Really need help with the last small issue with my 90

[Corvette95]

My car will hesitate and stumble and die ONE TIME on cold start up...rest of the day, even back to back start up is fine...here is my post and I am adding video with Tech1 data. When my 90 sits overnight or longer, on the very first start of the day it will start immediately rev up to over 1000 rpm stumble down to 600 ish and 9 out of 10 times die. Now, I know what it sounds like BUT....did this before injectors were replaced last week. Did a leak test on the old and new injectors while on rail, old injector on #6 and a tiny drip so I replaced primary and secondary injectors. New fuel pumps (part of a restoration), have fuel pressure gauge on rail (Carters Y, new lines and clamps), with key on pressure goes to 49 then down to 42 and holds during start. Used fuel pump jumper wire, both pumps work and even tried starting with jumper wire to both pumps-no change. Fuel pressure hold steady 2 plus hours after key off- no leak. After first start and stumble or die, restart is perfect...idle to 1100-1200, smooth then idles slowly down to 650 ish smooth idle. TPS is .54 . Throttle body rebuilt by Haibeck last month. IAC count could is around 150 before start up cold then slowly moves down from 50 to single digits. Coolant temp sensors are working both ambient air and water temp. No wire arcing, wires were ohmed good. No vac leaks, secondary runs 2 seconds and holds 4-5 minutes before short cycle. No codes ECM/CCM. Runs perfect other than that. Intake accordian has sleeve to prevent collapse. Engine is low mileage, recently top end port (Pete) and refinish. Stock new Delco air filter with open lid. Just added oil catch can to PCV. Marc Haibeck says he has never seen this and likely could not tune it out. Again, this will happen once...no more that day. Hopefully someone can help and maybe some of the Lotus engineers still here since it is a very low production number with steel half shafts. Replaced cam sensor due to plastic broken when I replaced oil seal. Again, no codes. I would say it sounds like an air leak in the intake but none found. Fuel pressure - every test in the FSM is good. New FPR from Jerry's anyway during restoration. A/C on IAC adjusts idle correctly. See addition post for additional new information about fuel bypass mode....

https://vimeo.com/446827957

[Ccmano]

Have you watched the IAC counts when this happens on a Tech1 or such?
H
:cheers:

[Corvette95]

Hans, the IAC when cold and KOEO, is 150, when it starts it goes to 50 then progressively lower to single digits then 0. What I have been researching is on start up the knock sensor retards timing 3 degress as it shows a start up only spark knock after that, I cannot get any knock at any rpm. Now according to the FSM, the car starts on backup fuel below 400 RPM. after start up spark advance is steady at +8 degrees, throttle blip will lower advance for split second then advance it up to teens and lower twenties. Car runs like a top after first start. NOW INTERESTING THING I FOUND is if I select backup fuel when it is running fine hot or cold it runs like crap on backup fuel...that could be something. Fuel pressure at first ignition cycles runs both new pumps to upper 40's then bleeds off to low 40's, start up fuel pressure drop to 39-40 for split second during crank revolutions then back up to low 40's. If I cut the car off pressure holds in 40's for 2 hours. Now the FSM says both pump should re-energize on new key cycle with coolant temp under 100 + degrees - don't remember exact temp both pump quit being energized and only the primary energizes when warm but a new key cycle with coolant temp under 100 will only activate primary, but either way fuel pressure is over 40. Map sensor is giving good info. I reset the fuel block learn and it runs at 118/119 and has a short term learn factor of 5 so it is rich but rich should make start easier? No codes at all. I would appreciate help on this matter as I have researched every avenue I know of. Anyone know if a quick measure of spark knock on start up is normal?

[grahambehan]

I saw your video showing -3 degrees of spark on your initial start up, there is a rudimentary form of cat light off spark if the car is started within certain coolant Temps, emission territory. This table has a max authority off -10 degrees. Does your calibration have this addressed?

Graham

[Paul Workman]

I wish I could add something to the discussion on the 90. Your data on the Tech-1 is very similar to my results: nothing different enough to mention, even.:neutral:

However, my wife's 91 acts exactly the same way on first startup of the day, UNLESS I blip the throttle as it stumbles down to idle. (Oh, and the 91 also has a elevated idle when it fires, but more like 1400 to 1500 rpm (instead of 1900 ish rpm for 4-5 second for the 90) before settling after 2-3 seconds.)

