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Therealarw · 06-29-2023, **(Subject: Fuel Problem Cummins )**

Hello everyone,
I've been having this problem that I haven't been able to figure out for over a week now. I have a 2014 Pete with a Cummins ISX15 CM2350. When I go to cycle the key switch on to turn on the electric lift pump, I notice that the fuel filter on the outside of the frame will syphon down to about the bottom of the fuel filter, rather than staying up and full. The truck will run still but then it'll eventually shut off at idle. What I noticed is that when the lift pump is going for the 60 seconds and I open up one of the fuel tank caps I can see the fuel going out the return pipe on the bottom. I've replaced the high pressure relief valve on the end of the fuel rail. It's still doing the same thing. I'm completely stuck on this. Is there anyone who has dealt with this same thing that could steer me in the right direction? Thank you!

Therealarw · 06-29-2023, **(Subject: Fuel Problem Cummins )**

Also to add on, it’s super hard to start, takes a couple key switches to get it to start, shuts off at idle, any help would be very appreciated. Thank you

Rawze · 06-29-2023, **(Subject: Fuel Problem Cummins )**

maybe sucking air at the top of one of the fuel tanks due to a cracked pick-up tube?.. just a random thought.

Also,.. will it pass a rail leak test exactly according to this video???...
http://rawze.com/forums/showthread.php?t...3#pid75483

Therealarw · 06-30-2023, **(Subject: Fuel Problem Cummins )**

Hi Rawze,
Yeah I thought it was that also. I'm definitely going to do a fuel injector leak down test as soon as I get it back to operating order. Unfortunately, the high pressure fuel pump took a sh*t and had gotten metal shavings throughout the oil system. Currently got the main bearings out. Crank is going to need a a quick polish on some of the mains. But I think the fuel is bypassing somewhere maybe the injectors? I noticed on all the other Petes when I go to cycle the key and the pump is running I don't see fuel flowing through the return pipe. It's just on this truck I have in my shop; also when I pull of the return lines off the fuel tank from the truck a lot of fuel will come out and the truck isn't even running. I'm going to invest in some compucheck gauges so I can see really see what's going on. It's been a hell of a job. Trucks been putting me back 2 weeks. Going to try what you sent me once I get it running. Thank you again

Therealarw · 06-30-2023, **(Subject: Fuel Problem Cummins )**

(06-29-2023 )Rawze Wrote: maybe sucking air at the top of one of the fueol tanks due to a cracked pick-up tube?.. just a random thought.

Also,.. will it pass a rail leak test exactly according to this video???...
http://rawze.com/forums/showthread.php?t...3#pid75483

I tried a different fuel tank off a wrecked truck I have and it seemed to still do the same, I'll keep you updated as soon as I find out what it could be

Rawze · 06-30-2023, **(Subject: Fuel Problem Cummins )**

You did not mention what type of external fuel filter. Is it a Davco?.

Does it have a 10-micron filter element in it?.

It is dropping BELOW the filter element?... or just dropping near the bottom of it?. it should not drop below the paper element.

Anyone checked to ensure the bowl of the fuel filter housing itself is not leaky?.

One way to check for pick-up line and tank leaks is to pressurize the fuel tanks to 10 psi shop air onto the bleeder tubes, and let it sit for an hour or so. Check if fuel is seeping out somewhere. WHATEVER YOU DO THOUGH!!! if you pressurize the fuel tanks for a test ... NEVER OPEN THE FUEL CAPS WHILE THE TANK IS PRESSURIZED!!!! .. NOT EVEN A FEW PSI!!! .. BECAUSE THEY CAN AND WILL BREAK YOUR HAND OR ARM!!! put a person in the hospital real fast. There is a LOT of force behind those fuel caps even with only a very few psi pressure in the fuel tanks.

Therealarw · 07-01-2023, **(Subject: Fuel Problem Cummins )**

(06-30-2023 )Rawze Wrote: You did not mention what type of external fuel filter. Is it a Davco?.

Does it have a 10-micron filter element in it?.

It is dropping BELOW the filter element?... or just dropping near the bottom of it?. it should not drop below the paper element.

