Air intrusion making me crazy

[quickster]

Hows it going all. Just installed a rebuilt IP and having a hard time getting it to stay running. I installed new olives on the hard lines, and everything is tight. I got it going and was running fie,but the idle started oscillating up and down, then sounded like it running out of fuel, then died. Pulled off the filter and it was half full. Put on a clear return line from filter head to the injector and I'm getting spurting air. Filled the filter, bled out a couple injectors and got it going. Started with the air again-fuel for 2 seconds then air-fuel two seconds then air. Stayed running for a while but the idle got erratic like it was running out of fuel, then died.
I changed out the return lines last winter, the o-rings on injectors today. New fuel filter , what else? The only hose I didn't get to yet is the one leading to the lift pump from the hard line. The one thing I don't have is the check valve on the filter head. That would be in the brass 90 fitting with the return line, correct? If this could help me out, where can I pick one up?
Also, the plastic caps should snap down oner the two orings,correct? They are a ***** to get down.
Anyway, some feedback would be helpful. Almost all day working on this and still not right. Think International might have a check valve?
Thanks Jack forgot--this is for the '87 6.9

 

[laserjock]

I find it odd the filter is half empty. How's the lift pump? Tanks full of fuel?

 

[quickster]

lift pump brand new, and the tanks are full. The fuel is getting pulled from the filter- I checked it . Filled the filter up, and I have the clear line to the return. It pulls fuel solid-no air, then as it goes down it's solid 2 sec then air, 2sec then air. Like the filter isn't filling fast enough. I put the lift pump in before I had the IP rebuilt. I actually unscrewed the filter and cranked the motor over to see if fuel was getting up there. And it is, so the only rubber piece left to change is the one between the lift pump and hard line. Either that or it's pulling air someplace else. O ring on the fuel heater? Haven't checked that yet.
I have so much time into this POS I'm wondering if it's worth it.

 

[bbjordan]

Divide and conquer

My guess is that it is sucking air before the lift pump. Air intrusion is not a problem on the pressurized side of the system.
To confirm it is on the suction side, run a hose from the intake side of the lift pump into a bucket of diesel and see if the problem goes away.

Does your truck have the remote water/fuel separator? Because that can be a problem. I can't remember what year they changed over. I think it was 1987.

 

[79jasper]

Replace the rubber line right before the pump. They're known to cause issues when they have some age on them.

Sent from my SM-T537R4 using Tapatalk

 

[quickster]

going to replace the rubber line at lift pump. That one is tough to get to. I bypassed the water separator long time ago. If still a problem, going to have to check the fuel heater.

 

[franklin2]

My guess is that it is sucking air before the lift pump. Air intrusion is not a problem on the pressurized side of the system.
To confirm it is on the suction side, run a hose from the intake side of the lift pump into a bucket of diesel and see if the problem goes away.

Does your truck have the remote water/fuel separator? Because that can be a problem. I can't remember what year they changed over. I think it was 1987.

Listen to the above. You are all around the filter area, but the classic "air intrusion" problem only happens with the engine off, and it sits for awhile. Your problem sounds like it's sucking air from the suction side of the pump. That would be any line/valve, fuel tank problem BEFORE the lift pump.

Take a straw, plunge it in your Coke, put your thumb over the end, and pull the straw out of the drink. The drink stays in the straw as long as you hold your thumb over the straw. That's how these fuel systems work, they need to be sealed or the fuel will run back down the return line and into the tank. But this is only a problem with the engine off. You have some other problem.

 

[quickster]

going to run a hose into jug of diesel. I pressurized the return side and it's tight. Either the lift pump is not pulling enough, or there's a problem in line. I tried both tanks- same thing.

 

[IDIoit]

if its a stock water fuel sep. by-pass it.
ive worked on 4 of these trucks, and they have always been a problem.
replace all rubber lines.
make sure none of them are kinked.

 

[quickster]

water separator long gone. goin hunting for leaks saturday

 

[RB9511]

I had a similar problem. Mine was the tank selector valve was leaking air in. I bypassed it by running a line from the font tank to the lift pump and I installed a check valve between the lift pump and the filter, I cut the hard line between the lift pump and the filter and put a soft line in and got a check valve from Napa. I hope this helps. I am no guru but I got mine to work.......

 

[quickster]

So I narrowed down the possible causes. I put a 5 gallon jug of diesel directly to the lift pump and it's perfect. No air. So I already tried both tank while it was running, and still got air, so yeah RB9511 it might be the selector valve. Or maybe the fuel line itself because it was replaced by the guy who had it before me. It is pretty banged up so I might just replace it. I'll post when I get it right.

 

[Shaughn]

I'm having the same issue I think maybe the soft line right before the lift is bad because I have replaced every single pieces of rubber in the fuel system other wise

 

[Oledirtypearl86]

I'm having the same issue I

Check that soft line then for good insurance get ahold of thewespaul and get on of his check valves they are awesom