M1008 idling good but engine shut off driving.

[MattTurbo]

Hello everyone, I need help with my new M1008 I bought last week.
Till yesterday everything was fine and the truck was running great.

Yesterday (after 2 days of rain) I fired up the engine and let it idle for 5 minutes. Started at first try as usual.
Then I put it in drive mode, drove for 30 feet and the engine shut off immediately.
I turned it on again but this time I was able to drive 100 feet and it shut off again.
This again and again for the whole afternoon: engine was very difficult to fire up, but then it was idling good even at max rpm, engine shut off after few meters when switching to 3rd gear or going over 25mph or on a light slope.
Road assistance tried to figure out what the problem was:
- fuel filter is ok but it has been bypassed just in case
- mechanical fuel pump on the tank is ok and working
- no water in fuel tank
-electrical connections on the fuel injection are ok
- air filter is ok

Do you guys have any idea of what the problem might be?

 

[NDT]

The injection pump has a lot of plastic parts inside which do not have infinite life. Personally after 10 years after overhaul I expect the pump to leave me on the side of the road.

 

[Keith_J]

Injection pumps before 1985 may have a flex ring which breaks down, plugging fuel return check valve. Fuel must flow, otherwise the plunger chamber cannot fill when transfer pressure equals case pressure.

When engine is cool, two solenoids are energized, one is external and holds the throttle open. The other is internal and holds the fuel return check valve open. This internal check valve opening can allow fuel to flow even with flex ring frags blocking the valve.

The wire supplying the cold start current is green.

What year model? There is a tag on the driver's side of the injection pump, what is the pump specification code? It starts with "DB2829-nnnn", if you can read "nnnn", I can determine if the pump has the flex ring.

 

[MattTurbo]

This are the best pictures they sent me for now. Vehicle is 500miles far from home.

 

[Keith_J]

4267 does not use a flex ring, that is the original 1984-1985 IP for a CUCV. The US military superceded this with the 4520 and eventually, 4521 which is a JP8 upgrade.
I've yet to find a CUCV specific model using a flex ring. It is possible one could have been fitted, every Stanadyne approved rebuild uses the elastomeric insert drive upgrade.

 

[87cr250r]

This happens when the injection pump drains while parked. This usually happens over night. The engine starts and idles fine but will die once a load is applied. After up to a minute or cranking, similar to priming the fuel filter, the engine will start and run fine for the rest of the day.

There are two components that cause this drain without external leakage. First is the lift pump, it has check valves. Second is the throttle shaft seal on the IP. This let's the air in. There are no "plastic" components in the pump. Most other seals on the pump will leak fuel out when bad, not air in.

 

[MattTurbo]

This happens when the injection pump drains while parked. This usually happens over night. The engine starts and idles fine but will die once a load is applied. After up to a minute or cranking, similar to priming the fuel filter, the engine will start and run fine for the rest of the day.

There are two components that cause this drain without external leakage. First is the lift pump, it has check valves. Second is the throttle shaft seal on the IP. This let's the air in. There are no "plastic" components in the pump. Most other seals on the pump will leak fuel out when bad, not air in.

Thanks for the reply.
Lift pump is good.
Anyway last Tuesday the truck was transported to a mechanic in Germany. Next week I'll have some news...I guess.