Anyone checked to ensure the bowl of the fuel filter housing itself is not leaky?.

One way to check for pick-up line and tank leaks is to pressurize the fuel tanks to 10 psi shop air onto the bleeder tubes, and let it sit for an hour or so. Check if fuel is seeping out somewhere. WHATEVER YOU DO THOUGH!!! if you pressurize the fuel tanks for a test ... NEVER OPEN THE FUEL CAPS WHILE THE TANK IS PRESSURIZED!!!! .. NOT EVEN A FEW PSI!!! .. BECAUSE THEY CAN AND WILL BREAK YOUR HAND OR ARM!!! put a person in the hospital real fast. There is a LOT of force behind those fuel caps even with only a very few psi pressure in the fuel tanks.

Rawze,
It’s actually a Paccar Filter it’s a K37-1004. Which I think is a 10 micron. But the fuel stays about at the bottom of the fuel filter. It’s the only truck in my fleet (20 trucks) where the fuel is at the bottom of the filter. This is with the truck not even running. I’m thinking I have a few leaking injectors because it’s a hard start. Takes 3-4 key cycles just to get it to run and it runs super rough for 5 seconds before idling the right way. Then I noticed the truck will shut off when RPM’s drop down to idle, then I have to cycle the key again to get it running. Unfortunately I can’t test it out right now as I had to drop the main bearings. Most of them had been scarred due to the fuel pump failing

The bowl is fine, it’s pretty new, all the suction lines have been replaced.

JimT · 07-09-2023, **(Subject: Fuel Problem Cummins )**

Not sure how long this has been going on or when the pump died, but did you consider that the failing pump could have been the cause of the issue?

Conversely if you're getting air into the system ANYWHERE before the high pressure fuel pump that could have been the main contributing factor to the fuel pump failure. The plungers in the pump head rely on the fuel for lubrication and any air infiltration could lead to increased friction. While it probably can withstand the occasional air bubble repeatedly running out of fuel will most likely accelerate wear along the plungers. This is my own speculation here, but I wouldn't be surprised if this is the underlying root cause of these pumps dying, especially with the old ceramic plungers as opposed to the steel ones.

I mention both these specifically because you said it takes 3-4 key cycles to get it started then runs rough. This implies that the issue is on the priming side. If it was on the high pressure side it would simply take extended cranking as opposed to key cycles (priming). It could be sucking air anywhere between the high pressure pump and the tanks.

Therealarw · 07-10-2023, **(Subject: Fuel Problem Cummins )**

(07-09-2023 )JimT Wrote: Not sure how long this has been going on or when the pump died, but did you consider that the failing pump could have been the cause of the issue?

Conversely if you're getting air into the system ANYWHERE before the high pressure fuel pump that could have been the main contributing factor to the fuel pump failure. The plungers in the pump head rely on the fuel for lubrication and any air infiltration could lead to increased friction. While it probably can withstand the occasional air bubble repeatedly running out of fuel will most likely accelerate wear along the plungers. This is my own speculation here, but I wouldn't be surprised if this is the underlying root cause of these pumps dying, especially with the old ceramic plungers as opposed to the steel ones.

I mention both these specifically because you said it takes 3-4 key cycles to get it started then runs rough. This implies that the issue is on the priming side. If it was on the high pressure side it would simply take extended cranking as opposed to key cycles (priming). It could be sucking air anywhere between the high pressure pump and the tanks.

Hi JimT,

So yes I actually do have to continuously crank the motor over to get it to run, it runs super rough, like it almost sounds like it’s running off a few injectors, it’s super hard start and then once you get it to run it idles super rough.
Also I see the fuel bowl on the outside filter go down all the way as if it’s returning the fuel faster than the pump can keep up with it if that makes sense. When I look at another truck I noticed that when you turn the key for the electric lift pump the fuel won’t start returning through the return side until the motor is actually running.
On this truck I’m diagnosing, when I cycle the key on for the lift pump when I go to take the fuel cap off the fuel tank you can see the fuel going through the return line of the tank as if it’s bypassing. So to me it seems like it’s not holding its prime when you go to cycle the key and the lift pump starts priming the fuel pump.