Other than that, it runs like a top. So, now I anticipate the stall on first start of the day, and a quick blip of the throttle is all it takes to avoid it. After that and on subsequent starts during the remainder of the day, she fires up almost instantly - with gusto (Pete's cams in her car).

I get no codes, and because that blip is all it takes to cross over the stall, I just shrug and never give it another thought.

Your mileage may vary!:cheers:

P.

[Corvette95]

So this morning, pulled the wire from the knock sensor before starting so no retard on startup...no difference. First crank engine fired up to 1000+ rpm stumble then dies..all with 40 psi for fuel pressure. Verified MAP sensor was giving correct readings before start up. Second start up fine. Now, on cold start up Tech 1 shows desired engine speed 3187 until first engine revolution then changes to 875 or so. I don't know if that is something or not.. It will repeat the same desired RPM on restart as well and it starts and runs fine. OK, new detail this morning. If I set to backup fuel on tech 1 the fuel pressure bounces from 40-50 (see video https://vimeo.com/447820587 ) . It will also pop/small backfire on heavy throttle blip on backup fuel only) . Any ideas?? Graham.... low mileage 90 with stock calibration. Recently bought and have restored..only mods were top end porting by Pete, open air lid, and cat back exhaust. When on closed loop it shows a BLM of 118 with short term trim of 128 both banks.

[Corvette95]

I wouldn't think plug wires or coils since it runs so well after the first time and no codes. I did not replace the coils,as they were not original. I did replace the #8 wire only..other ohmed good.

[Corvette95]

126471264812649


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[Ccmano]

What I'm interested in is what the IAC is doing when it stalls. Is it showing a reading or is it at zero? I prefer to analyze things from the perspective of "Accams Razor", looking at the simple things which are more likely before we get carried away with a multitude of complexity.
H
:cheers:

[grahambehan]

Prev post said 150 iac, park position prior to start, 50 counts at start, dropping to single digits/0 counts.

[Ccmano]

Prev post said 150 iac, park position prior to start, 50 counts at start, dropping to single digits/0 counts.

Thanks Graham, missed that. That tells me the IAC is not controlling the idle speed (zero count) at the point it's stalling. We have found before that the base mechanical idle adjustment of the throttle body sometimes has to be redone when the intake has been ported. To me the next step would be to readjust that. I have to do a search but it's out there in the tech forum.
H
:cheers:

[Corvette95]

Hi, to clarify, the IAC is at 150 on start then comes down. When the first start happens and it dies, the IAC count is still around 80-100. I just finished replacing both fuel pumps again...they were new Airtex, I went with Delco pumps this time, no significant change, I have maybe three more psi at all ranges with the new pumps...no change in leakdown. What I wonder about is the requested RPM before start that shows 3000K plus requested but first revolution in crank sequence brings requested RPM immediately down to 875. Car runs rough in back up fuel and I wonder if the back up fuel controls the initial start up air and spark until the ECM sees 400+ RPM? I have asked Haibeck about this and he says he has never encountered this issue before . He initially wondered about the spark retard on start up, but pulled the knock sensor clip off so that wasnt the issue/. He also asked if I had another ECM to swap..I don't, he also asked if my Tech1 was giving accurate readings..well pulled out the old Tech1 with a different Mass Storage Cartridge and I got the same readings ( I found an old Vetronix rep that was selling out and I bought all his extra Tech1 stuff).

[grahambehan]

Ok so the iac is at 80 - 100 at the stall? So as stated adjust the throttle blades further open, I normally shoot for 20- 30 iac counts on a hot idle, some may disagree but thats that. With kr on start up, common lt5 is mechanically noisey, that normally goes away fast. Since you said it is the first start only the car light off reduction is probably active, between 20 and 32 c coolant temp from memory, so it is certainly reducing engine efficiency, a simple change to that will help out with no more sustained negative spark. Outside of those temp ranges there is no spark reduction from the light of feature. After having the engine ported, why no tune, just as a matter of interest.

