kawi600

Ive got a fuel system air leak someplace thats driving me insane. I replaced the fuel lines from the tank to the cab with good quality hydraulic hose push-lock fittings and vulcan draw straw 2 pickups so that part I can safely eliminate. All the stuff under the hood is now suspect. You folks have any tips on things to look for? Im most interested in any of the resident mechanics here who might have a tip for tracking down air leaks.
BTW, I can say the heater isnt melted, thats a common one.

waldersha

If you've replaced from the tank up to the cab, I would start with the return line where it attaches to the pump and follow it back to where your new lines start. If you've replaced all the way to the front (pump), then heater (you said it isn't that) or lift pump check valves might be the next suspect.

TIMMY22

ditto the last post. go all the way.

also, the overflow valve.

is this happening when it sits overnight?

you can check to make sure it's air by connecting a 6' piece of clear tubing to the return line into a bucket and look for air bubbles and/or foam.

also, you can pressurize the fuel tank and listen and/or look for leaks in the lines/fuel system. doesn't take much.

kawi600

It loses prime overnight and air will creep in. within a couple hours youll notice a stumble shortly after it starts.
Ive replaced and re-clamped all the hoses in there, replaced the lift pump and I still cant figure out where its coming from. It must be a very small leak.
You can really notice it under load where the fuel pressure dips towards 10psi. not good!

Crimedog

If your fuel pressure is dipping that low I would suspect the overflow valve. Do a search for Marty Tompkins and you can get one from him for about $35. You could try temporarily crimping the return line to see if your fuel pressure jumps up. If it does then your OF valve is the suspect. If you haven't replaced yours yet it is probably time to.

kawi600

Replaced that too.. bought the original cummins part and stretched the spring on my old one to 12mm as a test. No dice! Its got to be something less obvious like a crush washer or something.

1-5-3-6-2-4

I'd put positive air pressure to the tank and find the wet spot. regulated to about 5psi, no more.

troutbum

I have the exact same problem... trying to trace it down sucks...let us know what you find.

kawi600

I put clear plastic mercedes diesel filters in each hose run and it looks like the lift pump or filter is the culprit.
I bought a new filter drain / WIF assembly from cummins figuring thats a likely source for air.