I have a 1989 iroc with 48000 miles on it. everything is mint but its running like ****. the supercharger is a paxton and was creating 7 psi of boost. I took the heads off last winter to discover a burnt head gasket between two cylinders. I put it back together with felpro gaskets and it ran fine for a few weeks. the car then began to run rough but only when it warmed up. it would shutter and then the idle would ramp up and down. if i turn the car off it wouldnt want to start again untill it cooled down. i threw tons of parts at it like the throttle positioning sensor mass airflow sensor even a computer and chip but it still reacted the same. So i pulled the heads off last week and discovered that there was no burnt head gasket, everything looked fine. except the spark plugs that i replaced last winter seemed to hang way in side chamber just nearly hitting the valves i found out that they were the wrong length plugs (thanks Napa) but i was told by many people that it wouldnt really matter as long as they werent hitting anything. I noticed that some cylinders were more black than others. so i decided to send the heads out for a rebuild. they came in today and they said they were warped slightly and shaved .006 off. ok so now i have nice fresh heads and the right spark plugs ( which i was told to run 2 heat ranges cooler). but what do i run for a head gasket? will that .006 matter ? I thumbed through summit and saw some $200 gaskets made by SCE that are guarenteed to hold up. Im thinking about buying these. what about fuel injectors i believe mine are stock should i move up to 40 lb injectors? what about a fuel pump i believe it is stock as well. can i add a pump external to the tank and still run my stock pump. what about fuel pressure where am i supposed to be with that while running 7 psi of boost? Im kind of lost but i dont want to put this thing back together and have it run like **** again. Am i going in the right direction? Someone please help me!!!!!!!!

Your Injector size shouldnt interfere with idle. It will make it hard to keep power on at WOT as the injector duty cycle goes to 100% and the engine goes lean, however. 40 lb injectors are too big, IMHO unless you are making 650 HP at the wheels. I'd guesss that 28 to 30 lb injectors will be sufficient.

As for fuel pump, A Walbro 255 lph in-tank from Thunder Racing is the ticket, along with new power and ground wires to the pump.


You need to back up a little and make some measurements.
1) Check mechanical timing to make sure 6 degrees BTC is really 6 degrees BTC.
2) Check fuel pressure to see if its fluctuating. Since you have a boosted engine, if boost jumps up and down, so will fuel pressure.

If it runs rough when warm, perhaps your engine tune isn't good for the new combo. Are you using a stock PCM and chip? It might be unstable in closed loop as the engine surges and goes rich/lean. You might want to invest in a innovative Motorsports LM1 wide band logger. It'll help you figure out what the engine is doing.

I have checked the timing dozens of times trying different combonations i left it set at 6 deg btc. but my fuel pressure i never checked what should it be? It is probably fluctuating. does that fuel pump replace the stock one? is it tough to pull the tank? how nescessary is it to replace the injectors if i currently have stock ones?

I am running a superchip which made no difference when i swapped it with the stock one as far as rough idle pulsation

That surging also doesnt sound likea supercharger problem. Mine and a few others ive messed with have done things like that. Usually its somthing in the timing wiring that goes out. Mine was simply a unseated ECM chip, reaseating it fixed my problem. Also if the voltage to the EST wire fluctuates that could be a problem. I doubt it but it could also be an EGR problem if you still have the system.

maybe the engine temperature throughout driving isn't good ? maybe u should get a lower thermostat say 175..
When u put everything back together get the mixture checked (AIR/FUEL RATIO).