Graham

[XfireZ51]

Graham,

I believe you meant he should CLOSE throttle blades so more bypass is needed to run motor. At 0 IAC counts, the IAC is fully closed.
By closing blades the ECM would have better control over idle speed. I shoot for 12- 20 steps, again on a hot idle.

[grahambehan]

Well 1 says it goes to zero and one says it is at 80 so both maybe true. Thats why I said a warm idle iac value

Graham

[XfireZ51]

Usually, for me, if the IAC at operating idle is at 0, either the blades are open too wide or there?s a vacuum leak. With a ported top end and rebuilt TB, I suspect Chris? motor is moving more air thru the TB, so closing the blades would bring up the IAC counts.

[Corvette95]

Thank you SO much for the feedback. I will data record from the IAC tomorrow and post results. I will record the live IAC data from cold start in the morning and post! Thanks again .

[Corvette95]

FYI IAC drops from 150 to under 100 after first start then close to near zero after successful start after first. I think this a pre program open loop issue. Can this be tuned out. Will update Saturday morning. Thanks to all!

[XfireZ51]

I think you should do the Min Air adjustment before doing anything else IMO.

[Corvette95]

Ok so the iac is at 80 - 100 at the stall? So as stated adjust the throttle blades further open, I normally shoot for 20- 30 iac counts on a hot idle, some may disagree but thats that. With kr on start up, common lt5 is mechanically noisey, that normally goes away fast. Since you said it is the first start only the car light off reduction is probably active, between 20 and 32 c coolant temp from memory, so it is certainly reducing engine efficiency, a simple change to that will help out with no more sustained negative spark. Outside of those temp ranges there is no spark reduction from the light of feature. After having the engine ported, why no tune, just as a matter of interest.

Graham
So to clarify,adjust the throttle blades to open further? Would that be by adjusting the throttle body idle adjustment screw? Currently TPS is at .54 or are we talking about doing an IAC relearn (or both)? Coolant temp has been steady on start up as I have it inside a climate controlled garage so engine temp is +/- 68F and MAT is +/- the same 68F reading in the morning. Also map is reading correct barometric outside pressure. Also, when warmed up for a few minutes I have a zero IAC count. warm idle is dead on 650 to 675 via Tech1. Also, a new calibration is definitely getting done, this was the last gremlin to tackle before getting a calibration. I will have to order a standard chip for the light mods on my car until I can get it to a ZR-1 specialist. I am in Alabama, last work was done on my 95 10+ years ago by South Georgia Corvette with is an 8 hours drive with a car hauler behind me. I am mostly concerned about the die in case there may be a mechanical issue that I don't want to mask such as a coil, plug, or intake leak. I have done my best to rule it out but I do have a home made "smoke" machine I can test for intake leaks but again, secondary pump runs a few seconds and holds for 4-5 minutes before a very short cycle. I don't seem to notice a difference on start up with normal or full power.

[Corvette95]

So this morning...same temps and humidity as yesterday, I wanted to get another video of the cold start before changing idle air and or IAC reset. NOW THE ONLY DIFFERENCE IN TODAY VS YESTERDAY IS THE TWO NEW FUEL PUMPS that I replaced out of frustration, the Airtex pumps had less than 10 miles and 30 minutes of idle on them (they were new). I replaced with over the counter Autozone pumps with a 53 GPM flow. The first ignition cycle of the day gives a 2 or 3 lbs higher readings than the Airtex. Todays video is of the first morning cold start and IAC readings at start up. TODAY IT STARTED FINE, do note the fuel pressure gauge drops into the upper 30's with ignition immediately turned off then rebuilds to 42+ after about 5 seconds? Cut off and restart was fine...long 2-3 seconds crank time which is normal and once fired, ran fine on all subsequent starts. I am NOT going to do anything else today to see if I can repeat a good cold start tomorrow. Fuel pressure with Airtex pumps was within tolerance but on the low side and held pressure. I don't know but maybe was a bad pump- knock on wood. The IAC counts on start up and other of todays cold start parameters can be seen here. Sorry for the shaky video. https://vimeo.com/448080466 Fuel pressure has held steady for 30 minutes now with engine off at 44 psi. Thanks!

