Continued issue when car hits 125 degrees

[LGAFF]

Still having this issue with the car, within about 3-4 minutes of startup, when the car hits 125 degrees, without fail....the car sputters, and misfires, the alt readings drop and flutters. Once the car hits 3K RPM the engine corrects and the problem never comes back until the next time the temp drops below 125.
*Replaced 02 Sensor
*Checked 02 grounds
*Replaced primary fuel pump relay
*tried a different chip
*tried a different ECM
*Changed the plugs
*Checked fuel pressure with car off primary and 2ndry(it still hauls *** so unlikely a fuel issue)

[mike100]

Do you think the coolant temp sensor is reporting accurately? check the plug for it too.

[LGAFF]

Yep its working, the coolant temp moves up and down as appropriate....there must be something that occurs at 125 degrees that is causing the issue....

For example the fuel pumps go back and forth at 167 degrees....I believe the 2ndry starts the car and transitions to the primary

Not sure whats going on....

[XfireZ51]

Still having this issue with the car, within about 3-4 minutes of startup, when the car hits 125 degrees, without fail....the car sputters, and misfires, the alt readings drop and flutters. Once the car hits 3K RPM the engine corrects and the problem never comes back until the next time the temp drops below 125.
*Replaced 02 Sensor
*Checked 02 grounds
*Replaced primary fuel pump relay
*tried a different chip
*tried a different ECM
*Changed the plugs
*Checked fuel pressure with car off primary and 2ndry(it still hauls *** so unlikely a fuel issue)

125F is 51C which is when the motor goes closed loop. Very likely going lean.

[LGAFF]

Dom,

Is there something tied to the O2 sesnors in the ECM that could be bad, I tested the ground(middle white wire) and it was good

[LGAFF]

Going lean because of the 02?

A fuel injector is not going to get better, neither is a pump....unless its a relay...primary replaced...I would think if the engine transitions from the secondary to primary the issue would be the primary relay or pump

if it were the pump....it would not go away

the issue lasts 30 seconds then gone

[XfireZ51]

Going lean because of the 02?

A fuel injector is not going to get better, neither is a pump....unless its a relay...primary replaced...I would think if the engine transitions from the secondary to primary the issue would be the primary relay or pump

if it were the pump....it would not go away

the issue lasts 30 seconds then gone

Yeah I know. It's none of those.

[LGAFF]

I am going to replace the extension harness....are these heated 02s on the 90?

[LGAFF]

I tested the 02s with the tech I, they tested ok....and they give a reading

I thought I had a bad P/S o2.....it was the first to show lean on the tech 1

Its hard to analyze an issue that lasts 30 seconds....

[Franke]

The O2's are heated according to the FSM. Should be 3 wires.

[LGAFF]

yep, three wires...weird stuff..

[Franke]

Since it looks to be a possible temp problem, there is a chart in the FSM the defines resistance values for the CTS and MAT at different temps. Do you get any codes? Have you thought about replacing the CTS? I know its a PITA.

[XfireZ51]

Its not the O2s or anything like that. You have cams similar to the ones I have and I experience the same stumble right at about 47-50C CTS. It goes C/L there and really doesn't like it until the ECM can adjust. Its also still not "learning" at that point. So basically the idea is to delay C/L a bit further up the temp scale. I have played around w a few parameters and at this point the "stumble" is momentary. It recovers quickly. Have you relocated the MAT towards the airbox?

[scottfab]

Going lean because of the 02?

Maybe so. I had one that until I began recording data with a datalogger (diacom) I had no clue. It was "lazy". In your case it could be that the heating element is not getting up to temp before close loop is entered. Then eventually get there with exhaust temps.

A fuel injector is not going to get better, neither is a pump....unless its a relay...primary replaced...I would think if the engine transitions from the secondary to primary the issue would be the primary relay or pump

Pumps can and do fail intermittently. Since your symptoms are so repeatable probably not but....

[QUOTE=LGAFF;181550]if it were the pump....it would not go away

It can in fact go away but not as a function of engine temp.

the issue lasts 30 seconds then gone

Job for a datalogger and then time to study what happening as the close loop bit is set (close loop entered), focusing on which side maybe going lean. Does this symptom happen in full eng power and not? But anyway.... time for a data capture for the full warm up period.

