Engine/Transmission (1998.5 - 2002) Lift Pump - Cold Weather pressure

[socal_rattler]

Recently it has been getting down into the 30s at night here and I have noticed that when I start in the morning, I only get about 5PSI fuel pressure until the engine gets warmed up some, then it goes up to anywhere from 10 to 13PSI.



I don't know if this is normal or not since it doesn't get that cold here is SoCal very often. I recently changed the fuel filter and did not notice this until after I changed the fuel filter, but frankly, I wasn't watching the fuel pressure too often prior to changing the filter when it had been cold.



If I start it up in the afternoon when the weather has warmed up some, it goes right up to between 10 to 13 PSI.



So at this point, I don't know if it is a filter issue, a lift pump issue, or no issue.



I know... I know... I need to get an Airdog or something similar and hope to do so soon, but I wanted to get some input on this.



Thanks.

 

[Gary - K7GLD]

Two words:



GRID HEATERS!



In colder weather, the intake grid heaters will cycle, dropping electrical system voltage - and the LP PSI will fluctuate also, until the intake temp rises above it's limit and grid heater cycling stops...

 

[socal_rattler]

Thanks Gary, I did not think of that. So should I just idle till the grids get things heated up? I am still concerned that not enough fuel is getting to VP44 with only 5lbs of pressure.



Do you know if this same issue would occur with an Airdog since the voltage will still be fluxing?

 

[Gary - K7GLD]

Thanks Gary, I did not think of that. So should I just idle till the grids get things heated up? I am still concerned that not enough fuel is getting to VP44 with only 5lbs of pressure.



Do you know if this same issue would occur with an Airdog since the voltage will still be fluxing?

I suppose some motors as used to power fuel pumps will be more sensitive than others - but generally, they probably all will display at least SOME loss of performance while the grid heaters are cycling. As far as taking it easy while the engine reaches operating temperature, probably no more than you would with a cold engine anyway - at least I tend to baby mine until it warms up.

 

[WestTN]

The fuel is also more viscous when cold. This is precisely why the fuel heater is on the truck.

 

[mhenon]

You might also check for air in the fuel gauge line. Mine did this exact thing and drove me nuts 'till I fugured it out. In my system it was the clear line from the isolator to the gauge that was leaking.

Mike

 

[Schlickenmeyer]

Well, as I have a very similar rig, and live in a colder climate, here be my 2 cents.

I have been tracking my pressures for a while now, and I lose around 2 psi when

it gets single digits. I normally see a max of 12. 6psi. This was with the old pump and the new one I put in about 10k ago. Your fluctuation seems pretty wide. I would check for the air bubbles as listed above, and check to see if the fuel heater built into the filter housing is working. Also verify your gauge if you have the ability, Could be a sender if you have an electronic gauge.



Good luck.