years now. I doubt this has anything to do with cutting out/jerking/misfire (aka "bucking"???) but I would schedule it for a "fix", IF I didn't seek to do so "on the spot".)

Dynamic fuel pressure test:

When fuel is flowing, AND should the filter be partially blocked, then pressure will suffer due to a bad, partially blocked filter. BTW, I replaced mine at 42xxx miles and was amazed at the amount of crud that came out of that filter. It is cheap and easy to change, and like an air filter you should just do it periodically, IMO.

Taping the fuel pressure gauge to the windshield and going for a drive (dynamic test):

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/FPtestLarge.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/FPtestLarge.jpg.html)

Cruising at 40 mph, the FP is hovering around 42-46#. Then, going WOT, the pressure jumps up to 53-55 for the duration of the WOT event, dropping back down to mid 40s again.

O2s...:

The O2 sensor output voltage continually cycles between high and low voltage, according to the exhaust gas pulses from each cylinder passing over it - or should at least. What you should be looking for are the "cross-count" numbers; the # of times the voltage reading switches from high to low. I don't have the exact figure, but it suffices to say they should be more or less symmetrical from left to right; also the BLMs should be "about equal" as well.

A "lazy O2 sensor will have significantly fewer "cross-counts, or the average will be significantly lower than than "normal" (if the average is hovering around the 300 or lower mV, the O2 is not working well. BTW, don't seal the wire harness where it enters the O2 sensor "for good measure". The sensor depends on atmospheric air sampling to make comparisons. IF dirt/grease or RTV sealant is closing off the opening to the atmosphere, the O2 can't work properly...ask me how I know:o.

The fact that it seems to run OK at WOT rules out stuff like the cam or crank position sensors. But, I'd want to rule out the MAP sensor. What does you scanner say re: the MAP readings?

Also, the Throttle Position Switch (TPS): It should be set at .5 VDC when closed. And, with the switch ON, engine OFF, the reading should increase smoothly through its entire arc - no drop outs! BTW, it isn't necessary to remove the TPS when removing the plenum. Simply lay the plenum on its back over the drivers' side (tire) w/ the throttle cables intact.

Spark plug reading:

Think of the spark plugs as data recorders: They will say volumes about fuel mix and ignition irregularities, if the misfiring is limited to one or two cylinders. If there is no clues to be had there, then that says something too!
ECM:

ECM: I'm not ready to suggest (yet) that exchanging ECMs is warranted, but as the other things are eliminated (by test verification when ever practicable - NOT, NOT, NOT by "it can't be this-or-that b/c that has been replaced", then the ECM is (of course) a common element. But, it might be worth running down a loaner, should it comes to it. Just a thought...

Oh! And, before testing further, clear the codes by removing power to the ECM for about a minute (should do it). Then, after it has been running (and misbehaving!), read the new codes. Also, know too that often a failing part can result/cause other seemingly un-related faults to occur. A bad O2 sensor will result in the injector dwell time on one side to be off, BLMs are affected by fuel delivery errors due to a bad O2 sensor...that kind of thing one has to keep in mind...

Frustrating, I know. But, too, as the circle spirals down, the issue is going to run out of hiding places. And, think of all the causal-related data you are learning along the way!:cheers:

[Billy Mild]

Where can I get an extension like shown in the pic for my FP gauge?

TPS was replaced earlier this year by Marc Haibeck and is set to .54 volts key on and engine off. Fuel filter was replaced 2 years ago.

The passenger side O2 sensor has an extension harness on it and had black wire loom on it that ended up getting melted. The wires were fine just the wire loom was melted. I put new wireloom on the wire as well as put heatshielding tape around it to prevent that from happening again.

I will throw the scanner on it again and check the CrossCounts. Those appears to be inline maybe 0 sometimes 1 for each side.

There is another ZR-1'er who has a NOS computer that he will let me borrow to rule out the ECU. If this was a 924/944 and I was having this issue I would point to FPR, and/or DME cold solder joints going bad.

[Paul Workman]

Where can I get an extension like shown in the pic for my FP gauge?

TPS was replaced earlier this year by Marc Haibeck and is set to .54 volts key on and engine off. Fuel filter was replaced 2 years ago.

The passenger side O2 sensor has an extension harness on it and had black wire loom on it that ended up getting melted. The wires were fine just the wire loom was melted. I put new wireloom on the wire as well as put heatshielding tape around it to prevent that from happening again.

I will throw the scanner on it again and check the CrossCounts. Those appears to be inline maybe 0 sometimes 1 for each side.

There is another ZR-1'er who has a NOS computer that he will let me borrow to rule out the ECU. If this was a 924/944 and I was having this issue I would point to FPR, and/or DME cold solder joints going bad.

Gotcha.

The cross-counts...I'll have to do some more research/comparison. But, zero and 1 are waaaay low - ordinarily. I can't rule out a test equipment data error (yet). I'll have to get back to ya on that.

The extension I got at Harbor Freight, believe it or not. But, I've seen them on ebay and AutoZone's site (once) too.

Can the MT 2500 be "que'd" so that it can capture events in a time frame? My datalogger will do that and is how I was able to zero in on the the intermittent cause by seeing the "before and after" data when the problem occurred.

Are we having fun yet???:dancing

[Billy Mild]

Gotcha.

The cross-counts...I'll have to do some more research/comparison. But, zero and 1 are waaaay low - ordinarily. I can't rule out a test equipment data error (yet). I'll have to get back to ya on that.

The extension I got at Harbor Freight, believe it or not. But, I've seen them on ebay and AutoZone's site (once) too.

Can the MT 2500 be "que'd" so that it can capture events in a time frame? My datalogger will do that and is how I was able to zero in on the the intermittent cause by seeing the "before and after" data when the problem occurred.

Are we having fun yet???:dancing

MT2500 does have a datalogger option that has a printer and you can capture "movie". I don't have manuals so it just is me poking around. I don't have the printer either.

Might be time to get ALDL droid and do some datalogging.

[Billy Mild]

I'm still waiting for my Bluetooth adapter for OBDI to do some true datalogging.

