Air Leak

[bbboomer]

I have a 1984 300SD with a Frybrid kit and loop return.
I have been having air leak issues for a while now and I have checked and rechecked everything several times. I cannot find any leaking connections, hoses etc.
It does seem to leak worse on VO than on D2 but it leaks on both. I have clear filters on both return lines so I am sure it is getting air in the system.
I have the looped return disconnected for now to help eliminate any air that does find it's way into the fuel system. I could not see any return to the VO tank with the loop hooked up. Should there be some?
Has anyone ever had air leaks internally at the lift pump? I don't know where else to go from here.
Darrell

[cgoodwin]

How do you know you have air?

[bbboomer]

I have clear filters on both returns.
The engine will miss and air bubbles will show in the return lines.
When running tiny air bubbles can be seen in either filter and lots of air is seen when switching fuels.

[cgoodwin]

Is your lift pump the old style with the knob you unscrew?

[bbboomer]

Chris,
It is the new style Bosch primer pump and was replaced a few months ago.
The original primer pump had already been replaced with the new style pump.
It does the same thing with both old and new primer pumps.
I have replaced the VO filter and re-tightened the filter mount stud in the heated filter housing.
I replaced the o-rings on the diesel filter banjo bolt.
I replaced the rack damper screw, a common cause of missing at idle.
The car runs good most of the time but intermittently it is leaking air and only noticeable at idle.
I have tried everything I can think of short of replacing/rebuilding the pump.

[SunWizard]

Move a clear inline filter around. When you get to a part where there is air after, and no air bubbles before, you know exactly where the leak is.