Fuel pressure at idle is about 25 to 27 PSI......
I have upgraded pumps (255's), 50 lb injectors. It was running fine until I went to the track saturday night. Pulled the truck off the trailer and noticed the fuel pressure was low.
So I changed the fuel filter since I had an extra one. Upon starting the truck the fuel pressure went up to about 38 psi then droped down to 26 psi.......
Any ideas guys????? I am lost as to what could be going on.....
I did some searching and I don't think one pump is out, because the truck still runs??? could it be sumthing NOT related to the fuel system?????

thanks for the help!!

 

Think your gauge is right? Did you run it or just idle? With one pump i would think is can idle fine. Line loose at the tank maybe? kinked? Fuel cutout relay ?

Hmmm....

 

When I upgraded to the big injectors / pumps I had to bypass the relay that controls the power to the pumps and just run the pumps at 12v constantly (As opposed to a stepped down voltage at idle / part throttle...)

If you look in your manual, it shows where the relay is, just build a little jumper with male-spades on each end and take the relay out..

If I get time I'll go out during lunch and snap a pic of my jumper..

Its worth a try...

-Dale

 

The relay shuts it down with to much pressure right? thinking its a problem?

 

It drove fine... it never died or anything. From my search I read sumwhere that if the line came off the pump the trucks FP would be about 18 and it would not run much past idleing.... mine drove around the pits and everything......

 

Is there another way to test fuel pressure without using a guage????

EDIT: I mean like a fuel pressure tester or something???

 

ICU - The relay actually lowers the voltage to the pumps at anything less than just part throttle (2.3v at the TPS or something)

Thats the same thing mine did... Until I bypassed the relay..

Certain 255 pumps dont like operating at a voltage lower than 12 so when the relay is in and you are idling / part throttle it runs like a$$ cause the pumps cant make pressure.. then when you got WOT the relay gives the pumps full voltage and it builds pressure.. Thats how I figured mine out.. I could rev the motor and at a certain point it would build up a bunch of pressure..

-Dale

 

Hmmmmm... I think what you have done to yours is what my buddy showed me with a wire........ and my fuel pressure shot up to about 50 psi or so........

But if they dont like being run at low voltage..... how come they are just Starting to do this now????



EDIT: BTW thanks for all the help guys!!!!!!

 

Anyone else?????

 

Mine did the exact same thing...

Do you have an adjustable regulator? If so, the reason it jumped up so high is 'cause you probably had the regulator adjusted to give you good pressure at idle, but the pumps werent pumping like they should... so when you put full power to the pumps, the regulator is mis-adjusted...

Thats what happened with mine, at least...

-Dale

 

hmmm no adjustable regulator....... GGGRRR
I think i am gonna go..

 

Mine idles about 30-31 pounds.

If you installed larger injectors couldn"t they possibly lower the differential pressure? If the pulse width and duration are larger and or longer maybe they do create a pressure drop at the pump.

 

My FP is 36 at idle & 58 at WOT,i have the 255's & 50# injectors.
I had 1 of the Original fuel lines in the tank crack & i had 19 #'s of FP.

 

Would someone please post a picture of the jumper wire connection. I am not sure which two prongs to jump. There are 5 prongs on the relay.

 

Here ya go:



-Dale