In the mean time I did some messing with the car. I swapped out the computer with an NOS example and went for a 45 minute drive. It seemed to run just fine. This could mean a few things.
1. The car only acts badly when its over 95 degrees out
2. The tune is off when its hot outside
3. The ECU is bad
4. Its something else all together

I was still getting weird BLM and INT numbers from my scanner when driving. Rarely was it close to 128 for BLM.

I decided to take a look at my spark plugs. Here are the pictures of my spark plugs. The plugs have 5000 miles on them. The gap was .045(which is not correct) and look to have some white powder on them. They are not black and sooty which is what I would expect from how the car has been running.

https://lh3.googleusercontent.com/FZlHWn08eQJsEkTj2N_ZjMt69lATF0bnehpu76E7zknVj0cs1T-5LcQ-uKzVdHiKPMnKosbitJvRtOadAcLDvSle7OcQIWYO5l1dTOO4gF ybNsnuoqSYwIIwijCP1Ahy-66HGoSyoV_An232J3UMAFOOpCNDYlNWqfcNeKVhAprz1r8eLs6 58AJmHUSiyruIBNBX2OJpNKbQy9c17QIBhaF8gGz_PErkrlLH5 uKljAoSUm8ASpIGen9QPxfHZk4DOE45YT1aiKgG3290QX2eXuC rlKzQeMguwEcCPi9Qp9XfoxAoYOYFm1VqMqV5gmeNwlL5hVRNu C15g_1TKpsCEEC-WqENi1p7dzAjIlUj9o-OqIV092Z9C1ayxcS_eha4vDxeIIu0PpZCR8uL6mbebV1dSuppK U02ka6imKuLq4eKHHdDxZrSA8boZ2XLJ4lJp8-GHGnlgx3fy1PbShO05NY5ecANysEi-RfjSXR-_nX2_D5TtPv2JRaHijZ3ITUSQJuwV0UXTolWmg-gXzK8C_tfHTbliv0FLBIiKgifo8FQofwuugLyBjjMxB-EXbKGHY6_B1ti94gaZd366x3bjnYple-lsmQ=w1289-h859-no
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After swapping out the plugs I went back to my ECU and went for a drive. It seemed to run fine except occasionally would stumble around the transition from before and after the secondaries would start opening. For example, coasting around 2700 rpm to a stop then mashing the throttle would cause a hiccup, or when going slow and stabbing the throttle it seemed to hiccup.

I am going to drive the car to work tomorrow and see how it does. If its bucking or not smooth then I will swap out the ECU again to see if that clears it up.

[Billy Mild]

Today the Vette seemed to run okay. It did die on my after coasting on an off ramp from the highway. I will still rolling so I pop started it.

Tomorrow is supposed to be hotter, maybe it will act up.

Could a bad IAC cause running issues below 3000 rpm?

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[Paul Workman]

Today the Vette seemed to run okay. It did die on my after coasting on an off ramp from the highway. I will still rolling so I pop started it.

Tomorrow is supposed to be hotter, maybe it will act up.

Could a bad IAC cause running issues below 3000 rpm?

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A couple of things are bugging me about your results:

The IAC counts...What are they?
The one BLM numbers...128 is nominal, WHAT IS THE OTHER BLM #s??
O2 counts: What ARE they - left and right?

In my experience, the FA mix has to be pig rich before it will stumble (misfire) like I think you're describing. The plug(s) would be either wet and smell of gasoline, or sooty black so as spark would be bridging through the carbon, rather than jump the gap. AND! Such a rich FA would result in hard starting, and once it does start, you'd be getting black soot blowing out of one or both exhausts. Whte-ish indicates LEAN, and lean will cause misfire (stumbling) w/o the black smoke! What say you?

BLM #s, or high IAC counts, don't necessarily mean either sensor is bad. But, rather the ECM's response to CLOSED LOOP readings that are out of whack, and it trying to compensate and correct it will result in sensor readings that are outside of the window.

LOW 02 cross-counts = a lazy sensor, and if O2 average voltage is LOW (lean) or high (rich) you can expect the injector dwell time to be opposite - the ECM trying to correct the AF ratio. (The kicker is that it may not throw a code - due to the nature of the problem (being randomly intermittent).

Divide and eliminate.For giggles, SWAP THE O2 positions (left one to the right, and visa-versa) and see if the BLM #s "swap sides". And, see if the O2 counts follow the O2 swap.

Gotta run...got a friend's sick 81 (C3) in the driveway, and he's here now to work on it.:cheers:

[Billy Mild]

The BLM numbers under WOT will be 128 on both sides. Sometimes under cruising the right side will be 116 BLM and the left side will be 126 BLM. What truly affects the BLM numbers?

The highest I have seen crosscounts is 4 or 5. Usually its around 0 or 1.

Today the temperature got up to 101 degrees. The car ran great all day. Occasionally when coasting to a stop right after pushing the clutch in the car would idle really low sub 500. It recovered everytime today, unlike yesterday where the engine died.

I will swap the O2 sensors maybe on Sunday.

[Paul Workman]

The BLM numbers under WOT will be 128 on both sides. Sometimes under cruising the right side will be 116 BLM and the left side will be 126 BLM. What truly affects the BLM numbers?

The highest I have seen crosscounts is 4 or 5. Usually its around 0 or 1.

Today the temperature got up to 101 degrees. The car ran great all day. Occasionally when coasting to a stop right after pushing the clutch in the car would idle really low sub 500. It recovered everytime today, unlike yesterday where the engine died.

I will swap the O2 sensors maybe on Sunday.

The Block Learn Memory (BLM) #s are indicative of the AF mix, long term. 128 is nominal and should be w/in (some say) ± 10 or better (i.e., ±5) in closed loop.

It isn't possible to say THAT is your problem, BUT it very well COULD be. It needs to be addresses - made right - before continuing.

#1 cause of (lean) in CL is the O2 sensors. And, low or zero cross-counts indicate a "lazy" or non-functioning O2 sensor. That will typically be reflected in BLM #s, IF there isn't multiple faults (i.e., something else adding to the overall symptoms!). Let's fix one thing at a time, and see what we have left after that.

