Hello I have this Diesel fuel injector pop tester



But I cannot get the unit to maintain pressure. I no longer have the instructions either. It has been used one time before. The lever moves up and down freely and I think the plunger or internal unit that pumps the fuel up is stuck at the top of the unit. I cannot get inside to release this and I am not sure if this is the best way. I have located on the back of the unit a screw with a ball check valve inside. I have not taken that apart any further but I believe that may be the cause or solution to my problem . So basically I cannot maintain or achieve any pressure. I pumped the unit yesterday and it finished the last 10% on the lever, then became stuck. So it seems it is fully open. or the plunger is at the top. I am be completely wrong though. So I am trying to figure out how a check valve would work on this unit or if anyone else owns this unit and has any further information. I believe these are fairly popular on the forums.

Thank You.

Edit; My unit does not have the knob on the right hand side.
Edit. I should have put "tester" in the title, D'oh!