I need help with my friends 87 iroc. We replaced every sensor when we put his new motor in. It is now a 355 with my old slp runners,tpis base, 52mm throttle body, stock heads pocket ported, 24lb injectors ,LT4 hot cam, mac headers and cat back. Ed write did the chip for the bigger combo. Our problem is at idle the car is putting way too much fuel into the motor. Then when you try to give it gas the motor just breaks up. We just had it on the dyno this morning to get some info out of the computer and everything was with in its limits. The only thing we can think of is the computer or the non "gm" mass air unit he bought at advanced auto. please help

 

I would check for a ground problem. The reason I say that is you said when on the dyno everthing was in specs. The ground on the back of the block pass side is easy to not get tight. If not that I would do a tap test on the ECM and MAF sensor. Some times you can tap on them with your hand and they will stall the engine or make it run rough. Back in 87 I worked for Buick and when a GN would come in with a running problem that is the first thing we would do. After that we would check the crank sensor and cam sensor. The MAF and ECM would turn up alot.

 

Did you check the fuel pressure at the regulator?? And what was the air/fuel ratio from the dyno run???

 

Fuel pressure at the regulator is 45psi. A/F ratio was 12.2 at full throttle but that is the least of our problems. It is just putting way to much fuel in at idle. A/F ratio from the dyno is not accurate when not under full power. At least that is what I was told. We will go back over the grounds again but we will try tapping on the computer and maf.

 

Just a longshot before you do anything drastic, try changing your chip out for the stock one and see what happens. The Maf should not be dumping fuel.

 

We did that and it made it very,very,very bad.
Thank you anyway We need all the help we can get!!!

 

Have you checked the idle circuit injector. It could be stuck open.

Please disregard. I beleave only the Corvettes had this???

 

I had the same problem with my 87 Z. I found out what mine was, I changed the base intake and the injectors on my car and the thing was getting to much gas at idle, when you go to drive the car it was ok and it got really crappy gas mileage also. I searched for about two days and found out that when you change the base intake and the injectors you have got to make sure that they are perfectly centered and not to tight. One of my injectors was to tight and was grounding itself out on the intake and staying open at all times. Just check this and see before you start going into it deeper and replacing things. I have heard of this happening alot lately on TPI motors. Let me know if that was it or what you find.

 

Thank you We will try this as soon as we can. He let his car sit outside and now we can't get to his garage because of snow. I'll let you know how we make out when we get a chance.