Archived fixed fueltank module now truck wont start

[Hootguy]

I've been chasing a loss of prime issue for the last 3 days now.

It all started with the fuel line steel inlet fittings on the top of the tank leaking,,I had a 2003 module from which we took the plastic inlet fitting unit and spliced it to the 96 inside module supply and return line,,took the module appart and cleaned up the filter screens,,,tested the inlet pipes to be sure our splice did not leak air and tested ok,,

While i was there,,changed the fuel lines from tank to pump,using a combination of braided line and a straight section of 5/16 and 3/8 steel fuel line. .

After all this work,,truck wouldn't start,,,would not prime at all,,so we pressurized the tank with a bit of air pressure,,,that got it somewhat primed and after some injector bleeding it started up,,but after letting it sit for 20 minutes it lost prime and would not start at all. ,

The filter was also replaced.

The next test i hooked up a small 12v motocycle fuel pump fed from a outside fuel container with both supply and return into it,,,and that would keep it running even when reved up... . then we disconnected the mootorcycle pump and just stuck the lines in the fuel container and reved up the mootor pretty good,,,a minute later the truck was dying almost stalled,,i kept a light foot on the throttle and it seemed to let the fuel supply catch up,,,but if i reved it up more it tries to stall...

This is making rip my hair outta my head,,which are hard to replace at my age,,

If anyone has any input i would GREATLY,,GREATLY,,appreciate it,,,

Thanks all. .

 

[Joe G.]

It sounds like an air leak in the fuel hearter/pre-filter assembly or the short curved hose between the pre-filter and the lift pump.

 

[Joe Mc]

It's possible that the tank is not properly venting and creates a negative pressure when running, then after turning off it sucks fuel back? Try testing with cap off. Have the cap checked or replace if needed.

 

[Hootguy]

Hi

Thanks for the replies. .

I have been testing with no cap on the tank,,,also with the lines removed from the tank and put in a seperate fuel container to eliminate the fuel tank module alltogether,,and it still looses prime.

I do have the fuel heater in,,it was removed when it caught fire 2 years ago,,seems to run fine without it,,other Cummins application dont have one,,,

I also replaced the rubber line between the fuel pre-screen and the lift pump. .

I am thinking of replacing the entire lift pump/fuel heater/stock fuel filter set up with a custom set-up using a heated Racor filter from the scholl bus place i friend works at and a electric lift pump,,,,any idea on which electric lift pump to use,,,i tested with a motorcycle pump which is about 7 psi...

I hope i fing the reason for the loss of prime soon,,,i need my truck.

Thanks again

 

[John Robinson]

Check your return check valve. If its seating good you shouldnt loose prime, "OR" your fuel lines that go on top of your transmission may have a hole.

 

[Hootguy]

I have checked the overflow valve right from the start,,looked good,,spring was a little over 1/2",,,

The fuel lines where all replaced and relocated away from the transmission. .

I replaced the lines with braided flexible lines and sstraight steel sections on the frame. .

 

[Hootguy]

Well,the truck seems to have fixed itself,,it started fine yesterday and seems to running ok.

Could a piece of dirt in the overflow valve have caused my loss of prime so quickly?

Or maybe an airlock in the lift pump??

I have to drive to Road Atlanta in 2 weeks for a motorcycle race and i need to have my truck be reliable?

Thanks a lot