1991 Z28 5.7L running rough after approx. 5min. - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

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post #1 of 4 (permalink) Old Sep 23rd, 02, 08:56 AM Thread Starter
Join Date: Sep 2002
Location: Diamond Springs, CA
Posts: 4
I have 1991 Camaro Z28 5.7L with stage 2 performance chip, headers, new engine, etc. It has been running perfect since I purchased the car new in 91. But a couple of days ago while driving the car all of a sudden it started to run very rough and almost no acceleration. It acted similar to when you disconnect the ecm bybass connector, but it is not that, that makes it run worse. There is no check engine light. After shorting the A and B pins to get the computer codes it flashes the initial "12" code for handshaking then continues the 12. If there is no problem should the flashing indicator stop after 3 repititions, or does it continue? If not, does this mean that my speed signal sensor "code 12" on the tranny is bad?? Also after letting the car sit for a while, possibly cooling down as well, it goes right back to working fine again until another 5 min. of driving or so. Please give me some advise as to what to try next.
Thanks in advance!
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post #2 of 4 (permalink) Old Sep 24th, 02, 12:43 AM
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Join Date: Sep 2000
Location: Va Beach VA
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Welcome to the club!!! Lot's of good people & info here.

Code 12 means the ECM is working good. It will flash the code 3 times, THEN pause, then move onto the next code if one is stored. Repeat the next code for 3 times, then pause, then repeat the next code, and so on.

I would do a couple things here,
1. Disconnect the battery for 5 minutes and start over. Reset the ECM.
2. Replace the Stage 2 chip with OEM chip and observe the results.

It could be the EGR system leaking when hot. Could be the plug wires bad or ignition coil overheating. Aftermarket chips do make for a little more dwell time on the coil and this does tend to overheat them. You might stop at Radio Shack and get a cap of freeze mist and next time it happens, spray the coil.

Maybe others here will expundge their knowledge...

Everett 68/350/PG/11.90/115mph
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post #3 of 4 (permalink) Old Sep 24th, 02, 02:05 AM
Join Date: Sep 2002
Location: Columbus, Ohio
Posts: 5
The most common thing normally forgotten.

Change the fuel filter!! Everyone buys "goodies" for their engines and blames them first. But for the money look there first than do the chip swap. Keep us posted on where you are at on repairs.

How many miles on this??
Can you check fuel pressure??

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post #4 of 4 (permalink) Old Sep 26th, 02, 06:26 AM Thread Starter
Join Date: Sep 2002
Location: Diamond Springs, CA
Posts: 4
I was able to resolve the problem with Everett's advice on the EGR system. It turned out that there is a device located
next to the distributor(passenger's side) that has two small vac hoses going to it from some diaphrams under the plenum. I believe it is also linked to a temperature switch located there as well. It had a small crack on it where the tee enters the device that it is mounted to. When the temp. reached a certain point somewhere around
160-180 deg. or so, the temp. switch must have engaged and the leak must have caused the issue I mentioned. It was a wierd one, I never had a problem with this system before on any car.

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