Fuel Problem Cummins

[Therealarw]

(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.