[XfireZ51]

One other thought. With the top end taking in more air, the cranking PW may not be enough initially. However, once it starts and then dies, there still may be enough residual fuel so that it, along w second crank, is sufficient to keep motor running for startup

[Corvette95]

One other thought. With the top end taking in more air, the cranking PW may not be enough initially. However, once it starts and then dies, there still may be enough residual fuel so that it, along w second crank, is sufficient to keep motor running for startup


I get your point and understand but I wonder if this could be help with a custom tune? I did for the sake of doing it tried cranking in flood mode (full pedal) turned ever but never did start up in ten seconds of cranking in flood mode. It was just a shot in the dark. Aren't you running the MegaSquirt? I look at the parameters need to run that...way over my head.

[XfireZ51]

Not running MS. Using stock ECM. I would suspect flood mode wouldn?t work because I?m suggesting the Crank PW is lean. With second crank attempt, there may be enough fuel in chamber to start motor allowing it to transition from crank mode to startup enrichment. Many times, w short duration shutdown, mine will start at key START almost immediately, and I believe it is due to fuel in the cylinder ready to light up. Anyway, that?s what led me to suggest this other hypothesis.
So yes that is something that could be addressed in tune.

[Corvette95]

Alright....almost 24 hours of sitting. Went and tried to start this morning after a single good start yesterday with new pumps..... nope... cranked,started, chugged and died. I have video of initial fuel pressure, initial Tech1 readings and a IAC reading continuous at the first start - again, sorry for shaky video, only had one chance of getting all the cold condition in one filming...so new pumps were not the answer... https://vimeo.com/448270325 IAC started at 150 went to 118 at aprox 1100 rpms then the stumble it went back to 150. So is the consensus here to adjust the idle air screw on the throttle body to give it a higher idle (turn clockwise) and do an IAC reset and relearn? I am ready to buy a chip, was going to do that anyway. I did order a DataCat so I can record all the parameters on one screen. Suggestions???? Thoughts??? I welcome all and any chip advice.

[Ccmano]

I would do the Minimum Air Adjustment (Throttle idle air screw) there is a good discussion of that in the thread referenced below. Although I use method in the Emissions and Fuel System manual (picture) I would also install a bolt, as outlined in the thread, to make adjustments easier.
https://www.zr1.net/forum/showthread.php?t=27764&highlight=IAC

https://farm66.staticflickr.com/65535/50233165902_08de152b3b_c.jpg (https://flic.kr/p/2jwW78h)

For datalogging I use either TunerProRt on a laptop or ALDLDroid on an Android tablet. For a chip (tune) Haibeck, Dominic Sorresso or Pete the Greek (can never remember his last name) all in the Chicago area are the go to folks. In Texas, Crossed Flags Performance, Steve Schroeder is also very good. I recommend a custom tune given your issues.
H
:cheers:

[XfireZ51]

Dynomite has my Min Air adjusting procedure documented
here.

http://www.zr1.net/forum/showpost.php?p=261063&postcount=2

As Hans has pointed out, u?ll want to replace the allen set screw on the TB w a hex head one. GM never intended for the Min Air to be adjusted. At least not the way I have it laid out which comes from my experience doing same and balancing
Xfire TBs.

[Corvette95]

Yes, thanks. I just adjusted my minimum throttle setting approx 1/2 to 3/4 turn. Changed my TPS reading from .54 t 0 .52 . I also did the IAC reset per the exact instructions as above. Requested idle is 675 and the idle is 675-690 with an IAC count of zero. With A/C on rpm request is 710 and the iac is at 18 to 19 counts. I also did a nitrogen smoke test before any of that...zero leaks...smoke only came out the open air lid through the filter. I hooked the smoke to the brake booster vacuum as my source line.

[Corvette95]

So a well known tuner we all know and love, seems to think I need to try a different ECM. Anyone know a source of a ECM or the possibility of loaning me one? Would pay a deposit.