[LGAFF]

So Dom, are you thinking its possibly not a "Physical" parts failure....but that the engine enters a state of ......wait for it......

"Camfusion"

I need to trademark that word

[XfireZ51]

So Dom, are you thinking its possibly not a "Physical" parts failure....but that the engine enters a state of ......wait for it......

"Camfusion"

I need to trademark that word

I think Steven Colbert has already copywrited that term.
The ECM goes C/L at that point. I can see it happening w just my WB. Don't need a scan tool. So the stumble is a consequence of the engine control transitioning from O/L to C/L. There are delays built into the calibration which accommodate the stock setup. Change the cams and things move faster becoming somewhat less stable. So the calibration needs to be modified in order to control the motor more tightly in order to control the instability. In doing the tuning I change parameters in order to keep a tighter leash on the motor reaction to inputs. The stock values tend to exaggerate the inputs to a modded motor.
As I have explained at other times, part throttle tuning is more important than WOT. In fact, WOT DEPENDS on how good part throttle is. Partly because we spend so much more time at part throttle than WOT. PT is time and fuel consuming which is why it isn't very commonly done.

[scottfab]

I think Steven Colbert has already copywrited that term.
The ECM goes C/L at that point. I can see it happening w just my WB. Don't need a scan tool. So the stumble is a consequence of the engine control transitioning from O/L to C/L. There are delays built into the calibration which accommodate the stock setup. Change the cams and things move faster becoming somewhat less stable. So the calibration needs to be modified in order to control the motor more tightly in order to control the instability. In doing the tuning I change parameters in order to keep a tighter leash on the motor reaction to inputs. The stock values tend to exaggerate the inputs to a modded motor.
As I have explained at other times, part throttle tuning is more important than WOT. In fact, WOT DEPENDS on how good part throttle is. Partly because we spend so much more time at part throttle than WOT. PT is time and fuel consuming which is why it isn't very commonly done.

This is an interesting and plausible hypothesis . If it is root cause then you should be able to insert a stock chip and replicate the hesitation at the onset of closed loop for the OP at about 125deg.

If not then modding the code to fix a hardware issue may ensue. It is what we used to call "dog chasing tail" of "F-ing the dog". I've seen this happen on this forum before. To keep that from happening ultimately we'd use in incircuit emulator and watch what the code did (equivalent of data logger). Rather that look at our code and say "it can't do that" we'd see what it did then look at the code to see how it was happening. Not the other way around.

I will be watching this thread closely for the actual resolution to the OP's issue. It's not your everyday run of the mill ZR-1 issue :neutral:

[XfireZ51]

Well just came back after loading new bin and startup. It worked. Got passed the 47.75C point and no stumble. Viewing the WB, I could see it stayed in O/L then got in to C/L at about 68C. It went a bit lean momentarily but then stabilized. Overall, warmup went pretty smoothly. Granted its 85F in the garage but that allowed it to warm up faster. I've attached a screenshot of TPRT w the parameters I changed. You can see the stock values as well.
So IIUC, as we see in the screenshot, the threshold for Hot/Cold MAT is set at 4.25C. Above that point, ECM did use 47.75C and now its 57C for the C/L timer, which at cold CTS, will be 50sec. I didn't include one other parameter which is the CTS Threshold for Hot/Cold or 70/29C. Anywhere in between is considered Warm.
I'm assuming that the timer doesn't change once its tripped. IOW, if it starts at Cold that's the timer, it does not change as it transitions from cold to warm for example.

[LGAFF]

For my car, extreme heat the problem is almost unnoticable.....very cold weather is when the car really stumbles

*Bought items to make a new o2 extension....

I have already tried other chips/ECM....problem stays

[XfireZ51]

For my car, extreme heat the problem is almost unnoticable.....very cold weather is when the car really stumbles

*Bought items to make a new o2 extension....

I have already tried other chips/ECM....problem stays


Ok. Knock yourself out.

[GOLDCYLON]

I'd try Dom's tune Lee

[scottfab]

I'd try Dom's tune Lee

I agree, what the heck. Borrow a chip and see.

[GOLDCYLON]

Lee are you data logging ?

