91 ZR-1 Cutting Out Under Load - Page 13 - ZR-1 Net Registry Forums

gbrtng · 02-13-2009

My experience with a bad ECM: 2 or 3 unrelated error codes would set. As soon as the check engine lit, the engine would barely run or just stop and not restart. I could not isolate the problem to heat soak because it would happen at any outside and underhood
temperature. Replaced several ignition components with no change. Corey hooked up his Tech 1 and left baffled after an hour. I finally decided to change the ECM and yep, that was the problem. This was on Mary's 91 L98 which uses a common junk yard ECM - I was able to score one locally for $55 - which crosses to about 10 other GM vehicles.

XfireZ51 · 02-13-2009

Quote:

Originally Posted by gbrtng

My experience with a bad ECM: 2 or 3 unrelated error codes would set. As soon as the check engine lit, the engine would barely run or just stop and not restart. I could not isolate the problem to heat soak because it would happen at any outside and underhood
temperature. Replaced several ignition components with no change. Corey hooked up his Tech 1 and left baffled after an hour. I finally decided to change the ECM and yep, that was the problem. This was on Mary's 91 L98 which uses a common junk yard ECM - I was able to score one locally for $55 - which crosses to about 10 other GM vehicles.

L98's had a well documented issue with ECM. Something about the board material being a bit flimsy and the circuits developing micro-cracks.
I'm in the "innocent till proven guilty"

camp when it comes to an ECM causing the kind of issues being discussed in this thread.

GregCrowe · 02-13-2009

Jeff tends to think 75-80% chance it's a coil problem, 20-25% chance it's the ECM. Taking bets on what it is

If it's either of the 2, I'll have it fixed in not too long.

Then I get to take the car up to the tag agency and explain to them why it hasn't been tagged in 3 years......... LOL.

XfireZ51 · 02-13-2009

Quote:

Originally Posted by GregCrowe

Jeff tends to think 75-80% chance it's a coil problem, 20-25% chance it's the ECM. Taking bets on what it is

If it's either of the 2, I'll have it fixed in not too long.

Then I get to take the car up to the tag agency and explain to them why it hasn't been tagged in 3 years......... LOL.

Given those 2 choices, I'd pick coils altho I'm not convinced it's that either. I wouldn't be doing anything until I had a scan. With all the time that has gone by, there should have been a way to connect a scantool to this motor.

LT5-Lee · 02-13-2009

Quote:

Originally Posted by GregCrowe

Jeff tends to think 75-80% chance it's a coil problem, 20-25% chance it's the ECM. Taking bets on what it is

If it's either of the 2, I'll have it fixed in not too long.

Then I get to take the car up to the tag agency and explain to them why it hasn't been tagged in 3 years......... LOL.

ECM, wiring or MEM-CALl. Some corrosion somewhere.

LT5-Lee · 02-19-2009

Quote:

Originally Posted by GregCrowe

OK, in complete detail:

When the car is cold or even just warm and being driven for the 1st 15 minutes, no issues whatsoever, even with full throttle. After the car has been driven and has sat, heat synching the engine, the miss begins. Normal driving with light throttle, no issue. When a load is applied, the miss begins. The miss is very "electrical" feeling. It does not come and go under heavy fuel delivery situations. It's just a very quick electrical miss and shudder. The car never dies nor does it even come close to dying. Again, it's only under medium to heavy load. If you want to make it miss the absolute worst, let it heat synch and then bog it down in a high gear at low speed and floor the gas. Then the car will shudder and jerk. If you try to accelerate through the gears at full throttle, the car just plain misses like it has 2-3 bad plug wires arching.

Greg, I think I found my gremlin..=D>

and I can't believe what it turned out to be. I was wiggling everything while the engine was idling and for the hundredth time, I played with all the sensors and then the MAP sensor and the engine died? I swear I checked it out many times, but it seems the rubber accordion seal on the connector must have gotten twisted and was not quite snapped on tight. My scan tool showed the correct voltage readings, but I guess when the engine torqued just right it lost connection?

I can not believe it because it was one of the first things I suspected and always made sure it was tight, but I had to squeeze it so hard before I heard the plastic snap, I thought I was going to need some channel locks before I actually heard it snap on!!!

I maybe a little premature as I have only made a few hard runs for testing it out because of traffic, but knock on wood, I hope I got it!

After doing some data logging I probably have some other issues that made it worse, like a lazy LH o2 sensor with low cross counts (or a really slow scan tool "Auto X-ray"),but I am preying the MAP sensor connector was the major problem. My problem wasn't just heat related, but it chugged so bad it felt like it would throw you into the windshield just like you described so I thought I would just pass along my good fortune just in case?

