1991 Z28 Code 43 & 53
 

The car ran great one day, then sat for a few weeks. When it was started, it immediately idled rough and ran like crap. It was running extremely rich (black smoke). Gave codes 43 & 53. I changed the ignition module...no change. So today I changed the knock sensor (code 43) and reset the computer. It started up and ran perfect....for about two minutes. Then it started running rough like before and died with the same codes. I am at a loss.:mad0259: I'm thinking either ECM or pick-up coil, but usually the pick up coil causes a no spark situation right? I can't figure out why it would run great for a couple of minutes and die. The Code 53 has me baffled too. It has 12 volts off and about 14 running, so I don't think it was overcharging. Any ideas? I would sure appreciate it! My '68 SS is so simple to diagnose. It's usually either something in the distributor or the carb!

Check your EGR valve.

Really? That will give those codes? We have had EGR problems before. Less than 3,000 miles on the last new one and the solenoid is only a couple of years old. We do occasionally get code 32 though.

We had one once that ran so bad with the EGR valve stuck open that the knock sensor was picking it up. That wouldn't explain 53 though. Anything over 16.9 volt will trigger 53. Turn your headlights on and off to see if you can make it spike past that. If your sure the alternator is good, then ECM is bad!

Okay, I'll check the EGR valve with a vacuum pump to make sure it moves. Probably is the ECM though. I'll keep you posted when I figure it out.

It sure points to that! I know that isn't what you wanted to hear, but remans have really come down in price.

I see Advance auto parts has a Reman Cardone, preprogrammed for $60. Can't beat that. For that price, I guy could afford to buy and try!!

Yep, that's what I'm thinking. Even if that's not it (but I think it is) it would be worth it to have one as a spare for that price. Even though it is relatively low mileage low 80k, this would be the first ECM we ever had to replace in it. We've replace injectors, and a whole bunch of other stuff, so this is no surprise. For a car that is in basically showroom condition, it sure has been a PITA!

It seems as though age is a bigger enemy than miles anymore! The older I get, the more problems I have too.

I had crazy probs with my ECMs on the '87 IROC.It would blow black smoke,idle roughly,
Get 11 mpg, smelled like rotten eggs, etc. never once throw a code.
I replaced the ECM 3 times during the 206,000 miles I had it and it fixed the problem every time.
I also had an issue that was similiar when the throttle body went into limp home mode but that was a high idle.

Probably a stupid question, but could the PROM chip be part of the problem or is it usually the ECM? Which one has the ESC module built in?

Out of all the ECM'S we've replaced, I have never had to replace a prom. You should have other codes and or no start with prom problem.

my 91 z28 had about 300k miles on it and in one week i had absolutely everything go out electrically in it. i quickly got rid of it. it was one of the best cars i ever had until that week.... gremlins ugh

Thanks Fishman, that's exactly what I needed to know! As soon as I get the ECM changed out, I'll let you know what happened.