Are you talking about one of these?? If so.. that's an interesting machine!
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If you have already tested pressure, that's good. Where did you test it, though? Assuming the test location gives us a pretty strong indication that the pressure is making its way to the valve in question, the 2 main possibilities that remain are leakage across the valve, and leakage across the cylinder piston seal.
Testing the valve CAN be fairly easy because you can probably swap hoses to a different valve on the valve set and see if that valve gives a different result. If it does, the problem is in the valve set. If it doesn't, the problem is in the cylinder. If swapping hoses around (at either end, mind you, it's possible your bucket cyl hoses might have the same ends and be able to reach back to your stick cyl if the hoses are long enough, and that might be easier than doing it at the valve set if the valve set requires funny shaped tools you don't have) is not easy, you can also test at the cylinder itself, but you need a plug to seal off the base end of the cylinder.
Cylinder piston seals are a fairly easy thing to test, because if you cap off the base end port and try to retract the cylinder and it starts to leak that pressure across the piston seals, it will actually start extending the cylinder back out again as the base end pressurizes. The base end generates more force at the same pressure because none of the piston is 'blocked' by the rod sticking out of it. So put same pressure on both sides, rod extends! That's a sure sign of a leak across the piston.
So:
Step 1: make sure the pressure you checked has no way to leak off before it even gets to the valve in question.
Step 2: choose to either rule out the valve by switching which valve is hooked to that cylinder, or rule out the cylinder by capping the base end and trying to retract it.
Step 3: Act on those results.