Your BLM discrepancy in C/L is what I would expect if one O2's cross counts was low as 1. Cross counts as low as that is indicative of a lazy/dysfunctional O2 sensor; is why trading places with the O2s is one way to see if it the sensor, or perhaps something else. My guess is if the low counts follow that sensor, you can plan on replacing one - if not both sensors. Let's try swapping sides and see what happens to cross-counts, and after a short trip around the block a few times, see what the left/right BLMs are. (Might want to erase the BLMs by first disconnecting the battery for a minute before going for a drive so they can "reset". Then see what changed, if anything.)

Gotta run!

[Billy Mild]

Would unplugging all the plugs to the ECU be enough or do I need to unhook the battery for 10 minutes to completely clear it?

The car has been running just fine the last few days in the extreme. Its like she is back in action now. I'm guessing the larger gap of the old plugs(5000 miles old) and the extreme heat were causing some misfires.

I will reset the ECU later this weekend along with swapping the O2 sensors side to side.

[Paul Workman]

Just unhook the positive cable from the battery for a minute. That will reset amy cades as well, clean slate!

[LGAFF]

have you checked your MAT sensor?

[Billy Mild]

have you checked your MAT sensor?
I have not. After the plug swap it seemed to run better. The car overall today seemed to run pretty good.

I still notice when coasting that it has a slight backfire and burble that I don't think should be there.

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[Billy Mild]

I still have the slight backfire in the exhaust when coasting to a stop and in gear.

I had a few hesitations today when at a lower speed and going 25-50% throttle. It almost cut out. I do now have some datalogs. I'm not sure how to look at what is going on from the logs?

I noticed BLM when at part throttle are NEVER at 128. They are always at 125-112. That seems rich, but would O2 sensors affect this reading?

[BigJohn]

So that's what that is called!

[Billy Mild]

Is there anyway to upload my catalogs?

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[XfireZ51]

I still have the slight backfire in the exhaust when coasting to a stop and in gear.

I had a few hesitations today when at a lower speed and going 25-50% throttle. It almost cut out. I do now have some datalogs. I'm not sure how to look at what is going on from the logs?

I noticed BLM when at part throttle are NEVER at 128. They are always at 125-112. That seems rich, but would O2 sensors affect this reading?

The BLMs are indicating what the O2 sensors are reporting over the long term.
Difficult if not impossible to always get 128s. Depends on the time and gas u want to burn. Acceptable BLMs range 128 +/- 6. The tighter the better. Also, there will definitely be a disparity between left and right banks. Typically left runs leaner than right side particularly at idle. At PT cruise, it tightens up.
On the backfire, has your calibration disabled Decel Fuel Cutoff? Its also a function of the amount of fuel in the runoff or decel area of the VE(fuel) tables.

[Billy Mild]

XFireZ51, I have a Marc Haibeck tune in my car. Anti backfire mode is enabled as well as extra fueling for the headers I have on my car.

Before swapping headers the car ran soo smooth. I'm wondering if this is all due to the new O2 sensors I installed in the car at the time of the header swap. I didn't make near as much power on the dyno that I would expect from a tuned header car and it occasionally stumbles at part throttle. I have changed the plugs and for the most part it doesn't feel like an ignition misfire.

I will try to do some more datalogging, but my battery needs to be replaced. This is the second time it has gone dead over night.

[XfireZ51]

Marc has stated before that the stock tune on an LT5 is a bit on the rich side, so the addition of headers will lean things out a bit to the better. However, an "out of the box" tune is not likely to be optimized for each individual motor and config. Most "tunes" focus on WOT, whereas part throttle, cruise, idle is a whole 'nother matter.
Frankly, I would not suspect the O2s unless you see something in the datalogs showing signal dropout or a lazy/poisoned O2. The ECM has a very limited range of accommodating some changes but its not "autotune". Especially the OBD1 versions.

BTW, make sure the exhaust has no leaks. High vacuum on decel will suck in fresh air and ignite unburned fuel mixture causing a backfire. The presence of fresh air will also signal a lean condition to the ECM by the O2s and so causing the ECM to add fuel. So if DFCO is disabled, ECM keeps adding fuel.

[Billy Mild]

I ordered a tune from Marc for post header install. I installed the chip before I had the headers put on and it ran great.

A few weeks after the headers this crap started up that I really noticed.

[Billy Mild]

Replaced the battery and the car fires right up.

I did some more ALDLDroid datalogging today. I noticed that when I had the hesitation, it was after slowing down to a stop then getting back on the throttle. The LEFT INTEGRATOR signal was down in the low 80's. I have the datalog files if anyone would like to review them. I don't even know how to open them on my PC.

I would like to thank everyone up to this point.

[XfireZ51]

Replaced the battery and the car fires right up.

I did some more ALDLDroid datalogging today. I noticed that when I had the hesitation, it was after slowing down to a stop then getting back on the throttle. The LEFT INTEGRATOR signal was down in the low 80's. I have the datalog files if anyone would like to review them. I don't even know how to open them on my PC.

I would like to thank everyone up to this point.

If you can ship them as a .csv file, I can review it.

[Billy Mild]

https://www.dropbox.com/sh/cln5qzfq0dc9b1d/AABAzz8_nNWKp2Pms4G9dmFxa?dl=0

Here is a dropbox link with the most recent ALDL Datalog. I used the "Mark Datalog" feature, but I'm not sure what that means.

[Billy Mild]

I drove the car this morning and it had a high idle(1200-1500). I shut the car off and restarted it, and it ran smooth as silk and the idle was completely normal 700-800 RPM.

[XfireZ51]

I drove the car this morning and it had a high idle(1200-1500). I shut the car off and restarted it, and it ran smooth as silk and the idle was completely normal 700-800 RPM.

Billy,

U went thru the reset for the IAC.

[Billy Mild]

http://uploads.tapatalk-cdn.com/20161010/b7bd8dcf110f9782ab3e129961bc4a79.jpghttp://uploads.tapatalk-cdn.com/20161010/5259b92fe6d622462706576b663cfb08.jpg

What is this integrator number?

When decelerating to a stop when in gear I notice the BLMs go to 110-120. I assume this is Marc's way of doing anti backfire mode.



