When the machine is running it will randomly start sputtering and sometimes die. We are thinking it might be the fuel pump but anyone have any idea where to start? We are also having issues with the lock handle not unlocking the controls. Anyone had problems with this?
Install fuel pressure gauge and monitor while working
Does it start right back up or do you have to crank it a lot? Also are the fuel filters empty after it stalls? Does it stall all at once or does it sputter and slowly die?
Sometimes it stalls completely, sometimes it sputters and takes a while to come back. When you start it back up it cranks a few times before it fires. We have noticed it is worse when the tank is a lower.
What engine is it? Does it have a lift pump in the tank?
Here is what the spec sheet says on the engine. Isuzu A-4BG1T water cooled, 4-cycle, 4 cylinder in line, direct injection, turbocharged, and after-cooled diesel engine, 264 CID (4 329 cc), 4.13" (105 mm) bore x 4.92" (125 mm) stroke. No idea if it has a lift pump. Are those common on a 35k lb size machine?
A lift pump is common, I don't know about in the tank? Is there a tank drain that you can check for garbage? or can you get the pickup out of the tank easily to check if it's plugged/collapsed? If it has a "Zexel" inline injection pump you might have the lift pump as part of the injection pump, you can see by the fuel plumbing going to the injection pump then to the filter and back to the injection pump, also the priming pump is part of the transfer pump (small cylinder with 1" round cap that unscrews and pops up). That all sounds like plugging somewhere. or an air leak, any wet spots on fuel hoses?
All the hoses between the tank and pump have been replaced so they are in good shape and not leaking.
I guess that leaves the tank pickup and the pump then? Filter gaskets? You should see what you have for a lift pump, and like rmllarue said, add a fuel pressure gauge at the injection pump inlet and if that doesn't show a drop in fuel pressure when it's stalling then you have injection pump issues (or air). If the pressure does drop then look back to the tank. There might be a screen in a banjo fitting at the injection pump, worth a look.
there is a screen in the banjo fitting on the lift pump that could be plugged. if I remember right its the one on the bottom of the pump.
here is a pic of the lift pump
A lot of Isuzu applications have a plastic water separator housing before the lift pump and a screen in that banjo fitting going into the separator. I have seen that screen get plugged but also that water separator will crack or the oring that seals it will leak. You probably wont notice fuel leaking out because the separator is usually located pretty high in the machine in relationship to the fuel tank. More commonly air will leak into the fuel system causing your issue. Many times you can easily bypass the separator to see if it is your issue.