Can the 8.3 run with bad lift pump?

[daschae]

M923A2 I just picked up will run with vigorous pumping of the transfer pump and ether while cranking. Will stay running no problem for as long as I want, even idle. If I shut it off and immediately try to restart it, it will crank and not fire at all, not even a little, same is true if I wait overnight. Fuel lines from tank to pump are good, new rubber. I sucked fuel up to the inline filter, and pinched the line with vice grips, waited a few minutes, then released them and fuel was still in the line, I could hear it running back into the tank, so Im confident the leak isnt between the tank and pump.

So here is whats confusing me, can the cummins run if you get it going with a bad lift pump? Does the IP create suction that would keep pulling fuel from the tank?

Also, even when I am pumping the **** out of the primer, it doesnt create hardly any (if any) suction. I put my finger over the fuel supply inlet and it doesnt even suck enough to pull my skin.

Any thoughts on this?

 

[WillWagner]

They usually will not start w/o a working lift pump, the fuel pump needs a minimum low pressure to make the high pressure for it to start and run. The biggest issue is the overflow valve. ( http://www.steelsoldiers.com/showthread.php?140259-M939A2-Adjustable-return-fuel-check-valve ), there is a good pic of it in that thread.

 

[daschae]

Ordered the Torktek adjustable, will report back if it fixes problem.

 

[Csm Davis]

Do you have an all plastic lift pump or the metal one if it's the plastic one I would recommend getting the metal one and also did you replace the the rubber fuel lines or are you just saying they look good? I have never trusted any rubber fuel line on a MV they can look brand new and be crap. I would pressurize the line from the tank forward to the hard lines on the secondary filter and see if there are any leaks. If not then look at the valve mentioned above.

 

[maccus]

The return fuel check valve should fix it I would think. Your problem is very similar to my problem and the check valve did the trick. I had replaced the transfer pump with a new one earlier. Were it me I would replace the transfer pump anyway as they are a mechanical unit and they get tired after a while. Also the transfer pump has a check valve in it That way you would have replaced both check valves in the fuel supply/return path.

I bet Will (Cummins person) can come up with the latest part number (version) of the lift pump. As there have been a few pump part numbers used over the years.

 

[daschae]

Fixed!

Clamped the return line, still wouldnt restart. Replaced the transfer pump, works perfect! Here is the test for the transfer pump, if after priming the truck you cant get it to make the swish swish noise at the injector pump, the transfer pump isnt moving enough diesel.



Now on to truck number 2 that loses its prime after 24 hours.