What are the effects of running too high of a fuel pressure? My FP is currently set at 42psi at idle and 50 or so at WOT.

I will be fixing this tonight by adjusting my AFPR to get it down to 37 but i'm curious as to what, if any, negative effects it would have on the car.

 

You should keep your fuel pressure at the stock 43.5.

If you run too much, the PCM will try to compensate some but it might not cover all of it. As a result, your car will run richer due to injectors flowing more. You might lose some power if you were dead on with 43.5 or you might gain some power if you were a little lean before.

 

Ion - thanks again man!

Is that 43.5 at idle then? I'm hearing that I should drop it to 37psi at idle and around 44 at WOT.

 

Yea, WOT should be ~43.5. As far as I can remember, mine stayed the same for idle and WOT even without an AFPR, but I could be wrong. Anyway, 43.5 is where you should be at WOT.

 

Sounds good sir - thanks again for the help!

 

At idle, the fuel rail pressure (what you see on the gauge) should be lower than at WOT. The correct way to check the pressure is to start the car and let it reach stable idle. Pull the vacuum compensation line off. Pressure should be between 41-47psi (43.5 is the exact, preferred pressure). Then reattach the vacuum compensation line to the FPR. Rail pressure should drop proportional to intake manifold vacuum... might drop 8psi with a stock cam, might only drop 3 to 4psi with something more radical. Then take it out on the road, and at WOT/max HP the pressure should hold within 1 to 2psi of the "no vacuum" number you got.

Running the system at 50psi (no vacuum) causes the injectors to flow 7.2% extra fuel, compared to what they would flow at 43.5psi. That could be a problem. The PCM is capable of pulling about 15% extra fuel with the long term fuel corrections, and more with the short terms. But when the BLM's are below 128, and the PCM is "reducing" fuel, it will run fine in closed loop. But when you go WOT, since the PCM was reducing fuel, the BLM's will return to 128, and you will be putting in the 7.2% extra fuel. Whether that hurts you depends on how well your engine was tuned. If PE tables have been altered to lean out the A/F ratio, and the numbers were based on a data log showing the A/F ratio with the fuel system running at 50psi, you might have just the right tune. But if it wasn't tuned that way, as Ion says, you have to get the pressure back down to 43.5psi. I would assume that he assumed you were running 43.5psi, and tuned it that way (if he did your tune).