After completing my rebuild/upgrade, I was driving around for about 20 mins when I developed a real bad misfire (seemed fine before that). I assumed that this was due to the two burned plug wires that I promptly replaced and rerouted. When this didnt solve the problem, I replaced the opti, plugs, and checked all the wires. While everything looks in order, I still have a BAD misfire that gets worse as things heat up.

Symptoms include high idle (is this the PCM compensating for rough idle at lower engine speeds?), and a huge stumble/stall under load and at low engine speed. I also noticed that five of my primaries are glowing red (lean?), while three of them don't.

I put all new injectors in during the rebuild, and I have never had any fuel related problems before this time.

Any advice/input would be GREATLY appreciated.

 

Did you remove the EGR, if not try disconnecting all that stuff and give it a shot, unless you are emissions regulated, you dont need it. Also check out the O2s. Any codes being thrown?

 

During the rebuild, I removed the EGR valve, lubed it up, and checked it for proper operation. I didn't replace the solenoid yet. It seems that this stumble is way too big to be a vacuum leak. It renders the car almost undriveable, and everything that I have heard about vacuum leaks is that they are more apparent as a small stumble. Also, the idle speed fluctuates especially during initial startup, which would suggest that it is the PCM trying to compensate rather than being fooled by a leak.

I also replaced the O2 sensors during the rebuild.

 

A friend just did a Heads, and Cam, swap and just got his 94 Firebird back together it too would run like CRAP, after it heated up.

We thought Opti, wires, etc...So I brought over the Lap top with TTS installed and hooked his car up, and it turned out that his temperature sensors needed replaced... The car would jump from open, to closed loop and back and forth. When heated up, if the car was in closed loop it ran fine, BUT if it jumped into open loop it would stumble, die, idle poorly, etc.....

I believe that he replaced the 2 sensors, in the head and the one in the block. The guage on the car was fine, but the computer was bouncing everywhere with the temperature readings.

This may be something I'd check

 

Im not completely sure how this works, but I think since it runs fine cold, in open loop, not using the O2s, and the egr is open to warm up the cats and the intake air. Then when it warms up the egr should shut off i think, and the o2s turn on for closed loop. If the egr stays open and dumps exhaust gas into the intake, and the O2s read too much O2 in the exhaust it will cut out a bunch of both timing and the BLMs will drop significantly lowering the A/F below 14.7.

I think this is right, anybody know for sure????

 

I tried starting her up yesterday and she ran bad right from the getgo. Not as bad as when warm, but definately something wrong.

If it was the difference between open and closed loop, then it would be a marked difference between open and closed, right? For me, it's kind of gradual.

I also have a spare ECT sensor laying around, so I'll shove that in there.

Another indicator is that some cylinders are obviously running lean, while the exhaust is obviously rich. I have a feeling this is b/c the O2 sensors have been fooled by a 'false rich' condition caused by the misfire, and the PCM has leaned out the non-misfiring cylinders to make up for it.

I am thinking of testing the PCM by swapping in a 97 Z28 PCM. Any probs with this? I know its OBDII so I may get an SES light b/c of emissions stuff, but how will it do on spark and fuel curves?