XfireZ51 · 02-19-2009

"My scan tool showed the correct voltage readings, but I guess when the engine torqued just right it lost connection?

"

If you had put the scan tool on and datalogged while driving, I'll bet you would have seen the MAP voltage drop under load.

GregCrowe · 02-19-2009

Quote:

Originally Posted by LT5-Lee

Greg, I think I found my gremlin..=D>

and I can't believe what it turned out to be. I was wiggling everything while the engine was idling and for the hundredth time, I played with all the sensors and then the MAP sensor and the engine died? I swear I checked it out many times, but it seems the rubber accordion seal on the connector must have gotten twisted and was not quite snapped on tight. My scan tool showed the correct voltage readings, but I guess when the engine torqued just right it lost connection?

I can not believe it because it was one of the first things I suspected and always made sure it was tight, but I had to squeeze it so hard before I heard the plastic snap, I thought I was going to need some channel locks before I actually heard it snap on!!!

I maybe a little premature as I have only made a few hard runs for testing it out because of traffic, but knock on wood, I hope I got it!

After doing some data logging I probably have some other issues that made it worse, like a lazy LH o2 sensor with low cross counts (or a really slow scan tool "Auto X-ray"),but I am preying the MAP sensor connector was the major problem. My problem wasn't just heat related, but it chugged so bad it felt like it would throw you into the windshield just like you described so I thought I would just pass along my good fortune just in case?

Congrats, hope that's all it is. That can't be my problem. I've had the plenum off and MAP disconnected multiple times during this ordeal. Just got Jeff's spare ECM in (weird part number: 16148441). Going to give it a try Saturday.

LT5-Lee · 02-20-2009

Quote:

Originally Posted by XfireZ51

"My scan tool showed the correct voltage readings, but I guess when the engine torqued just right it lost connection?

"

If you had put the scan tool on and datalogged while driving, I'll bet you would have seen the MAP voltage drop under load.

I did, and it followed the throttle angle/voltage and engine RPM closely under load so I thought it looked fine, It idled at 750 RPM with 1.37v and at 0 rpm it read 4.84v EOKO. It did loose voltage about the time the secondaries should kick in so I figured that's about right (3300 rpm) with the drop in vacuum. Maybe I still have a grounding problem and just being fooled?

I still want to check all major grounds for grins and need some more practice and experience in diagnosing the sensors. Right now it sure looks like something is wrong with my o2 sensor.

Greg, all I am trying to say is did you hear it snap on, or did you just figure it has to be since it survived a death grip?

XfireZ51 · 02-20-2009

Lee,

MAP sensor going to 0 v when opening
the throttle is the opposite of what should have been happening. That's the clue a scan can provide. It didn't last long enough to throw a code but it affected your throttle response

02-13-2009	#121
gbrtng Join Date: Feb 2006 Location: San Antonio area Posts: 1,179	Re: 91 ZR-1 Cutting Out Under Load My experience with a bad ECM: 2 or 3 unrelated error codes would set. As soon as the check engine lit, the engine would barely run or just stop and not restart. I could not isolate the problem to heat soak because it would happen at any outside and underhood temperature. Replaced several ignition components with no change. Corey hooked up his Tech 1 and left baffled after an hour. I finally decided to change the ECM and yep, that was the problem. This was on Mary's 91 L98 which uses a common junk yard ECM - I was able to score one locally for $55 - which crosses to about 10 other GM vehicles. __________________ “Buy the best example of what you want, and pay whatever it takes. That way, you cry only once.” ~ Bruce Meyer

02-13-2009	#123
GregCrowe Join Date: Sep 2004 Location: Oklahoma Posts: 111	Re: 91 ZR-1 Cutting Out Under Load Jeff tends to think 75-80% chance it's a coil problem, 20-25% chance it's the ECM. Taking bets on what it is If it's either of the 2, I'll have it fixed in not too long. Then I get to take the car up to the tag agency and explain to them why it hasn't been tagged in 3 years......... LOL.

02-19-2009	#127
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,698	Re: 91 ZR-1 Cutting Out Under Load "My scan tool showed the correct voltage readings, but I guess when the engine torqued just right it lost connection? " If you had put the scan tool on and datalogged while driving, I'll bet you would have seen the MAP voltage drop under load.

02-20-2009	#130
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,698	Re: 91 ZR-1 Cutting Out Under Load Lee, MAP sensor going to 0 v when opening the throttle is the opposite of what should have been happening. That's the clue a scan can provide. It didn't last long enough to throw a code but it affected your throttle response Last edited by XfireZ51; 02-20-2009 at 08:29 AM.