[Corvette95]

For those of you that are following.... this morning..same first start stumble , so today I did the IAC and minimum air adjustment posted by XfireZ71. I moved up the minimum idle as directed with motor restart in closed loop and IAC unplugged to 750 from 675 (XfireZ71) recommended a higher idle but I am starting with this) . Then readjusted the TP sensor that had moved from .54 to .48 due to the min idle adjustment. Locked down the idle. Restarted and revved up to 2000 RPM and cut off. Now I won't know if this helps until a cold start tomorrow. I have about 75 rpm higher base idle with an IAC count of 1 was zero at warm idle. I will post update and may try bumping up idle more tomorrow if no change in starting.

[XfireZ51]

If that was ur first start after unplugging IAC, the 2000rpm zoom was the reset.

[Corvette95]

XfireZ51... I paraphrased on my response as to the procedure but I printed out and followed your steps exactly as written other than not setting the idle quite so high. I did the 2000 RPM set after I reconnected the battery and adjusted TPS to .54 (.56 gave me a 1% thottle angle reading). Shut the motor down and it idles about 75 rpm higher than before but the main thing is I have a 1 IAC count at idle where is was zero count before warm in closed loop. Thanks for the tips, I don't know if that will fix it but I appreciate the help. Expect and update from me tomorrow. I also may have found a dealer with three ECM's in stock, I have them looking for them right now, if they do, I am going to snag one of them! ( I also had previously changed the idle adjustment screw to an 8mm, so I had that going already! )

[Subfixer]

I also may have found a dealer with three ECM's in stock, I have them looking for them right now, if they do, I am going to snag one of them!

If they have 3, get all of them. I'll be in for one if you get them.

[Corvette95]

FYI, I have had ten people PM me about the ECM's so IF they end up even having any, they seem to all be spoken for. Sure looks like an aftermarket opportunity for some company!

[Corvette95]

So no word on ECM's yet. Today was the first day after the minimum idle adjustment and IAC reset for a cold start. Did the same thing, started, fired up, stumbled .... but I tried to see if I could "catch it" with throttle before it died and I was just able to. The following is the IAC counts at cold start up and stumble and with me giving it throttle to prevent stall.... now what? Thanks! https://vimeo.com/448956933

[Ccmano]

After looking at your video, your car is taking too much cranking time before it starts. These cars do have a long crank time, especially when cold, but not that long. Based on the video it took 7-8 seconds of cranking. Thats about twice as long as what I would consider normal.

Please try something for me. Tomorrow morning, get in the car and turn the ignition but don't start the car. Wait until you hear the Fuel pumps stop running. Once the pumps stop turn the key the final amount to crank the car. I want to see if it still takes as long and if it has an impact the stumbling. If nothing else this should eliminate fuel as an issue.
H
:cheers:

[Corvette95]

After looking at your video, your car is taking too much cranking time before it starts. These cars do have a long crank time, especially when cold, but not that long. Based on the video it took 7-8 seconds of cranking. Thats about twice as long as what I would consider normal.

Please try something for me. Tomorrow morning, get in the car and turn the ignition but don't start the car. Wait until you hear the Fuel pumps stop running. Once the pumps stop turn the key the final amount to crank the car. I want to see if it still takes as long and if it has an impact the stumbling. If nothing else this should eliminate fuel as an issue.
H
:cheers:

