Engine/Transmission (1998.5 - 2002) Fuel Pressure readings climb when underhood temps rise

[PRout]

So what do you suspect is the culprit??

I have a 3/8" x 2' run of SS braided hose tee'd off the VP44 to the FP isolator, and from there it sends antifreeze into the cab that connects to the Isspro EV mechanial gauge. Pretty standard right??

Readings are fine until I hit the desert, or on hot days when the underhood temps rise, then the gauge starts gradually rising from the 13. 5 norm, up to 20 sometimes. . Last weekend it actually climbed and pegged the gauge at 30!! It also stays around 8psi after shutting the truck down, and creeps down to 0 after awhile. .

For history. . Ive changed the gauge itself, have all new fuel lines, new upgraded fass motor, block, return spring and ball. This has been happenng for about 5 yrs, and after changing everything but the ss hose, and isolator the problem continues. . Also verified normal pressure at the fass by installing a temp gauge there. . It doesnt move off 14 psi.

Guess its either a heat sensitive isolator, or air on the supply to it, or in the antifreeze line. . Just wondering if anyone knows from thier experience. .


Tia for helping with this pia.

 

[mhenon]

Mine does something just like that. On cold mornings it's down to 13-17psi. When it warms up or on hot days it will go right to 24psi at idle.

I bled the line to the isolator and it stayed solid at the +20 figure for about a week. Now it's acting funny again. I'm not sure at this point what the "real" psi is.

Probably need to get a mechanical gauge and just hook it up real quick to see what pressure I'm running.

Mike

 

[PRout]

Exactly. . Need a mechanical gauge without an isolator in line to see what the pressure really is. Im definitely suspecting the isolator has air in it and when it heats up its showing expanded air in the lines. . Also. I have watched the pressure rise on the gauge after shutting the motor off. It will drop down to 3 psi, and gradually start climbing. Im pretty sure its getting heat soaked under the hood and expanding air in the line to the isolator. . Thanks for the reply.