Engine/Transmission (1998.5 - 2002) Safe Fuel pressure for VP44?

[Doughboy21kd]

I put a new lift pump on and can control my fuel pressure with a turn of a screw... . Right after install i started up to fine tune it and it was pre-set at 25psi... i turned it down to about 19-20psi at idle... Yesterday while driving i noticed a abnormal idle like it was fluctuating up and down, kinda like it was cavitating sorta... .



So i was reading(learning) the forums and started reading about the APPS adjustment, thinking maybe it was that... . Then i started reading about some of the safe limit fuel pressures for the VP and it seems that, at idle most are stating that keeping it between 13 and 15 psi at idle is best. So i went outside and lowered the fuel pressure to about 13. 5-14 at idle and it seems that my abnormal idle has maybe dis-appeared.



Whats you take on this? You think that 20psi may have been too much for the VP to handle and it was causing it to idle up and down like that?



I watched my volt meter and the grid heater was not cycling. And there was no load being put on the motor. I do know though that when my fuel pressure was set at 20 and it was in "D" or "R" where the transmission was engaged that my idle was just fine... It seemed to only do it at idle with NO load on the motor... .



I'll drive it more tommorrow and see what it does but i just thought i would ask for some opinions... THANKS

 

[Mundgyver]

The VP 44 has a 14psi inlet bypass that returns fuel to the tank and also vents any air out of the pump inlet through a very small orifice just below the bypass ball and spring. You are looking to set your pressure to 15 psi. Too much pressure and you can damage the VP which is just as bad as too little pressure.



What I did when I installed my FASS system was to increase my fuel line from the tank to 3/8th ID line all the way into the VP with a straight in fitting. I got rid of the banjo fittings. My pressure is set at 15 psi at idle. The 3/8th ID allows me to increase my volume of flow to the VP but not over pressure it.



The VP can take all the fuel it wants without my worrying about having to keep my pressure up.



I have been running this way for about 180,000 turns now and the truck has 208,000 on it and I am still running the factory original VP.