Hey! I will try anything (what so you want video of while cranking..fuel pressure gauge readings, IAC , readings or anything else?). Todays crank/start took much longer than previous days. It may be related to the minimum air adjustment and IAC reset of yesterday. I will try your test but I am getting both pumps initially on to 51+ psi then drop to mid 40 and holding there during crank...I was going to video it again but tried to keep the clip short. I just replaced the two new Airtex pumps Monday with two new Delphi Pumps. I can energize the second fuel pump with both the Tech1 and the test lead off the harness near the battery so I know both pumps are working (and psi goes back to 50+ - even tried cranking with Fuel pump lead energized-no difference). New FPR from Phil. I am open to any and all suggestions (Marc H has been helping me on the side as well). I will post the start sequence tomorrow. In the back of my mind, when I caught it from dying this morning with throttle , it backfired a little...again, no intake or PCV leaks . And when it starts it runs fine. I dont see how but could this be a coil or spark plug wire issue because it RUNS SO WELL after it starts the second time. Full power mode fine, no codes. Did you notice a 173 IAC reading??? I didn't think it would read over 150??? I am going to reset the min idle back to prior position and do another IAC relearn. Should have done that today but didn;t have time. I also am going to pull the plugs and examine them, it has a constant rich reading on the BLM but that would only help a cold start? Idle after closed loop was 725-750 with a 0 to 1 IAC count. The only thing I have not reversed is the oil catch can addition. I was told the PCV system would not affect the starting regardless. I have the oil catch can plumbed from the left vent tube at read of engine to a catch can below or beside the brake booster and the line in to the PCV dual adapter. It looks really good (IE hidden) as long as it is not a problem. Tank was clean when I got it but I completely drained the tank cleaned every spec of debris out of it before I put the Airtex pumps in with fresh 91 octane non ethanol gas. I found a NOS correct from factory IAC valve I ordered yesterday, I am going to try that too when it arrives this weekend. I also did an injector (primary) balance test, all injectors are working plus I did a rail check for drips and spray..all test good. I am twice over budget on this car, really three times over so I did use Bosch injectors. (all 16) and new orings.

[Corvette95]

I called about the ECM, they said it still had a ticket on it, I would hear shortly. ANYWAY, I got my TunerCat Datacat software and cable in. This is something I have NEVER done. I have always used Tech1 and Tech2 (and now Autel and G-Scan3). What do I need to set to record the data you need to see with my 90's start up issues? I assume just set it to record when I start it, then I assume I find the recorded file and post the file here on the Registry? Anyone know what the file extension is? Thanks

[Corvette95]

While not being able to sleep at 1:14 am. I am likely going to pull the plenum soon and do a visual...I am going to replace the coils and re ohm the wires. I was also reading back through OLD tech articles and I saw this post
"Pull the water seal on the DIS plug back, I guarantee you one of the pins is pushing out when you install the plug, with the water seal pulled back you will be able to tell which pin it is within seconds. I don't remember if these pins are 100 series or not, They are easy to change if needed.
Don't cut or shorten the wire, Take your time and open the crimp connection. Sorry to tell you but the tool is special and a good GM terminal tool is going to cost you about $100.00." Now I know to look for bent pins on the DIS module, thats a given, but not quite sure about this post, does it refer to the DIS harness connector- is there a known issue with the plug itself? Not sure what is meant by one of the pins pulling out. I would want to check this as well, I assume it is a standard metric weatherpack terminal?
__________________

[Ccmano]

While not being able to sleep at 1:14 am. I am likely going to pull the plenum soon and do a visual...I am going to replace the coils and re ohm the wires. I was also reading back through OLD tech articles and I saw this post
"Pull the water seal on the DIS plug back, I guarantee you one of the pins is pushing out when you install the plug, with the water seal pulled back you will be able to tell which pin it is within seconds. I don't remember if these pins are 100 series or not, They are easy to change if needed.
Don't cut or shorten the wire, Take your time and open the crimp connection. Sorry to tell you but the tool is special and a good GM terminal tool is going to cost you about $100.00." Now I know to look for bent pins on the DIS module, thats a given, but not quite sure about this post, does it refer to the DIS harness connector- is there a known issue with the plug itself? Not sure what is meant by one of the pins pulling out. I would want to check this as well, I assume it is a standard metric weatherpack terminal?
__________________

I've had this happen to me. It usually throws a code, depending on which pin is misaligned. If you pull the rear DIS connector and look in on the pins of the DIS you will see a bent pin if that is the case. Sometimes a pin will go next to the connector instead of through it causing an intermittent condition. In this case you'll see the pin only slightly bent to one side or the other. The metal connectors tend to float a bit within the plastic causing this. Highly unlikely this is what is causing your issue.
H
:cheers:

[Corvette95]

OK, so this morning...I do have video of fuel pressure but that is not the issue. Today I started it while recording with DataCat. While Tech1A shows no codes, no RPM drop etc. All HELL breaks loose on first start...I am not sure I can post the video file from the DataCat, but I can post screen shots. First one is from the first start of the day..looks at all the data drops and errors, even no rpms...then look at longer view with multiple restarts, after first start, no errors, no crazy readings. I am not sure to look at crank sensor, cam sensor, DIS or ECM...gotta think about this???

