Join Date: Apr 2019
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Low fuel pressure
I'm new to the forum, and I've been scouring the internet for some help and cannot find anything similar to remedy my situation.
92 W250. 280k owned it for 5 years, had injection pump rebuilt, new stock lift pump & installed low pressure mechanical fuel gauge after fuel filter with a needle valve, last summer. Was running consistently around 7 psi.
This winter I noticed that when I would start my truck cold it would run at 7 psi, which is good from what I gather. As it warmed up the psi would gradually and slowly decrease all the way down to 0 psi after about 20-40 miles depending how cold it was outside. 15-35 degrees Fahrenheit. If I shut it down & started while engine was still warm it stayed at the same consistent low psi. After hours of sitting or overnight and the engine was cold once again it would start back up at 7 psi. I drove it all winter like this and just made short trips, not letting it get all the way to 0 psi.
Now that spring is here the ambient temp is in the 50's 60's & 70's
50 degree weather first start of the day I'm running @ 4psi and can only go about 15 miles before dropping to 0 psi
60 degree weather first start of the day 2-3 psi , not sure on distance, it was too low to drive anymore
70 degree weather 1st start .75-1psi
Haven't driven it for the past 2 weeks due to the warm weather, just starting it in my driveway troubleshooting.
What I've tried:
-Replaced fuel filter, old fuel filter looked fine with no contamination in the fuel
- new lift pump
- thought maybe I received a defective lift pump so ordered another. 2nd new lift pump still starting @ approx 1 psi
-assumed the grommet seals in the union between the fuel filter and ip were maybe worn out so ordered those from cummins and also replaced the seals on the same line at the outlet of the fuel filter
-swapped out my mechanical fuel pressure gauge for another. Getting same readings
-removed my fuel cap to release pressure in the tank
-rigged up a 1 gallon fuel can under the hood connected directly to the lift pump
- I read somewhere on the internet to block the return line, doing this didn't really do anything until I shut the engine off, then the gauge pegged @ 15 psi until I removed the plugged line that sprayed diesel all over.
I don't see any leaks, the engine runs great, starts at the touch of the starter, if I wasn't looking at the gauge I wouldn't know anything was even wrong
70 degree weather today running it is approx <1 psi, I notice when I turn the engine off the gauge jumps up to about 2-3 psi for a second or two then drops to 0
Not really sure what else to do, now with the weather being warm I can't drive anywhere
Any suggestions or ideas would be greatly appreciated
Thanks in advance!