Engine/Transmission (1998.5 - 2002) Is it normal for fuel pressure to be lower on cold mornings?

[Rattlin_Ram]

Mine is anywhere from 1-2 lbs lower at idle than normal. Normally I get between 14-15psi at idle and cruise at 11-12 or so, and WOT is around 9. I don't usually do WOT on the cold engine, so I'm not sure what my lowest number is there, but cruise when cold is around 10-11. After the temps come back up on the engine, all seems good again. Just wondering if this is normal, or if I may have an isolator problem or something. I think my LP I put in 2 months ago is still good. Oh and the cold morning temps have been around 30deg or lower outdoor temp, and I let the truck warm up for about 5 min or so before I leave for work.

 

[PHellums]

I think it's normal? I've got an '01 setup about the same as yours and I get those exact readings first thing in the mornings or after it's been sittin' all day at work.

 

[mhenon]

That's what my guage is doing. Cold mornings and cold fuel. . the pressure is down a little. Once the fuel warms up, the pressure does too.

Mike

 

[WestTN]

Fuel viscosity is higher when cold, so the pressure drop across the filter is higher.

 

[Todd T]

also when the grid heaters are running it will brown out the lift pump a bit and drop pressure that way.