Hey guys, I have a 1999 Genie z45/25 boom lift that I can not seem to find the problem with. Everything works as it should with the exception of the primary boom lift, it will raise fine, but as soon as you release the raise function, it drops back to the ground immediately. I have replaced the primary cylinder seals, switched around the spools and solenoids and checked the orings and nothing seems to help. If you raise it all the way up, it will stay unless you extend the basket about halfway and it will just start falling again. The secondary boom and basket rotate all seem to work fine. I am a couple hundred miles from a dealer so I would appreciate any help you all can give me.
It sounds like the counterbalance valve on that cylinder is not working and it's coming down too fast to test it. If memory serves, the valve is a cartridge on the base of the cylinder near the hose fittings. Looks l like a adjustable valve cartridge. If this valve is working you should be able to raise the boom a couple inches, disconnect the hoses to the cylinder and the boom shouldn't move. They are often called holding valves as well. Be sure to use all appropriate safety precautions.
I also have a Genie Z45/25J before one year. On a day to do some tree work I have raised both the Primary and Secondary booms and only the Primary boom retracted when I desired to come down. The Secondary boom shows like it wants to retract with a slight movement but it doesn't work. I was in an urgent work and one of my colleagues has arranged a boom lift on rental . Then after we have checked our boom lift and the problem was with the hydraulic fluid level. Maybe you too have the same issue. Just check it.
Did you ever solve the issue? Mine just started doing the same thing. As soon as I let off the lift control the boom starts dropping just as fast as it went up.