I've got a 1995 Formula Firebird with LT4 heads, LT4 Intake, custom grind cam, long tubes, Borla Cat-back, MSD, 52mm throttle body, etc...

I was curious how much fuel pressure I should be running. I have an adjustable fuel pressure regulator, and the car has like 36-37lbs right now at idle. It just seems stupid rich to me, but thats what the guy I bought it off said he ran it at.

Any input?

Any help would be greatly appreciated.

Thanks,
Wes

 

Wes If your running the stock computer program the car will seem a bit rich mainly during cold starts and open loop modes. Not knowing your head and cam combination specs assuming you are making 350 to 400 fwhp and running the stock 24lb injectors your duty cycle at 38psi will probably be pretty high. Best thing to do would be upgrade to 30lb injectors and custom tune. If you want to stay with the stock injectors I would think about 45psi fuel pressure would be a good place to start. But regardless as long as you have stock tuning the car will seem rich. Hope that helps.

 

How did you measure the fuel pressure at idle? With the vacuum line on or off?

Stock pressure reading with the vacuum line disconnected is 43.5psi +/- 2.5psi. When you attach the vacuum line, the fuel pressure will drop proportional to idle vacuum... maybe 6-8psi with a stock cam, and 4-6psi with something a little more aggressive.

If you are reading 36-37psi at idle with the vacuum line on, you should be OK to about 400HP. Over that it gets "iffy", but that isn't going to cause it to run rich. When do you feel it is "rich" - at idle, low load driving, or WOT?

You need to get a scanner on it and determine what the long term fuel corrections are. If its properly tuned, running at stock pressure with stock injectors, you would see BLM's close to 128. If the fuel pressure was set too low, you would see BLM's well above 128. As long as they don't max out at 160, you shouldn't see a problem. But if your injectors are approaching 90% duty cycle, it would make sense to increase the pressure, and enter the revised injector flow rate into the PCM tuning.