Thanks for reading my post!

My 86 Z28 5.0 TPI seems to be "missing" and bogs down until it runs for about 5 or 10 minutes. I changed the plugs, wires, cap, and coil. Same symptom. Any thoughts? Could this be an Injector, Catalytic converter, O2 sensor? Would appreciate your thoughts and advice. THANKS!!!

 

Hello Looksthakill!!

Try changing the coolant temp sensor at the front of the intake manifold, this is the one that tells the ECM what temp your coolant is at, and then controls your engine settings based on that reading!!

A faulty one gives you the symptoms that you described above!!

Also check that your EGR valve is free to move, and is not binding/sticking!!

 

Thanks for the response. I will replace that sensor...

 

i had the same problem, if the temp sensor is not hooked up or bad it reads like -40 degrees or something and dumps all kinds of fuel in. i have never seen spark plugs so fouled up in my life, holy buckets.

 

Darn sensors!!

 

Wouldn't the EGR valve only affect starting of the car?

 

Okay just did this. I had a bad injector on number one which missed and ran crappy till it warmed up to operating temp and went to close loop and then it made the rest run a little rich. put in 8 bosch 3 from southbayfuelinjectors and idles steady and runs like a champ. this is a 91 tpi setup in my 92 chevy pickup.

one way i narrowed it down was unplugged injectors one at a time and one did change much if at all. and also header temp at one was 260 and all others were between 500 and 550

 

Hello New2Chevy!!

I just mentioned it so that it can be ruled out!!

If you start your car, and then apply some EGR it will run crappy, that's why I said to check it for binding/sticking!!

 

Hello Looksthakill!!

Let us know what the outcome is!!!

 

Thanks for the responses guys. I also pulled the SES codes. I am getting 33 and 36. Reset the computer...same codes. I need to do a bit more troubleshooting, in addition to replacing some of the usual suspects. So far I have been pointed to the coolant temp sensor on the front of the intake manifold, the MAF power and burnoff relays, and possibly one or more injectors. Let me know if any other thoughts. Cheers!

 

An update...I replaced the MAF burnoff and MAF Power relays, as well as the engine coolant temperature sensor at the front of the intake manifold, and guess what? The error codes disappeared from the SES, and the light is NOT coming on! Woo hoo! It is definitely running better.

HOWEVER, the car is harder to start now. Sometimes it will fire right up, other times I have to CRANK and CRANK. It seems inconsistent so far. Does not seem to matter if hot or cold. I am thinking that I should adjust the timing and the IAC. What do you guys think???

Thanks again for your input!!!

 

Hmm......adjusting IAC and timing would be a good place to start....sounds like the egr, but that should pop a code. Let us know.

 

Thanks, I am going to start there, with the timing and IAC. Also need to check my injectors. I believe that the resistance should be checked when they are hot and cold. They LOOK like the originals, but I am not certain. Will let you guys know. thanks again, and do share any other thoughts, if you have them!

 

Except for your "does not seem to matter if hot or cold" statement, it sounds like the Cold Start Injector(often referred to as the "9th injector," used from '85-'88) isn't firing. Its "switch" is the "sensor" right next to the Coolant Temp Sensor on the front of the intake manifold. Is it possible you disconnected it when you replaced the CTS and simply forgot to re-connect it?

The Cold Start Valve(the injector, itself) is located at the base of the intake runners on the driver's side, between the pairs of runners. I don't know if you've been working in that area, but if you were disconnecting fuel injectors, might you have disconnected this one too and overlooked re-connecting it?

None of this should matter when the engine is hot though, but I'm mentioning it anyway, just in case...