Air in fuel system? Why or how?

[cjfarm11]

Workin on a 1999 with a fresh rebuild with around 800 miles on it. Ran great tell now. After some tinkering around i found air in the fuel causing the engine to run rough and die. Bleed the air out and it will run fine. Question is how is it getting air in the system? Installed all new injectors and cups at rebuild. ANy info or ideas is appredciated. Thanks

[NorCalDiesel]

With just 800 miles on a fresh rebulid I would bet it had some air in the fuel system from reassembly and it just now made it through.

Otherwise you have to have an open system before the heads, but most likely before the fuel pump.

[cjfarm11]

So are you thinks maybe something inside the Tank?

[NorCalDiesel]

Originally Posted by cjfarm11

So are you thinks maybe something inside the Tank?

Well, I am saying it is entirely possible that you just had some air in the system from the rebuild. Otherwise you could have a leak on the suction side of the fuel system which is from the pump back to the tank. It is common for the duck bill style intake inside the tank to allow air inside. There are some of us that have modified the in-tank pickup due to this general problem. It could also be the quick disconnect on the intake side of the pump.

If you bled the air out and it runs better and stays that way then don't worry. If it still has air being introduced then you need to start looking at the fuel system.

[cjfarm11]

I can bleed the system and it will run fine for a few minutes and then it starts running rough again. I guess and going to pull the tanks and start there and work forward.

[sho669]

You could also be getting compression/exhaust leaking past the copper washer on the bottom of the injector geting into the fuel system.

Usually happen when they're too loose. You can do a balloon test on each bank to verify if it's the issue or not and/or just double check the torque on the injectors.

Not discrediting any of the info you've been given already just adding something else to the mix. Personally I delete the "mixing chamber" whenever I have a tank down and throw a little filter inline before the pump.

[cjfarm11]

Last night i did eliminate the in-tank mixing deal. did the hutch mod. and the problem continues.

[SledDogg]

Did you eliminate the mixing chamber? If not drop the tank, and pull the bottom off the mixing chamber so as too get at the two screens. Pull them and have fun cleaning them!!! They just caused me a crap load of money out of pockets replacing wrong parts. Mileage is up now and my stage 11 single shot sticks are you quiet now. Full fuel pressure.

[LilBlack]

My 7.3 had the same problem, after I replaced my trans.

Turns out I had ripped my underbody hose that runs right by the frame and it was pulling in air.

Maybe this could be you.

[purplepstroke]

Sound like compression coming up through the injectors washers or cups to me.