Was wondering what the fuel pressure and spark plug gap would be on a 1991 mustang 331 stroker,gt40 intake,gt40 heads,75mm throttlebody, x 303 cam, powerdyne supercharger 6 psi,shorty headers, and I can't recall the injectors, and I have a fmu. and does it make a difference.Thanks
I take it that you bought the car with the options on it and didn't build it yourself.
The FMU should add 1 psi fuel pressure for every 1 PSI of boost. The fuel pressure setting directions are given below. Use the stock 37-41 PSI range as long as you have the FMU.
Most smart guys ditch the FMU and use larger injectors and a custom dyno tune burned chip.
Spark plug gap should run .025 to .035. Try a wider gap first and see if the spark blows out at high RPM. The wider gap will usually help with idle, fuel economy and low to medium speed performance.
Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 37-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.
Exactly as above. I would like like to see you gap the plugs around . 035. I gap mine to .023 but that's with 32 lbs of boost.
Do you have an aftermarket ignition box in the car?
You are correct I bought it like this and very new to the mustang world. And no there is not a msd box or anything was thinking of getting one do you think that will help.There is a FMU on it and I have a gauge where I can see to adjust it. thanks guys