Hello all, I'm new to the forum. My older Lull telehandler has recently started acting up intermittently. The Cummins 4 cylinder has been starting to run really rough after the machine gets up to temp. If I shut it down and let it sit for even 5 minutes, it will sometimes run better for 5-10 min. I drained fuel, refilled with new fuel (no water to speak of and old fuel seemed fine) then replaced inline and main fuel filters. After doing this it ran much better for a few hours, then went back to the same behavior. Please advise me on what to check next. There was not a bunch of junk in the tank such that I might expect a fuel filter to get clogged up that fast, I thoroughly cleaned the sludge of age out of the tank when I bought it two years ago. This feels like something minor that I jut need to isolate. Thank you!
Look at the lift pump there might be a screen on theinlet side of it if I remember. What it the serial number of the engine ?
Will check the lift pump for a screen next time I’m out there. Unfortunately it’s at a remote jobsite. Will get the engine serial next time I’m out there too. Machine serial is 18038.
Some of those lift pumps have a reputation for early death, you could test the running pressure, or just replace the lift pump.
Can a lift pump go out gradually, causing poor running? Seems like the sort of thing that works or doesn’t work?
What kind of pressure should I be looking for?
Above zero. Probably real close to the same pressure cold as hot. A pressure/vacuum gauge will give you enough range. You can look up a spec based on the injection pump. Cummins used at least a couple different injection pump styles. If that doesn't show a problem, post a pic of the injection pump and id tag for thepumpguy.
If it sounds like it's only running on 3 cylinders it could simply be a faulty injector. If it's an older B series Cummins they're pretty easy to crack the nut at the injectors and find which one remains dead when you crack the line nut.