Amos

I have a problem with my 1995 12 valve. Without warning the truck will shut off while driving. Doesn’t happen for a few days then all of a sudden will happen. Sometimes happens on the highway, but also on two lane roads. On the highway it’s done it several times at 70 mph, once around 75, once at 60. On a back road I was going about 50 mph and it also did it. Weather doesn’t seem to matter. Did it in rainy 40* weather, and also today about 62* and bright sunshine.

The truck just dies and you coast to the shoulder. Can then restart and continue driving. Sometimes with no further trouble, other times within 10 minutes it happens again. One time I stopped for fuel after it happened and it sounded like the fuel filler cap was under vacuum when I opened it up – made a hiss or whoosh sound. But this doesn't happen all the time - just once that I noticed.

The problem definitely seems fuel related, but not sure what to check next. I’ve already replaced the fuel filter. Years ago I replaced the rubber fuel lines with the Foster(?) kit but it’s been 8 years probably. Anybody run across this or have any suggestions? Also any chance it could be computer related? I don’t seem to have any electrical issues and the truck has new batteries. Any help is greatly appreciated.

patdaly

If it just shuts off like the key switch was turned, then you likely have an issue with the hold circuit.

p7100 trucks have 2 circuits for fuel, a Pull and a Hold, the Pull circuit is a higher amperage one that physically pulls the shut off lever up, then when the truck starts, it disengages, and the hold circuit ( lower amperage ) hold it in place until you shut off the truck.

Good thread to start troubleshooting.

https://www.dieseltruckresource.com/...ooting-279255/

gorms

Edit wrong thread!

What patdaly said.

Amos

It doesn't do it all the time and I still have headlights, dash lights, etc.

But the engine is stone dead as if the key was turned off. Does that change any opinions? Thanks for the info so far, will take a look and see what I find.

gorms

If it happens again before you get to look at it, leave the key on (don't try to start again) and go see if the plunger on the shut down solenoid is all the way up. If it fell down, raise it with your hand and see if it stays up (there is a spring to overcome doing this). May be some crud keeping it from raising fully, torn rubber boot etc. Then just the right bump in the road could drop the lever and shut it down.

patdaly

Yep, it is either what Gorms said or a hold circuit issue, those are the only 2 real possibilities.

Amos

Thanks everybody! Found the old FSS was the problem. The boot was destroyed and when I took the old solenoid off the entire thing fell apart in my hands. The new one is on and the truck is back on the road.