The homemade testers made out of hydraulic pumps differ from the "factory" testers in that the "factory" testers provide a quick pressurized burst of fuel with each pump stroke, much like the output of the engine's IP. A hydraulic pump gives a continuous pressurized flow of fuel. Possibly this continuous flow might be able to "fool" an injector in certain situations.
Can you try short taps on the handle to try to mimic the output pattern of the IP?
Of course others have had good results using homemade pop testers, but I wanted to bring up an important difference.
My experience has been that injector peeing is caused by scored or worn needle, dirt, or needles mixed up from their matching nozzle bodies. One test is to hold the nozzle body at a 45deg angle and slightly insert the needle; it should slide all the way down until seated via its own weight, lubricated only with diesel fuel.
I had intended to build a POP tester, but never got it done. Hopefully soon.
Anyway, I would think it would be easier to observe things like a spray pattern with slower, longer pressure pulses. It might be difficult to observe fine issues with the spray pattern with only a short burst.
I assume spraying pressure is slightly lower than the peak opening pressure.
I just registered to say thank you for the warning, also I never knew about the grease guns or paint guns danger either.
After reading this post, I scrapped my plan to make one from a bottle jack (required some welding) and will be making one from a porta power as shown here.
Also I plan to build a safety shield out of plexiglass to put between me and the tool. (not sure how thick the plexiglass needs to be, or if I need to use a special type or anything.)
I would still need to reach around the glass with my hand to work the pump though, I am thinking the following:
1. get some kind of industrial heavy duty gloves that would protect my hand and arm, maybe heavy duty chemical gloves or something?
2. put a slit through the glass just big enough to work the pump handle up and down, and put some kind of flexible shroud, like car shifters have a rubber boot type of thing.
3. or I could weld onto the pump handle so that it forms an "L" shape so it can come around the corner of the glass and I can pump it from there.
I just want to make sure that we stay safe while using the tool, but I still fully intend to build one, just because there is many things in life that can be dangerous if you don't use the proper safety and precaution (like getting under a vehicle that is not supported by jack stands.)