djm_e22

My car starting running like crap and my air/fuel gauge starting leaning out pretty bad. When I have my car at idle fuel pressure is at 47psi, but when I simulated WOT by taking the vacuum line off the FPR it went up to 52psi. Is this correct or is my FPR bad?

Injuneer

Pressure is higher than specification (41-47psi with no vacuum compensation, 43.5psi preferred), which would make it run rich, not lean, at least until the long term fuel corrections started to pull down the calculated injector pulse widths.

djm_e22

That makes since, but do you know why my pressure would go up after taking off the vacuum? or is that the way it's suppose to act. Also could my oxygen sensor that hooks to the PCM be going bad? This could be coincidence but about a month ago I was driving in heavy rain and my air/fuel gauge starting leaning out and its pretty much did it ever since. It will start to run lean then go back to normal and it will do this several times while I'm driving. Also it seems alot of times if I get close to WOT it will go back to normal air/fuel ratios.

Injuneer

The vacuum line is there to compensate for the manifold vacuum. The injector needs to see a constant 43.5psi difference between the fuel rail pressure (what you see on the gauge) and the other end of the injector in the intake manifold. As manifold vacuum increases, the rail pressure has to drop, to hold the constant DIFFERENTIAL pressure across the injector. Hence, when you remove all vacuum reference, the rail pressure should rise to 43.5psi.

You pressure seems a bit high. Is it a stock FPR? .... an aftermarket adjustable FPR? .... possibly an Aeromotive LT1 AFPR? What are you running for a fuel pump? Takes an awful lot of fuel flow before the stock FPR can't control the pressure where its suppose to be.