[XfireZ51]

Just did a vid of cold start up using calibration changes. First thing this morning where temps were in the 68F range. The issue here does involve the O2 sensors but not because there is a defect or problem. With larger cams and headers, it simply takes the O2 sensor longer to warmup to operating temps, so the 'work around" is to allow the motor to heat up longer using Open Loop. Basically, you delay Closed Loop operation. This also assumes that the basic fuel map and Open Loop enrichment tables are correct.
You'll notice that motor transitions to Closed Loop smoothly w no hiccup. Routine is done by ECM, no use of accelerator.

Sorry if the vid flips around, hopefully YouTube has corrected this.

http://www.youtube.com/watch?v=-JajzQpLUXk

[Franke]

Xfire, got a question. How far down the exhaust header is the O2 sensor as compared to the original position on the stock header on your car? I know the O2's have to get to 600 degrees before they start working. I think that may be why my friends vette won't pass emissions with long tube headers but will pass with stock ones.

[XfireZ51]

Xfire, got a question. How far down the exhaust header is the O2 sensor as compared to the original position on the stock header on your car? I know the O2's have to get to 600 degrees before they start working. I think that may be why my friends vette won't pass emissions with long tube headers but will pass with stock ones.

If he has headers, he needs heated O2 sensors. The stock O2 is positioned prior to the cat, so very close to the exhaust port. I don't recall if its in one of the header tubes or after the merge. My O2 sits in the collector, so probably a foot or so further than stock. One reason to have headers ceramic coated. Any other mods to the motor? Are there cats on the headers?

[Franke]

I did tell him to make sure he has heated O2's and the shop doing the work confirmed that. No other mods done. He also had new cats attached to the collectors but I think they were a little smaller than stock cats. Could be a problem there too especially if they are cheapys. Latest word from him today is they went back to stock manifolds/cats to get him on the road again. Guess that is the end of the story. Too bad as I think with some more work it probably could have been taken care of.

[XfireZ51]

Any update on this?

[LGAFF]

On my issue or the other guys...

Not from me, I made the 02 extensions and have not had time to put it on........puzzling if its the tune, because I did not have the issue last year

Another piece....if you can get to 3K the issue goes away....

[XfireZ51]

On my issue or the other guys...

Not from me, I made the 02 extensions and have not had time to put it on........puzzling if its the tune, because I did not have the issue last year

Another piece....if you can get to 3K the issue goes away....

Is there a need to get to 3000rpm with a CTS of 125F? What am I missing?

[LGAFF]

during its 30-45 seconds of sputtering if you hit 3K, the issue stops...and if you hold the motor over 3K you basically never see the issue

[A26B]

Question Lee.

You stated "Replaced O2 Sensor."
Did you replace one or both?
New or used sensor(s)?
If new, what brand & PN?

This sounds very much like a bad O2 sensor that is shorting during warm-up. A shorted O2 sensor on one bank will make the engine run terrible in closed loop, but runs OK in open loop above 3,200rpm (I think that's the transition??).

[LGAFF]

AC delco....I replaced the P/S based upon the drop I was seeing on the Tech 1

When I change the O2 harness I will also change the D/S and see what we get

[A26B]

AC delco....I replaced the P/S based upon the drop I was seeing on the Tech 1

When I change the O2 harness I will also change the D/S and see what we get

Why are you changing the harness? Too short?

[XfireZ51]

Question Lee.

You stated "Replaced O2 Sensor."
Did you replace one or both?
New or used sensor(s)?
If new, what brand & PN?

This sounds very much like a bad O2 sensor that is shorting during warm-up. A shorted O2 sensor on one bank will make the engine run terrible in closed loop, but runs OK in open loop above 3,200rpm (I think that's the transition??).


Jerry

Lee says the car runs fine in C/L once he gets beyond the 47C temp.
I just don't see a short being that exact or discriminating.

[LGAFF]

I need to check the continuity on both the extension and the ECM harness....I am wondering if I pinched or damaged something when installing the engine

Why are you changing the harness? Too short?

[XfireZ51]

during its 30-45 seconds of sputtering if you hit 3K, the issue stops...and if you hold the motor over 3K you basically never see the issue

That's because the exhaust gases are getting hotter faster, the mixture is richer, and the O2 is lighting up quicker. Not sure this indicates anything other than O2 needs more heat. That's why it's worse in the winter.

[LGAFF]

Changed the harness
Changed the DS o2

Will find out tomorrow.....

[LGAFF]

No issues today, I would like to see a few more successfull cold starts before declaring victory.