M934A2 with 6CTA 8.3L Turbo Diesel will not run

[TexanOnTheMove]

I have a 1992 M934A2 5 Ton 6X6 expansible van with the 6CTA 8.3L Cummins Turbo diesel. When I bought the truck, it would fire up and run like a champ each and every time I would start it. Now all of a sudden, all it will do is turn over, but not stay running. I've already replaced the fuel pickup pump and tried bleeding it, but I can't seam to get it to pick up full from the tank. I can get it running for short periods on either, hoping it would prime itself, but it won't stay running. I've tried bleeding the system up to the fuel injector pump, but all it does is drain the fuel from the fuel filter and doesn't draw from the fuel pump. Any ideas on my next course of action?

Thanks,
TexanOnTheMove

 

[fuzzytoaster]

Make sure the fuel cutoff solenoid is fully retracting. Try zip tying it back or even removing it then give it a crank. If it's losing prime then try pressure bleeding the system and look for wet spots. More than half the A2s I've had in my hands had rotten rubber lines.

 

[wrenchturner6238]

You might also make sure there is no foreign material in the fuel tank going up the suction pipe. (like a plastic bag)

 

[jcappeljr]

Try replacing the rubber fuel line that goes from the primer pump to fuel filter canister.They crack and suck air.

 

[Monkeyboyarmy]

Rumor is that the pick up tubes in the tanks fail also. My wrecker was running great and one day it quit. Couldn't get fuel up the the pump. Transfered the fuel to the other tank and fired right up. I haven't pulled the other tank apart yet but suspect the pick up tube.

 

[infidel got me]

Run a hose before the lift pump and manually prime it.(FROM THE INLET SIDE OF THE LIFT PUMP INTO A CAN OF DIESEL FUEL) If it runs- then you just eliminated half the fuel system. Good luck!

 

[MtnSnow]

I've had the fuel pickup tube inside the tank break it's solder joint and suck air.

 

[Suprman]

Did you loosen the bleeder screw top back of the ip towards the front 2 turns should do it. Then press the primer pump a 100 times or so. You can also air prime if you have an extra fuel cap you can drill a hole and put a schrader valve stem in.

 

[74M35A2]

All points mentioned above are very strong candidates from having them happen. Another possibility is that your PCB is on its way out. Check and see if the lights on your CTIS module are lit up after you release the starter switch back to the run position. If not, then your PCB or an input to it is not behaving (oil pressure or alternator rotation signal, I think). This would de-activate the fuel cut solenoid and stop the engine after a start (if it does start in the crank position). Mine is doing this occasionally now, so I know it needs work (new solenoids).One member also had the connection from the fuel stop cam to the IP pump strip out, and he was unable to shut his truck off due to it, I think it is spring loaded into the run position, but yet another thing to check.

 

[TexanOnTheMove]

My CTIS lights all started flashing a couple months before my truck failed to run. I checked for air leaks, but couldn't find any. Anytime I drove my truck, all of the CTIS lights would start flashing almost immediately and would not stop. Could this mean my PCB is going out?

Thanks

 

[Suprman]

No

 

[TexanOnTheMove]

Then what is causing my all my CTIS lights to flash?

 

[Andyrv6av8r]

Then what is causing my all my CTIS lights to flash?

opcorn:

That's an entirely different thread.....my guess is you have a leak somewhere.

 

[Suprman]

Does just hwy flash and it do an initial pressure check once air builds to around 120psi then flash? Or do all 5 flash from initial power on?

 

[TexanOnTheMove]

All 5 flash from power on.

 

[Suprman]

That's a hard fault. Bad controller bad valve body or bad wiring.

 

[TexanOnTheMove]

Success! The rubber fuel line going from the water separator to the lift pump was dry rotted and leaking. I didn't noticed it at first. Had another one fabbed up at Ace hardware, installed it, bleed and primed the IP and the truck started right up!

Thanks everyone for the troubleshooting ideas!

Now I have to figure out why all the CTIS lights are flashing.

 

[Suprman]

Check the rear wheel valves they are mounted on a stem coming out of the hub it's a friction fit and from driving centrifugal motion causes them to slip up and fill air will leak. It's hard to see unless you are right down there and get your hands on the valve.