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[XfireZ51]

BLM - Block Learn Multiplier - This is the long term fuel trim

INT - Integrator- This is the short term fuel trim.

Over time changes to the INT cause changes to the BLM. Usually these two tend to move in opposite directions so if the BLM is > 128, the INT will try to drag the BLM towards 128 by going the opposite direction.
Disabling DFCO allows fuel to be introduced during decel. DFCO would have cut it off for emissions purposes but then that also creates a situation to where fuel does not get "turned back on" quickly enough and so u get a stall. When n DFCO, the BLMs would lock at 128 since you are basically out f C/L.

[Billy Mild]

I was wondering is somehow fuel on occasion is pooling up in a shut secondary port then when I get back on the throttle it stumbles due to being way too rich.

After testing with a NOS ECM my car seems to run much smoother than with my ECM. I also noticed that BLM numbers are closer to what I would expect.

I need to find a place that tests and fixes these ECMs.

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[XfireZ51]

The ECM only carries out the programming that the prom has on it. It is not its own entity. Datalog it and see if there's any quantifiable difference.

[Billy Mild]

The prom is the same. The only change is the ECM.

I did data log both runs, but I don't know how to analyze the data log from ALDLdroid on my PC. I tried to find an old thread on here about tuning to see how everyone reviews these files.

The reason why I think it might be the ECM is the issue is not consistent. It acts like an electrical issue. When it's really hot out it seems to happen more often.

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[XfireZ51]

The one thing I see in your logs is that Learn becomes disabled sporadically for an unknown reason, but that shouldn't affect much. BLMs overall appear ok, nothing bad really. I used your file on .xls to review.

[Billy Mild]

I can give you the data log from the NOS ECM and see if that looks different.

I have a feeling it will.

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[Billy Mild]

This is a catalog of my car stumbling right at the end. What I noticed is the integrator numbers were really low in the 60's and the exhaust was crackling a bit.

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https://drive.google.com/open?id=0BzKuQ1CCzweXZUZFbmQyZTg3bzA

[Billy Mild]

I did some further testing today. I know the exact scenario that my issue is coming up.

If I run the engine in the 3000+ RPM range and decide to slow down with the car in gear, when it drops below 3000 RPM I start to hear some pops and burble from the exhaust. If I let the car get to the 2000 RPM range then give it a little gas or try to accelerate my car stumbles or hesitates. I got this on the datalog today. It doesn't always do this stumble, but it does more often than not.

This happened using both ECM's. So it might be a sensor OR the tune itself. I did notice that when the INT number is down around 60's when this stumble occurs. If I go WOT it clears right now. Its only for partial throttle.

https://1drv.ms/f/s!AmLeM5vTSQEttmNJ9qMuJUA4Qpyk

Above is my OneDrive link to my folder with both datalog files. If anyone could review them it would be very helpful.

Is it worth looking into my tune as a possible cause?

[LGAFF]

Do you have secondaries removed?

[Billy Mild]

No they are intact and should be working correctly. The car makes good power when at WOT.

My only mods are Haibeck Tune for headers and antiback fire mode turned on, Longtube headers, C6Z06 cats and borla axleback with an X pipe.

[XfireZ51]

On decel, the MAP goes very low, somewhere around 25-30kPa. This is where the fueling is at that point. Although DFCO is disabled and the injectors are still providing fuel, once u crack the throttle the motor takes a huge gulp of air due to the high vacuum. This causes the fueling to go lean (INT LOW) and must be overcome with a pumpshot (AE) particulalrly at small increments of throttle opening i.e. 5-10%. When mods have been made to the motor allowing additional air, fueling should be modified in these areas of the VE table and possibly the AE. Could play w timing also.

[Billy Mild]

On decel, the MAP goes very low, somewhere around 25-30kPa. This is where the fueling is at that point. Although DFCO is disabled and the injectors are still providing fuel, once u crack the throttle the motor takes a huge gulp of air due to the high vacuum. This causes the fueling to go lean (INT LOW) and must be overcome with a pumpshot (AE) particulalrly at small increments of throttle opening i.e. 5-10%. When mods have been made to the motor allowing additional air, fueling should be modified in these areas of the VE table and possibly the AE. Could play w timing also.

Did you take a look at my most recent datalogs?

I have emailed Marc Haibeck about this to get his take. He mentioned that the car was going VERY LEAN and then it tries to compensate by moving the INT numbers to the extreme rich side.

So does this come down to a tuning issue on the PROM?

EVERYONE THANK YOU FOR THE HELP. I'm getting closer to a resolution.

[XfireZ51]

Did you take a look at my most recent datalogs?

I have emailed Marc Haibeck about this to get his take. He mentioned that the car was going VERY LEAN and then it tries to compensate by moving the INT numbers to the extreme rich side.

So does this come down to a tuning issue on the PROM?

EVERYONE THANK YOU FOR THE HELP. I'm getting closer to a resolution.

Didn't look at the most recent logs. Ur description sounds pretty typical. If u tuned carbs, u would recognize the symptoms.
As Marc suggests, the INT is trying to overcome the lean condition but it can't react quick enough. That's why the AE is used. How ever, like all fueling its based on the VE table. IOW, u adjust VE in the Decel area so it doesn't go as
lean as it does, then tweak the AE to compensate for the rest.

[BigJohn]

Do you have secondaries removed?




Happy Birthday!

[Hib Halverson]

1) Dont' assume you have a problem with calibration (the chip) unless the problem you have has always existed. If it has NOT always existed, then it's not a cal problem.

2) I could only see two posts where the actual block learn (LTFT in modern terms) or integrator (STFT) were posted. STFT can be difficult to use for initial diagnosis of a problem but LTFT can be quite revealing. In each of those posts, the block learn has been below 128 which means, as Marc has suggested, the engine controls are reacting to a rich AFR in closed loop by "taking fuel out", i.e.: shortening pulse width to lean the AFR back to stoic.

3) First thing I'd do is swap the O2s side-to-side. If the problem stays then it's something causing that side of the engine to run rich. If the problem moves, replace the O2s.

