Low fuel pressure - Dodge Cummins Diesel Forum
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post #1 of 74 (permalink) Old 04-18-2019, 06:29 PM Thread Starter
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Low fuel pressure

Hello,

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.

The ride:

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.

The issue:

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!

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post #2 of 74 (permalink) Old 04-18-2019, 06:37 PM
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Did you try new fuel filter and the gas can under hood at the same time and still no change? How much fuel is coming out of the return line?
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post #3 of 74 (permalink) Old 04-18-2019, 06:39 PM
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Also how is the mechanical gauge hooked up? If you have a hose going into the cab maybe itís kinked? Another idea is if you have a snubber valve in the line (you should) maybe itís plugged?
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post #4 of 74 (permalink) Old 04-18-2019, 07:12 PM
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Have you checked the pickup screen on the fuel tank module?

What kind of a LP are you using?

Is your fuel pressure gauge after the filter?

84 K5 Blazer 97 12v, 47re with E-TransControl, Dodge Dana 60 with free spin hubs, Dana 70, B&M Mega shifter

96 F350 SC dually zf5, 4x4, 92 Cummins, THD 5x12's, THD fuel pin, THD HVLP with adjustable fuel pressure mod, WM, h1c 60/60/12cm WG wired
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post #5 of 74 (permalink) Old 04-18-2019, 07:25 PM Thread Starter
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Quote:
Originally Posted by myother4x4isaCJ7 View Post
Did you try new fuel filter and the gas can under hood at the same time and still no change? How much fuel is coming out of the return line?

Yes the new fuel filter was on when the gas can was hooked up under the hood. I'm not really sure how much is coming out of the return line but when I had the gas can hooked up to the lift pump the disconnected fuel line from the tank had a steady flow of diesel coming out of it while the engine was running and after I shut the engine off until I removed the fuel cap.
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post #6 of 74 (permalink) Old 04-18-2019, 07:35 PM Thread Starter
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Quote:
Originally Posted by myother4x4isaCJ7 View Post
Also how is the mechanical gauge hooked up? If you have a hose going into the cab maybe it’s kinked? Another idea is if you have a snubber valve in the line (you should) maybe it’s plugged?
The mechanical has the banjo bolt from geno's replacing the original bleeder screw with a brass fitting to a needle valve with a rubber hose going through the firewall to the dash, diesel fuel in the line. There are no kinks & I've bled the line quite a few times using the manual lever on the lift pump. Don't have a snubber.

Btw, I like those CJ-7's

Thanks!
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post #7 of 74 (permalink) Old 04-18-2019, 07:50 PM
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In the original post you referred to a needle valve in the gauge line, that is a snubber.
Have you tried running it with the valve wide open and/or check for junk in the valve.

Had you done any work to the truck before this started?
What type of fuel hoses do you have before the lift pump? Maybe sucking flat when it warms up and that leads back to a restriction in the tank pickup and supply line.

Cheers Steve

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post #8 of 74 (permalink) Old 04-18-2019, 08:11 PM Thread Starter
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Quote:
Originally Posted by 9297oldram View Post
Have you checked the pickup screen on the fuel tank module?

What kind of a LP are you using?

Is your fuel pressure gauge after the filter?
Last summer I dropped the tank and inspected, everything in there appeared to be fine.

I would assume after using the gas can under the hood, bypassing the fuel line back to the tank, still having the same symptoms would rule out any issues back there.

I'm using a stock lift pump mounted to the engine block, genuine cummins.

Fuel pressure gauge is after the filter
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post #9 of 74 (permalink) Old 04-18-2019, 08:19 PM
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Have you tried dumping cold water on the IP when your fuel pressure drops?

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post #10 of 74 (permalink) Old 04-18-2019, 08:30 PM Thread Starter
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Quote:
Originally Posted by Blackduck59 View Post
In the original post you referred to a needle valve in the gauge line, that is a snubber.
Have you tried running it with the valve wide open and/or check for junk in the valve.

Had you done any work to the truck before this started?
What type of fuel hoses do you have before the lift pump? Maybe sucking flat when it warms up and that leads back to a restriction in the tank pickup and supply line.

Cheers Steve
Steve,

Cool I guess I do have a snubber then,

I'll try it tomorrow with the valve wide open. Good idea.

No work was done to the truck before this started, all factory lines back to the tank.

Thanks!
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post #11 of 74 (permalink) Old 04-18-2019, 08:33 PM
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Quote:
Originally Posted by Crazymonkey View Post
Steve,

Cool I guess I do have a snubber then,

I'll try it tomorrow with the valve wide open. Good idea.

No work was done to the truck before this started, all factory lines back to the tank.

Thanks!
I doubt if the snubber or needle valve is the issue because you say the engine wants to die when the pressure drops.

Also when you had the jug connected did you use a different fuel line from the jug to the LP?

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post #12 of 74 (permalink) Old 04-19-2019, 08:48 AM Thread Starter
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Quote:
Originally Posted by Blackduck59 View Post
In the original post you referred to a needle valve in the gauge line, that is a snubber.
Have you tried running it with the valve wide open and/or check for junk in the valve.

Had you done any work to the truck before this started?
What type of fuel hoses do you have before the lift pump? Maybe sucking flat when it warms up and that leads back to a restriction in the tank pickup and supply line.

Cheers Steve
This morning outside temp is 54.5 degrees F. Started the truck and fuel pressure is showing 4.9 psi. I opened up the needle valve all the way with no fluctuation showing on the gauge.

thanks for the suggestion!
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