Starting and Running problems with NH L255

[welby]

I'm working with my neighbor on the subject Skid Steer and have encountered 2 problems, maybe related or not. 1st a little background, this model is a small Skid Steer with a 3 cylinder diesel and this one has about 1500 hours on the clock. Currently if you try to start the engine in normal Operate mode it will crank until the engine starts to catch then the starter drops out before it will start. Typically the seatbelt lights pops on about then as well. If you try to start it in Service mode it will start and run fine. You can then switch to Operate mode until the next problem crops up. By the way, nothing appears to be wrong with the seatbelt switch. The 2nd problem comes into play after you have been running for about 5 minutes+- in Operate mode. The engine just dies dead, no sputter, no nothing. I assume this can only mean that the fuel solenoid has closed since that is the only way to shut off a diesel that abruptly. If you start the machine in Service mode you can drive it around indefinitely and not have it die. This I find quite unusual because the fuel solenoid it is not tied to the safety system in any way yet it works differently in Service mode than it does in Operate mode. The schematic shows the power for the Fuel solenoid coming off the main switch "ignition" position, through a diode and to the fuel solenoid. The wiring harness seems to bare this out so it's difficult to see where the interruption is. Any thoughts would be appreciated.

 

[Tazza]

The running then it stops sounds like its detecting a fault somewhere. This is usually a failsafe if it detects low oil pressure, low coolant etc. Just to help save the machine from damage. Charger is the man for NH machines, Ken may have a few ideas of where to start too.

 

[welby]

The running then it stops sounds like its detecting a fault somewhere. This is usually a failsafe if it detects low oil pressure, low coolant etc. Just to help save the machine from damage. Charger is the man for NH machines, Ken may have a few ideas of where to start too.

Taza, Thanks for the feedback. There are only 3 engine sensors on this machine. There is a water temperature switch which is tied to the water temperature light on the display. There is an oil pressure switch which is tied to the oil pressure light on the display. There is a engine temperature sensor that is tied into the glow plug controller, presumably to adjust the time the glow plugs are activated. The 2 sensors that are tied to the indicator lights are not activating the lights when this quiting problem occurs so I'm guessing this is not the problem, plus the documentation does not show them tied to any other circuit.

 

[skidsteer.ca]

Taza, Thanks for the feedback. There are only 3 engine sensors on this machine. There is a water temperature switch which is tied to the water temperature light on the display. There is an oil pressure switch which is tied to the oil pressure light on the display. There is a engine temperature sensor that is tied into the glow plug controller, presumably to adjust the time the glow plugs are activated. The 2 sensors that are tied to the indicator lights are not activating the lights when this quiting problem occurs so I'm guessing this is not the problem, plus the documentation does not show them tied to any other circuit.

Try hooking a temporary test lite to the fuel solinoid circuit to confirm your hunch that the power is being lost there. Sounds like a loose conection, bad relay etc, that the service mode switch somehow bypasses.
Ken