4) So...what could make one side of the motor run rich? Bad injectors could do it and, based on your earlier discussion of your fuel pressure results and that the FP bled down after ten seconds, I'd suggest you pull all 16 injectors send them to RCEngineering in California and have them cleaned then flow tested. If you have bad injectors and want to replace them with really good injectors, ask RC about the LT5 injectors they sold me and many other Zroners. I had a set of RCs in my 95, Barney. They were installed in 1997 and were in the engine when I sold it in April of 2016. In that 19 years in service, I never had a problem with an RC injector.

[Billy Mild]

1) Dont' assume you have a problem with calibration (the chip) unless the problem you have has always existed. If it has NOT always existed, then it's not a cal problem.

2) I could only see two posts where the actual block learn (LTFT in modern terms) or integrator (STFT) were posted. STFT can be difficult to use for initial diagnosis of a problem but LTFT can be quite revealing. In each of those posts, the block learn has been below 128 which means, as Marc has suggested, the engine controls are reacting to a rich AFR in closed loop by "taking fuel out", i.e.: shortening pulse width to lean the AFR back to stoic.

3) First thing I'd do is swap the O2s side-to-side. If the problem stays then it's something causing that side of the engine to run rich. If the problem moves, replace the O2s.

4) So...what could make one side of the motor run rich? Bad injectors could do it and, based on your earlier discussion of your fuel pressure results and that the FP bled down after ten seconds, I'd suggest you pull all 16 injectors send them to RCEngineering in California and have them cleaned then flow tested. If you have bad injectors and want to replace them with really good injectors, ask RC about the LT5 injectors they sold me and many other Zroners. I had a set of RCs in my 95, Barney. They were installed in 1997 and were in the engine when I sold it in April of 2016. In that 19 years in service, I never had a problem with an RC injector.

1. This stumble after a decel is a new issue. Never had that before. It for some reason feels like its the computer or Tune causing it.

2. I am going to get another datalog to really show the issue.

3. The O2 sensors are new, but are a "Standard" Brand from Rockauto. I have suspected these as well as a possible cause. Normally an engine will just run rich when an O2 sensor is bad.

4. I replaced fuel injectors with Accell brand injectors about 3 years ago. They are the model that Marc recommends on his site. At this time I also did plugs, wires, and fuel filter. I also at that time fixed any vacuum leaks that I could. Just recently I replaced the Spark Plugs again. Do you think I need to send out my 3 year old injectors? According to the FSM if the fuel pump tests show bleed off the pump needs to be replaced.

[Billy Mild]

I will try swapping the O2 sensors around this weekend.

I have been running ethanol free fuel 90% of the time.

[XfireZ51]

Just reviewing the stumble log, what I see is that the secondaries are not opening until 40%+ of TPS opening. MAP kPa is really low at 15 for decel so the motor is operating at the low end of the VE table. Also Spark Advance jumps momentarily from 10d to 25d then drops back to 10 and gradually progresses from there. A bit of Knock Retard as u shut throttle for decel BTW.
Right side running leaner than left for longer period of time, so again I think you r taking a big gulp of air and not compensating for it. O2 sensors appear to be operating nominally. As for replacing them, I have opted for the AC/Delco's rather than the Bosch. Don't know about Denso.

[Billy Mild]

From your oberservations I assume these don't look normal. You are saying that one side of the motor is running very differently than the other side. Right side is leaner than left side.

The spark advance comment I assume means something is out of whack there as well?

I thought the secondaries really only opened IF the motor was over 3000 RPM. Should they also open at a certain TPS setting as well?

As far as my tuning experience I have 0 with FI. I have only tuned 2 stroke motorcycles. Is there a datalog sequence that might be more helpful that what I have gathered thus far.

[XfireZ51]

No I didn't say that. From my observations, it isn't unusual to have one side(typically the driver side) run somewhat leaner than the other. And secondaries come on based on TPS%.
As far as SA, you would need to look at the tables to see if there was some inconsistency or timing anomaly in certain cells, which would not be surprising even for stock calibrations.
As for data logging, I try to do a drive with a variety of elevations and speed trying to come up w about 30k frames. Tuning is an iterative process that zeroes in on a better tune. The objective is to gather data in as many of the cells represented by the VE and SA tables.

[Billy Mild]

Do you try and get some WOT runs and part throttle running when datalogging?

I just feel like I can't be the only person having this issue.

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[XfireZ51]

Do you try and get some WOT runs and part throttle running when datalogging?

I just feel like I can't be the only person having this issue.

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WOT requires use of a WB O2, so no I don't try to do WOT tuning. Besides, the fueling for WOT is dependent on Part Throttle, so PT needs to be correct before moving onto WOT. Also it's safer to do WOT runs on a dyno.

[Billy Mild]

WOT requires use of a WB O2, so no I don't try to do WOT tuning. Besides, the fueling for WOT is dependent on Part Throttle, so PT needs to be correct before moving onto WOT. Also it's safer to do WOT runs on a dyno.
Will this datalogging eventually lead to a cause of my stumble?

You mention my car is taking a big gulp of air. I would assume everyone's car would in the same situation, but maybe my tune doesn't have that portion of the VE table tuned in.

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[XfireZ51]

Will this datalogging eventually lead to a cause of my stumble?

You mention my car is taking a big gulp of air. I would assume everyone's car would in the same situation, but maybe my tune doesn't have that portion of the VE table tuned in.

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When u modify the car and enhance breathing, it requires changes to the fueling. With carbs, u would need a bigger pumpshot and larger jets.

[Billy Mild]

Understandable. That's why I had a tune done for the car by Marc Haibecks. Extra fueling for the headers along with a few other mods like removing CAGS.

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[Billy Mild]

I still have this stumble occasionally. Something I noticed is that the INT's are way off side to side, also the MAP sensor is reading around 91 kPa, as well as TPS around 40% or so.

Could this be a faulty MAP sensor causing my issues? Idle seems to be pretty stable overall, but there seems to be one spot in the tune that seems to be an issue. It is usually after slowing down on decel, then give the car a little more throttle below 50% TPS where the car will almost stumble. I do notice that kPa goes really high at this point. I'm guessing that isn't normal.

Thoughts?