[Ccmano]

OK, so this morning...I do have video of fuel pressure but that is not the issue. Today I started it while recording with DataCat. While Tech1A shows no codes, no RPM drop etc. All HELL breaks loose on first start...I am not sure I can post the video file from the DataCat, but I can post screen shots. First one is from the first start of the day..looks at all the data drops and errors, even no rpms...then look at longer view with multiple restarts, after first start, no errors, no crazy readings. I am not sure to look at crank sensor, cam sensor, DIS or ECM...gotta think about this???

Not sure what I'm looking at? What signals are those? The problem here is you have no basis of comparison. For all we know this could be normal.
H
:cheers:

[Corvette95]

If you look at first photo, that is a screen shot of the first minute of running. The parameters and colors are in the boxes up top that correspond to the graphing lines...It shows RPM count goes to zero multiple times, DIS signal failure several times, Cam sensor signal lost (Green line) (all momentarily) . This is all happening while its running, even though it is idling, the crank reference signal drops to zero (RPM's are the blue line). Basically every major sensor is spiking way up and way down, DIS reference volts there, then gone. This has to be ECM, DIS . I just checked (the best I could) the DIS connection for tightness.... Then the next screen is the restart..all normal, no errors, no spikes in ANYTHING.

[Corvette95]

Here are some more simplified examples...these shows all sensor inputs waaay on and off and out of range .this is again the first start of the day....The lines correspond to the checked boxes above. RPM is Blue.

[Corvette95]

This is second start after cutting ignition off and immediately restarting..every fine and normal.

[Ccmano]

All true, but until I can see similar data from another car that is operating normally we don't know if this is abnormal. Did you start the car as I previously requested, if so what was the result? The other thing that strikes me is the battery voltage. It is suspiciously on the low side of normal at 12.2 to 12.3. I would prefer to see a resting voltage of 12.5 to 12.7. I know it doesn't seem like much but I've seen these cars do very strange things with low battery voltage. When the car is running it should be 13+volts.
H
:cheers:

[Corvette95]

All true, but until I can see similar data from another car that is operating normally we don't know if this is abnormal. Did you start the car as I previously requested, if so what was the result? The other thing that strikes me is the battery voltage. It is suspiciously on the low side of normal at 12.2 to 12.3. I would prefer to see a resting voltage of 12.5 to 12.7. I know it doesn't seem like much but I've seen these cars do very strange things with low battery voltage. When the car is running it should be 13+volts.
H
:cheers:
Yes, here is the video you requested from this morning. It did not stall today... but this is when the datacat was running that you see on the prior posts. https://vimeo.com/449330176

[Ccmano]

Yes, here is the video you requested from this morning. It did not stall today... but this is when the datacat was running that you see on the prior posts. https://vimeo.com/449330176

So it started without the stumble and die out when you let the pumps run. It still cranks a very long time before starting. The long cranking may be related to your readings. What is the battery voltage without the ignition on and once it's running?
H
:cheers:

[Corvette95]

So it started without the stumble and die out when you let the pumps run. It still cranks a very long time before starting. The long cranking may be related to your readings. What is the battery voltage without the ignition on and once it's running?
H
:cheers:
Well, I honestly have done that exact same thing for the past few weeks, even have it past videos posted here. Today was a fluke that it didn't die but I have been watching fuel pressure each time.....I tightened the DIS plug about 1 1/2 revolutions on the 1/4 inch bolt. The voltage ignition off engine off is 12.85 and 14.3 running. Measured with volt meter. I have been keeping a battery tender n it every night. I have a new AC Delco battery here that I am going to swap out and slow charge tonight (just to be sure even though it is brand new) and see how cold start goes in the morning. You are right about possibly voltage related, if not battery itself maybe noise from alternator. Will post again at my regular time tomorrow. Thanks!

[Corvette95]

As I wait for tomorrows cold start, I am leaning (and hoping) this is a bad alternator regulator (was just rebuilt - zero miles on it) or bad new AC Delco battery..it tested good at parts store but still suspect. Here is the first moments of the cold start cycle....

