I buddy of mine has a 1992 z28 5.0tpi 5 speed. He recently took car out of storage. I drove it around to check it out for him, and it ran great until 10 minutes into the trip. Then it lost power gradually, until 60 seconds later when it died. Within less than a minute it went from running perfectly, to having no power. It did it gradually, like as if it was losing 20 horsepower every 5 seconds. it got worse and worse until the motor had to be shut off because it did not have enough power to move the car. It did not make any loud noises. Just lost power. The manifolds were red hot when I opened the hood to check it. And it said service engine soon. This never happened before.

Later on he started the car and it was fine, but he won't drive it again until he figures out what makes it die like that. He does not like the idea of the red hot manifolds. The car is totally stock with 30k original miles, and he is the original owner. The ecm had a code, but I can't remember what it was. I remember looking it up and it had something to do with timing or distributor. It may have just been a code that said the timing was too far retarded. That is what I seem to remember. It has been quite a while since this happened. But now I want to try to fix it because the guy has to move the car to another location. The only problem he ever had with the car before was a misfire which was traced to a plug wire shorting out to ground. I wonder if this short could have caused some electronic aspect of the ignition to wear out prematurely.

My question is, what could be causing this. Do these cars somehow control timing advance or retard with the computer? How do these cars control the advance or retard? is it the ecm that controls it? the ignition module? Never had trouble with a car with a distributor AND a computer to control timing. I don't know how it advances or retards the timing. or why or when. is it a set map or does it respond to a knock sensor and so forth.

I am gonna try to fix this car. Are there certain parts I could buy and replace that would cure this timing issue? There can't be that many parts that control the timing. I already happen to have a new ecm. What else would I need? is there a pickup, a module, and any other items that are involved in this? It seems strange that it is an intermittent problem. Must be something electronic. it is strange that it would mess up the timing so bad that the car would stop running. If he was to upgrade to an accel or msd setup, would that eliminate this problem? Or would there still be some aspects of the old system in control of the timing.

Thanks for any ideas. I will try to get the code number that the computer gave when it said service engine soon.

 

Sounds like somebody was twiddling with thetiming for whatever unknown reason, and left the dist is loose; and the timing is now at about 45° retarded.

Grab the dist and just advance it about that much (22½° of dist body motion = 45° of crank motion) and see what happens. If that makes it run right, put it back where it belongs, tighten the bolt, and tell him to leave it alone FOREVER unless it gets disturbed. It doesn't need routine maintenance; it never changes unless disturbed.

Codes won't help. The ECM has no way of looking out there and seeing where the dist body is located. There's not one for "too far retarded".

If it doesn't fix it, put it back and try the next thing.

 

It's not the position of the distributor. We checked on that after this happened. After the car cooled off, it was back to normal. It was tight and it had the correct timing at idle with the timing light. This is an intermittent problem.

 

Well without knowing what the code is theres not much I can do. To answer one of your questions yes the ECM does control the timing. The code I believe your refering to has to do with the electronic spark control system. Essentially what it does is tells the ECM to retard the timing when it detects a knock and to keep retarding it untill no more knocking is detected. Eventually however the ECM gets to the point where is says ok what the heck ive retarded the timing like a 1000 degrees and the cars still detecting knocks??? The ECM figures something must be wrong and throws a code.

 

You ARE disconnecting the ESC plug when you're setting idle timing right? If not, then every time you adjust the timing, the computer re-adjusts it to the correct range. Your indicated timing is going to be correct, but your actual base timing may be way off.

 

While your at it check the catalytic converter it could be clogged completely I had the same problem with my 86 z 28 and after replacing everything the mechanic told me too I checked my cat and sure enough it was clogged to the max this could explain the red hot manifolds

 

i agree. over retarded timing. that loss of power is the motor getting ready to blow up. soon youll hear that knock, knock, knock sound, if not corrected.

 

thank you guys this is very helpful. It is not the catalytic converter, or the position of the distributor.

Apparently the computer is retarding timing to the point of respiratory failure and cardiac arrest. So the question is why is the computer doing this, and why does it only do it sometimes?

Can this ESC be disconnected for diagnostic or limp home purposes? In other words, is there some wire that could be disconnected to disconnect the ESC system but would still allow the car to run? Would this be the same wire that you disconnect when checking timing at idle? Could you drive the car like that? (sure it would throw codes but at least would not ruin the motor and stall the car like the 1000 degrees retarded timing.)

Besides that, I guess I should read the shop manual to find out the diagnostic procedure for a car that retards timing for no reason.

I guess it thinks there is knock when there is none. There is definitely nothing unusual going on that would set off the knock sensor. (I mean like metallic rattling sounds under the hood, etc.)

Perhaps the knock sensor is faulty?

The intermittent aspect is the worst part of it, because if it is not acting up, there is no test or procedure to fix it. And if it does act up, you need a tow truck and you are stranded.

Maybe we will change the ecm, the knock sensor, the esc module, and whatever else is in there related to this system, and hope for the best. We could probably buy all the parts for less than one towing bill. we already have the extra ecm anyway.

 

It's the same wire should be tan in color

 

Makes me glad I dont have fuel injection... the headaches when it doesn't work right. That said the benefits are amazing, I miss it, but not when I hear stuff like this.

Anyway, if you're disconnecting the ESC wire to set base timing (6 degrees IIRC) and your base timing IS actually correct, I would try one other thing before disconnecting the ESC. That would be another way to get home I guess, though. Might want to experiment, but no 20 mile drives like that until you know what it does.

Anyway, if it's super retarding the timing, the knock sensor could be telling the ecm its hearing knock, and the ECM is retarding the timing into oblivion. That in itself could be cause for alarm - why is it hearing noises? But I would disconnect the knock sensor for diagnostic purposes when it does this. The knock sensor is in the middle of the block right above the oil pan rail. Cant remember which side it's on, though. but there will be a plug on one side and the knock sensor on the other. If you pull the knock sensor the computer will throw a code, and then ignore the knock. I dont know enough about TPI to say whether it would go into limp home mode or just throw a code and go on with it's business or what, but it's another thing to try.