air intrusion back again with a vengeance

[Austin86250]

86 6.9
well air is back in my system yet again kind of a recurring problem with my truck but this time is worse than ever

I put a clear line from the fuel filter housing to injector cap one and found tons of air
after that I put a clear line on the inlet of the mechanical fuel pump to the metal fuel line that goes to the tank and found tons of air there (I have videos if needed)

here's of all things done to my fuel system:
injector o rings, caps, and return lines replaced (four months 2000 miles ago Delphi brand)
replaced mechanical fuel pump (one month 800 miles ago also Delphi brand)
turned my injection pump up 2 flats (used new gasket)

using the process of elimination I'm lead to believe its either the fuel water separator or selector valve

thoughts?

 

[Cubey]

How full is the fuel tank in question? Are you parked on a steep incline? The fuel tank pick up "shower head" may have fallen off and will not allow you to pull the last 1/4 tank. That plus being on a hill (nose facing up, I think) will cause it to fuel starve especially badly at 1/4 tank or so.

Try bypassing your fuel tank selector valve for the tank you want to use with a log piece of hose between hard lines on either side of the valve. Very easy to do it that way.

 

[Austin86250]

How full is the fuel tank in question? Are you parked on a steep incline? The fuel tank pick up "shower head" may have fallen off and will not allow you to pull the last 1/4 tank. That plus being on a hill (nose facing up, I think) will cause it to fuel starve especially badly at 1/4 tank or so.

Try bypassing your fuel tank selector valve for the tank you want to use with a log piece of hose between hard lines on either side of the valve. Very easy to do it that way.

upon diagnosing both tanks completely full
by bypassing the selector calve wouldn't that mean only one tank? with how much i drive one tank is not practical

 

[Cubey]

upon diagnosing both tanks completely full
by bypassing the selector calve wouldn't that mean only one tank? with how much i drive one tank is not practical

Then just do it for diagnostic purposes? Using a spare piece of hose makes it easy to put back if that isn't the problem.

 

[Austin86250]

oh i see thanks for the tip
is it 3/8 line?

 

[Cubey]

oh i see thanks for the tip
is it 3/8 line?

You need 3/8" for the supply and 5/16" for the return.

 

[TNBrett]

Are you running the original water separator with the “pull the ring to drain” design? I’m not familiar with them, but they have a reputation for being a problem.

 

[franklin2]

I thought bypassing the original old water separators on the older 6.9 trucks was pretty much mandatory to stop fuel system leaks.

 

[Austin86250]

Yes I belive it’s the original “pull style” how do you go about deleting it?

 

[Austin86250]

Well now I’m very confused on where this air is coming from I ran deisel strait form a jug to the fuel pump and still have air
Could this be a faulty fuel pump?

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Update let it sit for 20 minutes and fired it up again to find no air in the system (still running of jug)

 

[IDIBRONCO]

Yes I belive it’s the original “pull style” how do you go about deleting it?

From what I remember, along the frame, coming from the selector valve toward the engine, there's a steel line that runs along the frame. I don't recall the exact location, but somewhere as it gets underneath the separator, the steel line makes a turn upward there is a rubber hose attached to the steel line and that goes up to the separator. There's another rubber line coming back from the separator that attaches to another upward turned steel line. The second line continues across the engine cross member and goes to the engine. What you want to do is to remove both of those rubber lines and connect the two steel lines with a piece of rubber fuel line.

 

[Austin86250]

Well I just kinda hooked it strait form the fuel tank to the fuel pump for now

 

[IDIBRONCO]

I guess you just bypassed the selector valve and the separator in one shot.

 

[Cubey]

Well I just kinda hooked it strait form the fuel tank to the fuel pump for now

That's how my RV was for a short time. It already had no water separator (was missing) and the tank selector valve was leaking pretty badly, so I bypassed it and continued to run on a single tank, until I finally got a new tank selector valve 2 years later (last year). I put in a Racor W/S too, although it's after the (electric) pump instead of before the pump, like it says to do.

 

[Austin86250]

Very temporary going to the junkyard tomorrow to find a selector valve Becuase Napa wanted 700$ for one or I’m open to other ideas on how to get 2 tanks as one tank isn’t enough for me