Engine/Transmission (1998.5 - 2002) fuel pressure vs amount of fuel in tank

[wcoomes]

I took about a 160 mile trip yesterday and noticed something. My fuel gauge no longer works so I fill up when the trip odometer hits 350 miles to be safe. However, I noticed that the emptier my tank gets, the less fuel pressure I have. I started out yesterday's trip at 10-12 cruising at 70 on the interstate. Later it dropped to 8-9, then 4-5. I stopped and got 7. 5 gallons as the price was a bit high to fill ($2. 55/gal) and drove back to Flying J with fuel pressure at 5-7 all of the way. After filling up, fuel pressure at 15 @ idle, and back to 10-12 cruising at 70! What is going on??

 

[JCyrbok]

Mine has done the same since new. I chaulk it up to less fuel creating less "head" pressure to assist. Also the level goes down the pump has to pull the fuel farther up the pick up tube, which I think moves up and down with the tank module as the tank is emptied.



I see maybe 1/2-1psi difference at idle, but a couple of Psi at WOT difference, when the tank is down around 1/4tank.



Hope this helps



J-

 

[jerrethomas]

Same thing with my truck as said above.

 

[RSimmons]

I suspect that fuel temperature has a big part in this also. The longer you drive and the less volume in the tank, the warmer the fuel will be.

 

[DMannon]

Do you get a whooshing sound when you open the gas cap? You might try looking at the top of your fuel tank pickup and see if the liitle cap was left on the vent from the factory...