DoctorCheney223

Hi Folks,

Here is the situation:

Outside temp is 97 degrees. Vehicle does have fuel as I added 2 more gallons just to make sure it wasn't a stuck gauge. This is a 1986 M998 with a 6.2L that ran perfectly yesterday. There are three other occasions when trying to start the vehicle it took approximately 15-20 seconds of cranking the engine before it would start. There is white smoke coming out of the exhaust pipe while the engine is cranking.

I don't know where the fuel filters are located on this vehicle so I can't check for clogged filters and I haven't yet pulled a fuel line to verify if the fuel pump is working properly.

Any ideas of what this might be before I have to pull a fuel line and check?

thanks,
Ron

1967 M109A3
1986 M998 HMMVV
1988 M35A2C
1974 M35A2
1970 M35A2
1971 M35A2
1971 M35A2
19XX M35Z2

Chief_919

White smoke coming out when you crank? That means it is getting at least some fuel. My first check would be the glow plugs.

DoctorCheney223

Any way to determine if the glow plugs are not functioning correctly? This is my first diesel and have no clue but I will start doing some research ASAP.

thanks,
Ron

1967 M109A3
1986 M998 HMMVV
1988 M35A2C
1974 M35A2
1970 M35A2
1971 M35A2
1971 M35A2
19XX M35Z2

kipman

Does the glow plug selonoid make a thunk sound?

ida34

Check for power at the glow plug terminal with a volt meter or test light. It should light while the wait light is on then they should stay on for a short time after the wait light goes off. If you are getting power to the plugs then check the individual plus by connecting a test light to positive power then touching the terminals on each glow plug with the connector off. This can be with the ignition switch off. If a glow plug does not light the test light it is shorted internally and is bad. I would bet you have a few plugs failed.

Chuck Graham
1969 Kaiser-Jeep M35A2

kipman

Chuck, you post was better than mine.

DoctorCheney223

When I move the lever from STOP to RUN, I do hear a thunk sound. Is that the sound you are talking about or is there another one that I should be listening for?

Also, the "wait" light goes on and off instantly and doesn't have ANY type of waiting period.

thanks,
Ron

1967 M109A3
1986 M998 HMMVV
1988 M35A2C
1974 M35A2
1970 M35A2
1971 M35A2
1971 M35A2
19XX M35Z2

Chief_919

There is your problem- your glow plug system has an issue. Now we need to know if you have an old system or a new system.

On the firewall, drivers side, is a protective control box, a black box with cannon plugs where the wiring goes in.

Give me the NSN on it and we can go from there in troubleshooting. If it is an old one, I will bet your glow plug controller is bad. But there is one that has a temp sensor where the glow plug controller went, and others that don't use the controller or temp sensor so I need to know what one you have.

Also, before we do much more, verifiy you have a good ground to the frame from the engine and from the PCB. Grounding issues sometimes cause this.

Hell On Wheels

If the volts check out, food for thought, check the injector pump lining marks on the center top front of the pump, where it mounts to the housing. The lines should be aligned. Sometimes mechanics do not tighten these mounting bolts to the right torque and these bolts will get loose. I have had a few in my life time. Just to ensure and eliminate this troubleshooting procedure.

Check the fuel water separator as well, located in front of the washer reservoir. Get a cup and turn the engine for approximately 15sec to see if you get bubbles out of this, if so you have water in the fuel.

If you replace the controller insure you wait about ten minutes for it to adjust to the temp. I would change out controller and glow plugs at the same time. Bad controllers stems from not waiting for the wait to go out before starting. This problem could have been the previous owner’s bad habit.

DoctorCheney223

Here is the info located on the cover of the PCB.

NSN: 6110-01-395-9585

Manufacture: Prestolite Electronics, Inc.

1967 M109A3
1986 M998 HMMVV
1988 M35A2C
1974 M35A2
1970 M35A2
1971 M35A2
1971 M35A2
19XX M35Z2