Engine/Transmission (1994 - 1998) Starting issue

[LNaugle]

97 truck when parked uphill overnight, starts and dies. seems fuel in p7100 is what is startind on then loses prime... doesnt seem to lose it completely cuz dont have to bleed or crank THAT long to run again... double checked fuel lines from tank to motor with psi applied to tank... no leaks... checked fuel pump psi found low replaced it and the inlet hose... replced fuel filter... replaced overflow on p7100... was fixed for about 3 months then started doing it again... replaced overflow with TORK TEChnologies valve and replaced fuel cap thinking maybe a vacuum was happening, still does same thing. starts fine on level ground or backed into driveway. does not have the problem any other time just over night. truck runs great also. what am i missing?

 

[mwilson]

Low fuel level in the tank??



Hole or crack in the plastic line on the sender/fuel pick-up in the tank???? OK as long as there is fuel above it.



Mike. ??

 

[Missouri Mule]

Usually when you have symptoms like your's, the problem is a fuel line usually the return fuel (rubber) or the lift pump. The rubber return line can develop hair line cracks in it which sucks air in but not fuel (on my truck it did leak overnight, but I had same symtoms you had except had to prime now and than). The liift pump has check valves in it (3) if they go bad (damaged) fuel can leak back to tank.

 

[BigPapa]

Fuel heater/prefilter or return fuel line.

 

[LNaugle]

i pressured up yhe return line and doesnt seem to have problem... was thinking fuel heater o-ring but odd how it went so long with out problem then came back... got fuel pump from genos i think, will have to look up ticket, but cant imagine the check valves in the pump bad again and causing same problem again... anybody else use genos pump?

 

[LNaugle]

also fuel level makes no diff and only happens when nose of truck pointing uphill...

 

[GAmes]

Try pressurizing the supply line with regulated air about 25 psi. Look for leaks at the prefilter/fuel heater o-rings (throw away the fuel heater puck), the supply line fitting that goes into the prefilter, the 90* elbow to the lift pump and the fitting that you had to swap into the new lift pump.

 

[surfbeetle]

Missouri Mule is right, this is a common known problem with the 12 valves. I have changed my hoses several times over the last 17 years. You can get the more expensive lines from Larry B's, those just mean that you won't need to change as often, but you still get the displeasure of doing it. The lines run along the drivers side of the transmission up to the engine.

 

[fest3er]

i pressured up yhe return line and doesnt seem to have problem... was thinking fuel heater o-ring but odd how it went so long with out problem then came back... got fuel pump from genos i think, will have to look up ticket, but cant imagine the check valves in the pump bad again and causing same problem again... anybody else use genos pump?

It may seem odd, but try putting vacuum in the tank. As mentioned, fuel draining back to the tank is most often a failure in rubber hose (and less often rusted-out hard line). The rubber hose won't necessarily leak fuel, but it'll let air in (vacuum).



Let it go a while longer. You'll soon have fuel everywhere and the source will be easy to find.

 

[hsmith]

Don't forget the connector at the heater. Common place for a leak. As Gary says, chunk the heater.

 

[surfbeetle]

Let it go a while longer. You'll soon have fuel everywhere and the source will be easy to find.

Only if it's the hard line leaking, if it's the rubber lines I am referring to, you won't see a leak until it actually breaks. When they start to get brittle, they just let the air in and the prime out.

 

[LNaugle]

pressured everything before and changed the big rubber line when did the pump... everthing was ok for 2-3 months then started doing same thing again... . the only thing i havent tested is the fuel heater seal... . which obviously passed psi test before... i am very familiar with 12 valve trucks because they are the only cummins i have personally owned since 93... . had an 06 and sold it before i drove it and now have a 03 am building a motor for... WHICH is why i am asking for help... . had it fixed then started again... customer says if he parks flat or backs up his driveway there are no problems... had other trucks with somewhat similiar symptoms fixed with things you all are suggesting... maybe a hose clamp came loose or seal in fuel heater starting to go n happens to be causing same problem... . thank you all for the suggestions... . will let you know what i find...