Hello all..I have a 644b-42 with the Cummins motor and mid inlet hydraulics. I had a problem where the engine was laboring and oil was getting hot. JLG sold me on a new golden valve block that bolts to the front of the pump. I still have a long delay on start up and frequent surging. I had a hydraulic shop confirm accumulator is in spec but it still seems to me this machine is trying to pump too much oil and bogging it down. Is there a way to test standby pressures out of pump 1? I have compression tested engine with good results, rebuilt injection pump and new injectors so I feel engine is not an issue. Is anyone familiar with the hydraulics in this machine that can offer me some help?
I'll try to help you. We need your serial number. Is the engine turbo or natural? Do you have pressure test equipment? What symptoms did you have to cause you to put the upgraded charge valve kit on? Would all hydraulic functions come and go while you were operating it? What was your accumulator pressure when it was tested? The actual standby pressure. Have you checked the accumulator charge valve block (the one the new 53 inch long hose in the kit hooks to)? Have you checked pilot valve pressure? Do you hear any hissing while it's running and cycling? If so put your hand on the different valves and feel for heat differential. Make sure the frame tilt lever isn't hung partially open. Also the brake pedal as well. It's going to be a witch hunt.
Thanks for any help you can offer. Finding anyone who knows much about these has been difficult! This machine has been bugging me for the couple years since I bought it. I have two other old highlanders TT-34’s that can run circles around this one! My serial number is 99z24n21-812. It is naturally aspired. I have test equipment and have recorded that rear OC1 cycles between 1600psi and 1000psi every 45 seconds when oil isn’t real warm. rear OC2 does same thing. I notice 400psi in this port with engine off but key in on position. Brake pressure records 250psi which seems low according to my service manual says should be 330. Brakes do seem to work well. Steering is 2450 when I dead head it. Pilot pressure was 400 and I adjusted it up to 450psi spec if I tightened the proper relief (the one on the pump). Accumulator also bounced between 1600 and 1000psi every 30 seconds or so with room temp oil. My original symptom was hissing and I noticed the return pipe to tank would get very warm to touch in no time. Since installing new block my oil is cooler and no more hissing in steering circuit. I believe my issue is something still causing the engine to labor. It’s difficult to start. It’s like it fires and dies. I have to run the starter longer to overcome that for it to start. Once started the machine takes 30 seconds before it will make the cycling noise and function anything. Is that normal for this machine? How would I check standby pressure? Looking at my hydraulic schematic it looks like pump 2 takes the lazy route through the open center main valve bank. I see pump 1 sends priory oil to steering and has to satisfy a lot of other stuff before sending oil to “Excess Flow”. I’m not sure what to check next for possible internal leakage based on my findings so far?
I think your hard start issue may be the unloader valve in the control valve stuck in load position. Sent you a PM.