Losing Prime again and again....MTDI AHU

[avocado]

Hi

I put a AHU in a Suzuki Sidekick.  Bought amanual pump from a fellow on here and the little truck runs great!  Well...most of the time.

It seems to lose prime at really weird times. 

I recently put a clear fuel line (  5/16") between the fuel filter and the pump in order to see what the hell is going on.  I have found that sometimes after sitting the fuel line is completely empty of fuel.  I cannot figure out where the air is coming from...all lines are tight and new. 

I was wondering if the fuel is just pulling out of the line (air coming from the IP side after shutdown?) and going back into the tank. 

Should I put a check valve in the line at the tank to make sure fuel is only going to the engine and not back into the tank? 

[gldgti]

check the injector return lines, and other return lines. when swtiched off, it will allow air in and all the fuel will drain backwards.

[avocado]

Wouldn't it be easier to just add a check valve? 

The thing is that I remember having put my return line into the tank at a pretty high level, so it may be sucking air from back in the tank...

[D.Loops]

air in the fuel would be a problem for starting must be sucking air from somewhere or fuel could be leaking back to tank could try a non return valve?

[westyventures]

Check the pump shaft seal.