Datalog files:
https://1drv.ms/f/s!AmLeM5vTSQEttzvdv7u4r38fklHt

https://1drv.ms/f/s!AmLeM5vTSQEttzxJLTbggfqsgumq

[Billy Mild]

Tonight I did a little more driving with my old school Snap-On MT2500. I set the lights for Closed Loop, Port Throttles closed, and Knock detection. For the the first time since this started I have a common thread, when the stumble occurs after decel, when the car is around 2000ish RPM and I give the car 30-40% throttle, the knock light goes ON, and the car stumbles, the secondaries appear to open as well. Very interesting IMO. So I believe it is due to a knock being detected, now I don't know if there really is a knock.

Unfortunately I don't have a stock chip anymore. Would it be worth test driving with a stock 91 chip to see if anything is different?

[Hog]

Tonight I did a little more driving with my old school Snap-On MT2500. I set the lights for Closed Loop, Port Throttles closed, and Knock detection. For the the first time since this started I have a common thread, when the stumble occurs after decel, when the car is around 2000ish RPM and I give the car 30-40% throttle, the knock light goes ON, and the car stumbles, the secondaries appear to open as well. Very interesting IMO. So I believe it is due to a knock being detected, now I don't know if there really is a knock.

Unfortunately I don't have a stock chip anymore. Would it be worth test driving with a stock 91 chip to see if anything is different?
Mr Mild, you say you are getting some knock sensor activity when you open the throttles suddenly?
I wonder if you are getting some "Burst Knock"? Burst knock usually occurs during heavy throttle transitions. Some calibrations will pull ignition timing advance in these areas to avoid the real knock.
Could also be some lean knock with all the extra air rushing in with the sudden opening of the t-body throttles and Port throttles opening up quickly. In this case some extra Acceleration Enrichment could help?
Just some brainstorming on my part.

[XfireZ51]

Tonight I did a little more driving with my old school Snap-On MT2500. I set the lights for Closed Loop, Port Throttles closed, and Knock detection. For the the first time since this started I have a common thread, when the stumble occurs after decel, when the car is around 2000ish RPM and I give the car 30-40% throttle, the knock light goes ON, and the car stumbles, the secondaries appear to open as well. Very interesting IMO. So I believe it is due to a knock being detected, now I don't know if there really is a knock.

Unfortunately I don't have a stock chip anymore. Would it be worth test driving with a stock 91 chip to see if anything is different?


Port Throttle at 2000rpm open at ~ 34% TPS for stock cal.

There is a brief interval where secondaries do not come on to give time to the secondary throttle plate to fully open. If you are in decel w DFCO enabled, its going to take a bit to get fuel to the chambers when you get back on the pedal. Need to look at the knock counts to determine severity of the knock and its duration.

[Billy Mild]

Mr Mild, you say you are getting some knock sensor activity when you open the throttles suddenly?
I wonder if you are getting some "Burst Knock"? Burst knock usually occurs during heavy throttle transitions. Some calibrations will pull ignition timing advance in these areas to avoid the real knock.
Could also be some lean knock with all the extra air rushing in with the sudden opening of the t-body throttles and Port throttles opening up quickly. In this case some extra Acceleration Enrichment could help?
Just some brainstorming on my part.

Never heard of burst knock until your post. This is an interesting thought.

Port Throttle at 2000rpm open at ~ 34% TPS for stock cal.

There is a brief interval where secondaries do not come on to give time to the secondary throttle plate to fully open. If you are in decel w DFCO enabled, its going to take a bit to get fuel to the chambers when you get back on the pedal. Need to look at the knock counts to determine severity of the knock and its duration.

DFCO is on with a stock tune correct?

Haibeck enabled his "Anti-Backfire" mode on my chip.

When I get my OBD1 Bluetooth adapter back I will be doing some more datalogging to hopefully get those knock counts you are talking about.

Another thought I had is maybe one of my coils was having issues that clears up once in a while. Is there anyway to test for a bad coil without pulling the plenum?

I have to say thank you in a advance for giving any kind of advice. I finally figured out how to use TunerProRT to review my datalogs which is really freaking cool.

[Billy Mild]

I noticed for a cold start that smoke pours out of the exhaust. It smells like the engine is running really rich when cold. Is this behavior normal?

https://youtu.be/xxOwdnuKfD8

https://youtu.be/Dj1_KrkSAYs

[Billy Mild]

I took old girl out for some driving today. I think I have figured out what causes the stumble. It appears to happen around 2000-2400 RPM. It occurs in decel with no throttle input, as soon as I start to open the throttle again it seems to almost stumble like its struggling to breath. When I open the throttle open further 30% or more the secondaries kick in and it cleans up.

Could it be the transition from closed to open secondaries? I am going to see if they are being requested but not opening.

[mhobtr]

I noticed for a cold start that smoke pours out of the exhaust. It smells like the engine is running really rich when cold. Is this behavior normal?

Mine smokes like that and then clears up but I don't get that black spray on the floor.

That spray looks like water condensation in the exhaust which blows out when you start it.

[jss06c6]

Billy,

Don't know what your outside temps are, but this steam is normal for cold start. It should go away when the engine warms up.

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[Billy Mild]

Tonight I finally got a SES light. Codes 55, and 64 popped up. After I had my scanner on I cleared them and 55 stayed. It appears that this might lead to a fuel pump issue. That would make sense.

How big of a job is replacing the fuel pumps on this car?

Similar issue:
http://zr1.net/forum/showthread.php?t=19619&highlight=fuel+pump+replacement&page=3

Where is the secondary port solenoid switch at?

[Billy Mild]

I replaced the fuel pumps last night and the car overall runs better. Smoother idle, feels like more power up top. The stumble still remains.

Conditions when it happens, decel from 3000+ RPM slow down to around the 2000-2200 RPM range and give it just a little throttle 10-20%. It will stumble. I noticed while on decel the left side INT drops drastically from 120-125 range to 64, while the right side stays around 120-125ish maybe 113. I notice the lower INT on the left side the worse the stumble is. If I got WOT the stumble stops right away, but I think that has to do with it is enriching the mixture immediately and ignores the sensors. This stumble happens with power key ON or OFF

So on the scanner I'm not sure what side of the engine is the left vs. right side. Could this be an exhaust leak, O2 sensor issue, or something else?

