Mikey97Z

Before my heads/cam install, my fuel pressure was always at 41psi, and went up to about 48 at WOT.

Now, after installing my XE230/236 cam, my manifold pressure is a lot higher at idle (60kpa) and low rpms than it used to be, and it's causing my FP regulator to raise the pressure too high when it's not necessary. My LTerms are bottomed out at 108 in some cells.

I have a couple of questions for some smart guys:

1) Why does the fuel pressure need to be changing according to manifold vacuum? Why can't it just remain constant?

2) Which would be the best way to correct this? Increase the injector constant, or install an adjustable FPR?

Thanks.

Rodrigues

you really need a professional tune with your cam.

Buttercup

1.) The fuel pressure changes but the flow should remain the same. Flow rate is determined by the pressure differential between the rail and plenum. If you have high vacuum you don't need much fuel pressure, as the engine is basically trying to suck the fuel in. Under low vacuum, such as WOT or idle with a larger cam, more fuel rail pressure is required to flow the same amount of fuel. All of this is the job of the FPR and it is required on our cars as the PCM uses a fuel flow constant On a side note, LS1's do not use this type of fueling, their PCM understand different flow rates.

2.) If the condition only applies at idle you may want to change the injector offsets. Changing the injector constant will have more effect over the entire RPM/load range. You can also try tweaking the MAF frequency table.

48psi is on the high side for no vacuum btw.