Leaky Tester

[AUDIBLE]

I posted this as a reply to the DIY pop-tester-maker, but thought maybe it should be here instead. Apologies if this is a no-no.

I used the great DIY pictorial to build a pop tester.

I built the tester as described, and pumped about a cup of diesel through, and everything seemed good. I attached an injector and tightened it, but found that the pump was not holding pressure. The gauge showed pressure on each down-stroke of the pump, but fell off immediately. There was some resistance from the pump on each down-stoke, but the pressure never got above 3-400psi, and would immediately drop back to 0.

If I fill the low-pressure reservoir section of the pump too full, the diesel leaks out of the top, at the seam where the jack-bolt contacts the bottle. It doesn't leak here during the pressure test, so I'm thinking that even after I seal it, it won't affect the non-functioning of the jack.

There are no diesel leaks anywhere in the visible portions of the high-pressure parts of the system.

Aside from replacing the whole pump, does anyone have any ideas about where the pressure could be failing? I only can think if the pump piston, the check valves and the threaded bolt seal. But the pressure falls so quickly, I have to think the pump is defective.

Ideas most appreciated!

thanks