[XfireZ51]

You have headers and exhaust. In decel, you have high vacuum and basically with the increased breathing the exhaust provides, it could be necessary to richen up the AE pumpshot at lower TPS% changes.
Again, Billy it would be helpful to see what the % TPS change is at the time of the stumble, plus are the secondaries kicking in or is this happening w just the primaries.

[Hib Halverson]

I replaced the fuel pumps last night and the car overall runs better. Smoother idle, feels like more power up top. The stumble still remains.

Conditions when it happens, decel from 3000+ RPM slow down to around the 2000-2200 RPM range and give it just a little throttle 10-20%. It will stumble. I noticed while on decel the left side INT drops drastically from 120-125 range to 64, while the right side stays around 120-125ish maybe 113. I notice the lower INT on the left side the worse the stumble is. If I got WOT the stumble stops right away, but I think that has to do with it is enriching the mixture immediately and ignores the sensors. This stumble happens with power key ON or OFF

So on the scanner I'm not sure what side of the engine is the left vs. right side. Could this be an exhaust leak, O2 sensor issue, or something else?

Just guessing, here...

If the bank 1 integrator is going down to 64, that means the system is taking a whole lot of fuel out. If the stumble is worse, the lower the bank 1 integrator gets--that makes sense.

I'm going to guess that the stumble is being caused by a suddenly way lean AFR (64 integrator) and that the system, while in closed loop, cannot change states (from a pulse width typical of a 64 integrator to a pulse width wide enough to provide proper fueling) fast enough to prevent a lean sag during a modest throttle opening.

You don't get the stumble when you go straight to WOT because the engine goes instantly to open loop with both integrators at 128.

Let me know what you think.

[Billy Mild]

You have headers and exhaust. In decel, you have high vacuum and basically with the increased breathing the exhaust provides, it could be necessary to richen up the AE pumpshot at lower TPS% changes.
Again, Billy it would be helpful to see what the % TPS change is at the time of the stumble, plus are the secondaries kicking in or is this happening w just the primaries.

I will run a datalog and try to limit it down to when the stumble is occuring a little before and a litttle after.

The thing is the stumble goes away if I just go WOT. I have noticed that sometimes it is not during secondary operation. once the secondaries come on it may stumble at the low 25-30% throttle opening The sound the engine makes is terrible as well. I will try and get a video of that too.

[Billy Mild]

Just guessing, here...

If the bank 1 integrator is going down to 64, that means the system is taking a whole lot of fuel out. If the stumble is worse, the lower the bank 1 integrator gets--that makes sense.

I'm going to guess that the stumble is being caused by a suddenly way lean AFR (64 integrator) and that the system, while in closed loop, cannot change states (from a pulse width typical of a 64 integrator to a pulse width wide enough to provide proper fueling) fast enough to prevent a lean sag during a modest throttle opening.

You don't get the stumble when you go straight to WOT because the engine goes instantly to open loop with both integrators at 128.

Let me know what you think.

This sounds accurate. I don't know what would be causing the lean condition. Could it really be as simple as O2 sensors?

[Billy Mild]

Video to follow. Here is one Datalog that shows the stumble. Anytime the INT hit 64 on the left side the car would pop/backfire through the exhaust and if I go lightly on the throttle it will stumble. If I would give the car more throttle then the secondaries would kick in and smooth out the mixture.

I was able to get the secondaries to stay open while on the highway and i slowed down to 2000 RPM while maintaining partial open throttle. There was absolutely NO STUMBLE when the secondaries were open at 2000 RPM.

Does that sound like a tune issue or something else?

https://youtu.be/Tntnk9KFTQg

https://1drv.ms/u/s!AmLeM5vTSQEtuBsaMsSzfVVO565i

Datalog file to follow the video.

[tpepmeie]

I haven't looked at your data logs. When the int goes low, do the fuel pulse widths go to zero? That would be expected when decel fuel cutoff is active. Given your description it sounds like conditions where dfco would be active. It's easy to disable in the calibration to check if that makes a difference.


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[XfireZ51]

Todd,

I think Billy originally stated that this was a Haibeck calibration w DFCO disabled. If this were my motor, I would try either increasing fuel(3-4%) in the
Port Throttle Closed VE table for the cells in the vicinity of the rpm/kPa where the stumble occurs, and/or increasing the AE pumpshot at the 0-5% of the
AE v TPS% change table. Again, probably starting w 3-4% increase. I'd need to take a look at the bin just to determine how it varies from stock.

[Billy Mild]

I haven't looked at your data logs. When the int goes low, do the fuel pulse widths go to zero? That would be expected when decel fuel cutoff is active. Given your description it sounds like conditions where dfco would be active. It's easy to disable in the calibration to check if that makes a difference.


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Haibeck was supposed to enable the "anti-backfire" mode for my tune. My only issue is that the LEFT side is the one that goes very low on the INT side. The right side INT goes down to only 110 or so.

Todd,

I think Billy originally stated that this was a Haibeck calibration w DFCO disabled. If this were my motor, I would try either increasing fuel(3-4%) in the
Port Throttle Closed VE table for the cells in the vicinity of the rpm/kPa where the stumble occurs, and/or increasing the AE pumpshot at the 0-5% of the
AE v TPS% change table. Again, probably starting w 3-4% increase. I'd need to take a look at the bin just to determine how it varies from stock.

On my old 944 Turbo there was a switch on the ECU to do just this without changing the tune at all. Is that possible on the ZR-1?

[XfireZ51]

Haibeck was supposed to enable the "anti-backfire" mode for my tune. My only issue is that the LEFT side is the one that goes very low on the INT side. The right side INT goes down to only 110 or so.



On my old 944 Turbo there was a switch on the ECU to do just this without changing the tune at all. Is that possible on the ZR-1?

Ah, no such switch. You probably had something like a "bin switcher" on the Porsche to fatten up the fuel. The disparity between left and right banks is not unusual especially in high vacuum situations. It could also indicate a vacuum leak of some sort. On decel, fresh air could be getting sucked past the O2 sensor. Check to make sure there isn't an exhaust leak somewhere on the left side. Perhaps near the collector.
How recent are the O2s?

