GearHd6

I have a 96 Cummins Dodge and about 3 weeks ago it mysteriously started losing it's prime. If it sits overnight it needs to be manually primed in order to start. The longer it sits the more air it gets in the system. Does anyone have any ideas. Thanks.

infidel

Replacing the rubber hoses at the rear of the engine is a good start.
Make sure to use diesel rated hose, preferablely USCG rated fireproof.
You will need about two feet each of 5/16 and 3/8" or buy a kit here
http://www.fostertruck.com/dodge/default.htm

GearHd6

Is there anything in the fuel tank that can cause the problem? Im going to dive into the repair this weekend and I'd like to get all the possibilities together before I attempt to work on it. Thanks

RCW

The fuel hose replacement suggestion is the usual fix. But, go a bit farther and replace the hoses on top of the tank, too. Also, pull the fuel sender and replace that hose. It eventually cracks and allows air into the system at about 2/3 of a tank of fuel.

The other very common cause of loss of prime is a broken spring on the overflow valve. The 96 has a two piece overflow valve located on the inside of the P7100 injection pump. Clean the area throughly, then pull the smaller of the two bolt heads and you will extract a spring, a follower, and a check valve. If all is well the spring will be in one piece, if it is in two pieces then it is time for a new overflow valve.

The 94-98's also have a propensity for developing a leak in the fuel heater where the wire connector penetrates the housing. The fix there is to pull the connector plug and liberally apply a dab of dielectric grease then plug the connector back in, and that generally stops the air infiltration. Sometimes it is necessary to replace the heater unit, but not often.

mx261

start with the easy stuff first, mine did that and it turned out to be the fuel filter. Thats prolly the easiest to change. mine had a wierd gap in the gasket. hope this helps

vssman

All good tips given above. Most common cause is the rubber hose at the rear of the engine behind the fuel filter. If it were me, I'd start there. Get a new filter as it has to come off to get to the hoses. Some have found it easier to remove the master cylinder from the mount and let it rotate toward the fender for more room. Make sure to get good hoses (like marine rated fuel line) as you only want to do this once...

Rockyhud

I agree with vssman; that fixed my truck with the same problem. Start with the fuel hoses from Foster Truck. To make it easier to see and replace these hoses I'd recommend removing the fuel filter canister (and replace the filter while you're doing it). I fought trying to get to the fuel return hose that runs along and under the side of the intake before finally deciding to remove the canister. What a difference that made! Doing this also lets you see if there's any sediment in the canister that needs to be cleaned out so you start back up with a clean system and that's a good thing.

Steve

rharveysr

Here is another one for ya! Mine did that when I would park it with the nose up hill...but when I parked it nose down hill it would start with no problems. I called Cummins and told them what it was doing and the first thing the tech said was that the fuel pump is not hold prime with the nose up hill...
I replaced the pump and it stopped it... I had just replaced the fuel lines before we went on the trip so I knew that wasnt it.
Anyway just another item to check...

Rick

TRCM

on the overflow valve, you will actually extract 2 small spacers, a spring, and the ball. Don't mistake the spacers/shims for a broken spring.

GearHd6

Could someone tell me where exactly on the injector pump that overflow valve is? I dont want to take something apart I shouldnt be. Thanks again.

infidel

The object in the lower left corner is the oil fill cap.


Sometimes the valve hits the engine when you try to take it out.
Don't make the mistake of bending the steel line to get it out, you will have a very hard time lining it back up again. Instead file or grind the cut out in the manifold so the valve clears on the way out.