I have a 90 coupe with a 331 f-p-s motor in it. Car is sputtering sometimes. Won't go clean up the rpms. Sometimes it has the problem and sometimes it runs perfect. Mods incl. vortech v1-s-trim, trick flow heads, etc. no aftermarket ignition. changed cap & rotor, coil, etc. Sounds like a missfire when driving. can also smell fuel sometimes. Also, the fuel pressure gauge shakes like its nervous, instead of holding still. 42lb injectors and 255 intank t-rex inline. Any help would be aprreciated. thanks. the black and white harness behind the intake, if moved, sometimes changes the idle of the car.

 

Did you try your fuel filter? Could be clogged....causing the run perfect/bad combo on days.

 

have you had any detonation, also if your air filter is mounted under the hood you could try to install it in the fender, this would prevent any fan wash! wich could cause you to heat up faster and lose performance...

 

thanks for the advice. We found the problem, it was a blown headgasket. We checked the compression and the #8 cylinder didn't hold. Pulled the head off and the gasket in between the cylinders was gone. Not at the water jacket so no loss of water. we'll see how it goes. I'll repost the results. Going with chromatic gaskets now. Don't get caught without them!