[Corvette95]

So this morning, new battery installed yesterday and trickled charged all night. Starting voltage was 13.35...started..cranked....same thing..DataCat shows all type of issues...restart fine, datacat fine...start....fine. This is what I tried this morning..because if its a ECM issue, why overnight sit? I unplugged battery, sit, rehooked battery, started fine Removed ECM, reinstalled , no change.started fine...WTH? The only thing else I know to do is let it sit again, and start tomorrow with alternator unplugged. I did check alternator voltage while running, no fluctuations..charging +/- 14.10 volts steady?

[Ccmano]

Does the car have headers as well as porting? Are there any other mods?
H
:cheers:

[Corvette95]

No headers. Catback only. I don't understand how it makes a difference to sit overnight and always do the same thing on first start, while unplugged the battery and ECM wont re-create the same issue? What happens on first cold start that doesn't happen after disconnecting battery and ecm and even letting it sit for a few hours? I know there is a lot of brain power here on the Registry. I have the ECM in the freezer right now..trying to figure out how to duplicate more than once a day.

[Ccmano]

Since you have owned it has it ever not had this problem?
H
:cheers:

[Corvette95]

I bought it in February, drove it 5 miles home then the virus hit so I went straight into the restore while the shutdown was going on and I had some help. The only known problem was an intermittent no crank. It just needed the starter relay added which I did, and the starter valley had never been cleaned and I replaced the starter...it fixed the no crank . So I never really drove it, the few times I cranked it before I took it apart I am sure it cranked and died and restarted fine..didn't think anything about it as I figured the full service, fixing vacuum leaks , and other would solve any hard start issues. It received a full by the numbers tune up , restoration, fluids, all. So when it became hard to start back assembled, I knew it wasn't right.there was no reason for it so I began the hunt. It had an aftermarket alarm and vats bypass on it that I removed. Everything is back to stock minus the starter relay.

[Corvette95]

Started fine this morning. Only difference was I unplugged the alternator before first start. Battery was full 13.35 volts. May or may not had anything to do with it. Of course, running like it just rolled off showroom floor right now. I am not going to start it again today and give it a 24 hour cool down.

[Ccmano]

Started fine this morning. Only difference was I unplugged the alternator before first start. Battery was full 13.35 volts. May or may not had anything to do with it. Of course, running like it just rolled off showroom floor right now. I am not going to start it again today and give it a 24 hour cool down.

Was the cranking time any shorter? Mine starts within 2-3 seconds when cold right now.
H
:cheers:

[Corvette95]

Yes, it was 2-3 second crank with no issues.

[Corvette95]

I did having it running later last night than usual , about 6pm so the cool
Down period was a few hours shorter than the others .

[Ccmano]

That would be interesting if 'noise' from the Alternator was interfering with the crank and cam signals to the ECM at cold start.
H
:cheers:

[Corvette95]

too early to tell, but the alternator was rebuilt while plenum was off. Man, I hope that would be the answer to this saga! Tune in tomorrow!

[Corvette95]

Second consecutive day of cold start with alternator unplugged...cranked fine on first start again. Going to let it sit for 24 hours and try tomorrow with alternator plugged back up.

[Ccmano]

Second consecutive day of cold start with alternator unplugged...cranked fine on first start again. Going to let it sit for 24 hours and try tomorrow with alternator plugged back up.

You may be on to something.... 🤞
H
:cheers:

[Corvette95]

20 hours cold sit. Plugged alternator in before first start...turned ignition 3 second crank then start without issue. The saga continues....

[JG95ZR1]

Ever find the issue with your car?


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[Corvette95]

Ever find the issue with your car?


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)


Yep. Alternator pigtail. Car runs perfect. Can balance a nickle on the plenum at 2000 rpms.

http://www.zr1.net/forum/showthread.php?t=32682

[Erik]

Yep. Alternator pigtail. Car runs perfect. Can balance a nickle on the plenum at 2000 rpms.

http://www.zr1.net/forum/showthread.php?t=32682

Whaaaaatttt? What the heck was it doing?