# M9540 issue



## Dmullis37 (Sep 2, 2021)

I have an M9540 with 1300 hrs on it. It has been running fine for a year now but recently it will Run for a while and then start running rough and knocking and after about 30-45 seconds it will clear up and run fine again for a little while and then repeat. I have changed the fuel filter, cleaned out the water separator, and drained the tank and started with fresh fuel. It is still doing it. What do I check next?


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## SidecarFlip (Mar 25, 2021)

Starving for fuel. What year is it and is it common rail or conventional injection? More info needed. Last service and did you change the air filter at that time and is the filter minder in the red zone? Could be a number of things from a ill fitting fuel filter gasket to a collapsed fuel line to a faulty fuel hose letting air in the fuel system to a plugged fuel tank cap. Diesels need 3 things to run correctly, pressurized fuel, combustion air and compression to ignite the fuel.


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## Dmullis37 (Sep 2, 2021)

SidecarFlip said:


> Starving for fuel. What year is it and is it common rail or conventional injection? More info needed. Last service and did you change the air filter at that time and is the filter minder in the red zone? Could be a number of things from a ill fitting fuel filter gasket to a collapsed fuel line to a faulty fuel hose letting air in the fuel system to a plugged fuel tank cap. Diesels need 3 things to run correctly, pressurized fuel, combustion air and compression to ignite the fuel.


I did take the air filter out and blow it out just before it started happening. I ordered new ones and will install them today. It is a 2013 model. Not sure about the common rail or injection. I will check the lines today also. I am new to the Diesel engines. Thanks for the info!


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## SidecarFlip (Mar 25, 2021)

2013 could be either way, common rail (ECM Controlled) or conventional high pressure injection with a Bosch style injection pump It's important to know which it is because the fuel delivery systems are entirely different. I have basically the same engine you do, just a tad bit less power., but mine are both mechanically injected.

If you have a conventional injection pump, make sure the little handwheel knob on top of the pump is closed. If it's open at all, it will cause a rough idle.

Another overlooked source of air in the fuel is the plunger knob on top of the fuel filter. It needs to be screwed down when not priming.


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