1slwgto

iTrader: (3)

Okay so the truck is a 99 with a pro charger , cam , worked heads. I've had the truck tuned and it was running great then all of a sudden one day it started getting high fuel pressure 80 + psi . So I was told it might be the fmu . Toke that off seemed to fix it . Then started getting a little low fuel pressure so I put in a 255. Did a little better but now it will range from 28 psi to 80 psi when just driving and my fuel trims are all over the place when watching them .
I do have 60 # injectors also but everything else is stock for fuel. I've read that the 99 you can use the stock fpr since it runs off a vacuum reference on the fuel rail from the intake manifold.

Any help would be great before I go replacing stuff I don't need to yet .

DrX

iTrader: (7)

Sounds like a bad FPR What's the fuel pressure key/on engine/off, and does it hold when switched off? Any fuel leaking from the FPR into the vac reference line? Should not go to 80 psi unless you are at 20 psi of boost. .

1slwgto

iTrader: (3)

When its key on ( no start) it comes up to 40psi . Once truck is started it goes up like 42psi. At lease that's what it did just now. FPR was just replaced ( with another stock one ) . Also no fuel is leaking . But I also just noticed the truck also has a inline pump on it . So I'm going to take that off as well . Also how much have y'all seen a 255 support up to ? I read different specs every where for it . Asking because I will be putting a 75 - 100 shot along with the p1 in the form of a plate kit.
Thanks again for any help .

1slwgto

iTrader: (3)

Well I toke of the extra fuel pump and even replaced the fpr again just to make sure. But my fuel pressure will start at 30ish psi then slowly creep up to 90 100ish psi. Anybody have clue what it could be?

DrX

iTrader: (7)

Blocked/pinched return line?

What is the pressure with the vac reference removed from the FPR? Should be around 60 psi. What kind of fuel pressure gauge are you using?

1slwgto

iTrader: (3)

I was thinking the same on blocked/pinched line . I had to drive the truck home and when on interstate it would very slowly go down to 38 psi . Then once in stop and go would go back to 100 psi. when I've unplugged the vac line off the fpr it would have no change in fuel pressure.
I'm going off my auto meter gauge I have on my pillar .

DrX

iTrader: (7)

My Autometer electric gauge went wonky. I have another gauge on my FPR.

Strange for the pressure to be both too high and too low. Seems that would require a pinched return and an intermittent leaking feed.

1slwgto

iTrader: (3)

I haven't had time to mess with it but I've driven it some this week and have noticed that its staying below 60 psi now. I was having one person tell me that it was in my tune since I had the truck tuned with the fmu and inline pump on it . Do you think that could be the issue ?

DrX

iTrader: (7)

The tune is not going to effect the fuel pressure, but your tune will be off if the fuel pressure is erratic. Should go over 60 psi in boost and under 60 psi in vacuum.

1slwgto

iTrader: (3)

I didn't think the tune would do that but wanted to make sure. I've had it running then toke off the line for the fpr and nothing changed on my fuel gauge . I'm thinking of picking up a diff one and putting it right on fuel rail to see if its just my gauge messing up on me .