Engine/Transmission (1998.5 - 2002) FASS system and fuel pressure

[dknoch]

I have a FASS system on my 02 for about a year now. My fuel pressure on a westach guage (about 1. 5 years old) used to be about 16 at idle and 12 at wide open. It seems now that on really hot days 85+, my fuel pressure will be about 13 idle and 10 wide open. The cooler days it will be about 14-15 at idle and 10-11 at wide open. Where should I look first? Could it be the fuel pressure sensor is wearing out or possibly the spring in the FASS that controls pressure is weakening? I am looking for advise. Thanks for your help.



Dan.

 

[Greenleaf]

My Westach will drop in pressure on very hot days. About 2 psi less. Has always done this.



GL

 

[DCutler]

On my fass 150 i have 21 at idle 18-19 cruise 16 @wot I dont have the westach gauges but It does vary a little on the hotter days I have the digital edge gauges, hope this helps, is your filter f/fuel clean?

 

[JCyrbok]

My SPA gauge has always done the same too, whether with the FASS or stock pump.



My thoughts are that just like motor oil, diesel will lose some viscosity as it gets hotter or is "heated" by the atmosphere. Just like your engine oil pressure is lower when hot at idle, then when u first fire up truck in the morning.



In addition, with the FASS, I would rationalize that hotter fuel puts off more vapors, as would a half of a tank, alot of aggitation, etc. The FASS removes the vapor/air in the fuel and returns it to the tank through the return. More vapor=more vapor (along with fuel) removed from the supply to the VP/FP pick up=lower pressure?? Sounds good atleast.



Anyone one else think that this sounds likely, or just me?LOL



Hope this helps,

J-