I have a 91 Z-28. Now the probs i'm having is it just started to do it all of a sudden. It has no power, misses really bad while driving and when it idles sometimes backfires. But the wierd part is that it runs pretty good for the first 5-10 min, after that it starts to do it. I am getting a code 32 which is either my EGR which I have gotten codes from before but it also could be a defective ECM. Do you guys have any ideas as to what it is, or how I could tell if the ECM is bad? Thanks

 

You stationed over in Europe?
I'd check your fuel pressure, maybe change the fuel filter. If that turns out ok, and you've done a tuneup in the not so distant past, it's possible the EGR valve is sticking open. Double check the timing if you've done a tuneup, maybe the distributor moved. Also possible it could be a bad HEI module or pickup coil if other checks don't reveal anything.

 

When the engine is cold, it is in "open loop", and the EGR valve is not opened by the ECM. After 5-10 minutes, it will go "closed loop", and that may be when your troubles start because the EGR valve is now being exercised. Most likely, it is sluggish and sticking open.

 

I have alot of modifications on this thing and the egr code is always there because of the high flow rate of the exhaust. It has not been touched since I redid the motor last, just started to act like this. Would a bad oxygen sensor make it do this? that could explain why it heats up and runs bad. If it was the ignition problem it would do it all the time right?

 

Tim,

Time to clean up that old stockpile of Mavericks and PaveWays, eh?

If your ignition has failing components, it might not always manifest itself when cold. Some electrical/electronic problems are aggrevated by heat, like weak coils and HEI switching modules.

The EGR would be a good thing to investigate, if for nothing else than to eliminate it as a possibility. The EGR solenoid itself can also leak through, so while the valve can be good, the system may not be. The easiest thing to do is to cap the vacuum line and see if the problem continues. You'll likely set an error code doing this, but since you already have a '32', it really doesn't matter.

If the problem persists with a disconnected EGR vacuum source, start looking at mixture control. Open loop mode on start up is usually on the rich side, so that may be a hint. If the O² is weak, the mixture would get even more rich in closed loop. Your fuel mileage, tailpipes, and spark plug condition should be good indicators of that.