[tpepmeie]

Good point about the exhaust leak and/or O2 problem Dom. I very much doubt it's calibration related.


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[Billy Mild]

My o2's were replaced when I put the headers on late last year. The o2 sensors were "Standard Motor Products" brand from RockAuto. I did use a O2 extension harness on the passenger side header. I have the o2 extension harness wrapped in wire loom and DEI high temp reflective tape to help prevent it from melting.

So I should be looking at a leak possibly on the passenger side of the exhaust or maybe the O2 on the left side is lose maybe? I will try and jack up the car and see if there are exhaust leaks.

[A26B]

My o2's were replaced when I put the headers on late last year. The o2 sensors were "Standard Motor Products" brand from RockAuto. I did use a O2 extension harness on the passenger side header. I have the o2 extension harness wrapped in wire loom and DEI high temp reflective tape to help prevent it from melting.

So I should be looking at a leak possibly on the passenger side of the exhaust or maybe the O2 on the left side is lose maybe? I will try and jack up the car and see if there are exhaust leaks.

Check the plug connector on the passenger side O2 extension to insure there is no moisture. An O2 signal short will cause problems in closed loop only. In particular, if the elec connector is under the HVAC condensate drain, water can drip on the connector. (actual experience encountered on my ZR-1;))

[XfireZ51]

Since the left (driver's) side appears to be leaner than the passenger, I would check that first. I would also swap the O2's for AC Delco units.
Finally, make sure the O2's or the wires are not covered by anything. The way the O2 works is to compare ambient air to the mixture coming down from the exhaust. So air needs to move freely into the sensor itself.

[Billy Mild]

Since the left (driver's) side appears to be leaner than the passenger, I would check that first. I would also swap the O2's for AC Delco units.
Finally, make sure the O2's or the wires are not covered by anything. The way the O2 works is to compare ambient air to the mixture coming down from the exhaust. So air needs to move freely into the sensor itself.

The O2 sensor and wiring is how it is from the box. The O2 extension harness from SW is covered with wireloom and DEI high temp tape.

[Billy Mild]

I swapped the O2's from side to side. There was no difference in how the car ran. It had the same issue of Left INT going to 64 or so.

The O2 readings seemed about the same as well on ALDLDroid. I looked over the exhaust and there is no black soot at all on the outside or at the flanges for the exhaust. I did notice when I swapped the O2 sensors that the driver side had a lot less soot on it. The passenger side had a lot of soot.

Any other ideas?

[XfireZ51]

It doesn't need to be a large leak. May not see any exhaust trail. Remember what could be happening is fresh air being sucked in and going by the O2 sensor.
What does the O2 voltage look like side by side during the time this is occurring?

[Billy Mild]

I held my hand around the flange at the header and didn't feel any air movement.

It appears that that left side mV 800-900, right side mV . 200-300 while decel. Now right when I start to get back on the throttle it appears my car right side the O2 sensor goes up and down. The left side seems to stay more steady while the stumbling happens. I will do a datalog with the swapped O2 sensors. I assume this will make no difference.

[Billy Mild]

http://zr1.net/forum/showthread.php?t=26006&highlight=DFCO

http://zr1.net/forum/showthread.php?t=23806&highlight=DFCO&page=3

There are a ton of these posts, but no resolution. Same thing, mods, custom calibration from Marc, then stumble after decel.

I'm getting a stock PROM to see if that cleans it up at all or makes it worse.

[jss06c6]

Billy,

Trying to recall if you have deleted the secondaries. If not, and you have not tuned your VE tables, your fueling will be "close" but not where it should be. In addition, you can edit the DFCO sequence to allow more fuel during deceleration which may help with your stumble upon acceleration. However, you'll need to get your fueling right with your VE tables first.. I've had to make some pretty good changes to mine after adding headers and high flow exhaust. Once you change spark, you'll need to go back to the VE tables and adjust again. It's an iterative process. Marc will get you close, but each engine and setup is unique enough to require fine tune to get the engine into it's happy zone..

Remember as well, that Marc typically installed a "piggyback" chip which works in concert with your stock PROM. We can get the stock BIN file and burn a new EPROM to replace the Haibeck chip, but I don't believe this will be the issue (certainly can be wrong here).

Steve

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[jss06c6]

You can also change the point at which your secondaries are commanded open..

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[Billy Mild]

I'm not a tuning expert and honestly have no idea how to change the tune on a FI car.

DFCO should be turned off on my car per my tune. I may try and switch out my O2 sensors again with a different brand to see if that helps. My car looks to try and really richen up the mixture on the left side of the engine. I'm wondering if it is loading up on fuel and thats why it hesitates when tipping in the throttle again.

[XfireZ51]

Bring it to Chicago.

[jss06c6]

Bring it to Chicago.

That certainly would be time well spent!:cheers:

[Billy Mild]

Well this thread is going to flipped upside down.

I just recently purchased a NOS 1991 PROM. I wanted to try out a stock tune on my car and see how it reacted. It is very interesting how the car reacted. No stumble at all under the exact same conditions as before, and I noticed that the BLM/INT's were more consistent side to side. With my Haibeck tune the INT's get way off from side to side, and during a decel drops to a really low number. The stock tune never got below 115 on INT or BLM's. Very interesting. It appears the O2 sensors worked better as well. The car did backfire quite a bit during deceleration.

I will attach the datalog. This points me to a tuning issue for my Decel, tip in, stumble issue.

To look at the datalog you will need to change from .pdf to .xdl file extension. Could someone review and compare?

[XfireZ51]

There are 2 stock chips for every year. Do u happen to know the "broadcast code" for the chip u bought?

[rush91]

Sorry your having such issues.....But DAMN I love the sound of your Beast! I'm running a stock chip and sometimes get a backfire on acceleration but never on decel....

[Billy Mild]

There are 2 stock chips for every year. Do u happen to know the "broadcast code" for the chip u bought?

Would a picture of the chip help?

[-=Jeff=-]

Would a picture of the chip help?

yes, he wants the info off the silver label on the MEMCAL..