-
Thank you for visiting HeavyEquipmentForums.com! Our objective is to provide industry professionals a place to gather to exchange questions, answers and ideas. We welcome you to register using the "Register" icon at the top of the page. We'd appreciate any help you can offer in spreading the word of our new site. The more members that join, the bigger resource for all to enjoy. Thank you!
JLG 40H problems and fixes
- Thread starter mark3885
- Start date
willie59
Administrator
The creep function is handy when you have boom extended a good bit, it allows you to move boom functions with a long boom and not get fast movement, which can be undesirable when you're near things with the basket.
With all the functions that are controlled by a PQ controller, you should be able to stroke the controller fully, giving fast movement, then flip the creep switch. You should notice a radical slow down of that function. If it's not working, that circuit is either not getting power, or the PQ controllers are not adjusted properly.
With all the functions that are controlled by a PQ controller, you should be able to stroke the controller fully, giving fast movement, then flip the creep switch. You should notice a radical slow down of that function. If it's not working, that circuit is either not getting power, or the PQ controllers are not adjusted properly.
cool thanks for the info.. you made me think of one other odd thing.. the lift up down control stick on the platform works.. but i have to hold the stick just a little off it maximum travel or the movement will stop.
is there an adjustment somewhere to fix that? .. i can live with it but every once and a while i move the stick to full travel and the lifting action comes to a jerky stop and will resume when i back the stick off max travel a little. I attached a few photos.. she won't win any beauty contests..
is there an adjustment somewhere to fix that? .. i can live with it but every once and a while i move the stick to full travel and the lifting action comes to a jerky stop and will resume when i back the stick off max travel a little. I attached a few photos.. she won't win any beauty contests..
Attachments
willie59
Administrator
Nice machine, 4WD with articulating steer axle. 
Sounds like you may have a faulty PQ controller, not unusual. First thing I would do is pop the lid open at the upper controls, disconnect the boom controller from the harness plug connection, and connect the boom harness to the swing controller. You can then connect the boom controller to the swing harness. Operate those two functions and see if the boom now operates proper and the swing operates goofy. This would confirm the problem is with the PQ controller and not a wiring issue.
The PQ controllers have operation adjustments. There should be 4 trim pots with adjustments screws labeled something like Lo, Hi, Mid (or Threshold), and Ramp. It takes a very small flat head screwdriver to adjust trim pots.
The first thing you do is back off all trim pot screws by turning them CCW. Those are 32 turn trim screws for full adjustment range, but most likely each trim adjustment will be somewhere in between 0 and 32 turns already. You need to be in a real quite place when backing off screws.
Turn each screw CCW until you hear a faint "click click" when rotating each screw. That sound is the adjustment at it's end. Don't continue turning much after hearing those clicks. Do this to each trim pot adjustment and you're ready to adjust controller.
Let's start with boom up/dwn controller. Have boom fully retracted, start engine. Depress foot switch and move boom up control lever about 15 degrees, what's called "notch off center", and hold the control lever in that position. Adjust Lo trim pot CW until boom just starts to get a boom up movement, no more.
Then, with boom up lever fully stroked, adjust Hi trim pot CW. At a certain point of adjustment, boom operation will speed up as screw is turned. Adjust screw CW until boom speed no longer gets faster, stop there.
Now, bring the basket back near ground and extend the boom a good bit, long boom. Flip the creep switch to creep position. Fully stroke boom up control. Adjust Mid (Threshold) screw CW until you get a desired slow boom operation speed.
Lastly, turn off creep switch, fully retract the boom, and turn the Ramp screw in about 10 turns for pre-adjustment. Fully stroke boom up controller to make boom move at full speed, then simply let it go so it returns to center. If boom abruptly stops, adjust Ramp screw a few more turns CW, try again. At some point of adjustment, boom up will no longer stop abruptly, but instead will drift for a moment and come to a slow stop when controller is released. Once you reach that point, adjust Ramp in or out to get desired power down that doesn't cause abrupt stop of boom movement nor does it drift excessively.
This adjustment procedure applies to each function controlled by PQ controllers. If the adjustments won't work out, PQ controller is faulty and needs replacement.
Sounds like you may have a faulty PQ controller, not unusual. First thing I would do is pop the lid open at the upper controls, disconnect the boom controller from the harness plug connection, and connect the boom harness to the swing controller. You can then connect the boom controller to the swing harness. Operate those two functions and see if the boom now operates proper and the swing operates goofy. This would confirm the problem is with the PQ controller and not a wiring issue.
The PQ controllers have operation adjustments. There should be 4 trim pots with adjustments screws labeled something like Lo, Hi, Mid (or Threshold), and Ramp. It takes a very small flat head screwdriver to adjust trim pots.
The first thing you do is back off all trim pot screws by turning them CCW. Those are 32 turn trim screws for full adjustment range, but most likely each trim adjustment will be somewhere in between 0 and 32 turns already. You need to be in a real quite place when backing off screws.
Turn each screw CCW until you hear a faint "click click" when rotating each screw. That sound is the adjustment at it's end. Don't continue turning much after hearing those clicks. Do this to each trim pot adjustment and you're ready to adjust controller.
Let's start with boom up/dwn controller. Have boom fully retracted, start engine. Depress foot switch and move boom up control lever about 15 degrees, what's called "notch off center", and hold the control lever in that position. Adjust Lo trim pot CW until boom just starts to get a boom up movement, no more.
Then, with boom up lever fully stroked, adjust Hi trim pot CW. At a certain point of adjustment, boom operation will speed up as screw is turned. Adjust screw CW until boom speed no longer gets faster, stop there.
Now, bring the basket back near ground and extend the boom a good bit, long boom. Flip the creep switch to creep position. Fully stroke boom up control. Adjust Mid (Threshold) screw CW until you get a desired slow boom operation speed.
Lastly, turn off creep switch, fully retract the boom, and turn the Ramp screw in about 10 turns for pre-adjustment. Fully stroke boom up controller to make boom move at full speed, then simply let it go so it returns to center. If boom abruptly stops, adjust Ramp screw a few more turns CW, try again. At some point of adjustment, boom up will no longer stop abruptly, but instead will drift for a moment and come to a slow stop when controller is released. Once you reach that point, adjust Ramp in or out to get desired power down that doesn't cause abrupt stop of boom movement nor does it drift excessively.
This adjustment procedure applies to each function controlled by PQ controllers. If the adjustments won't work out, PQ controller is faulty and needs replacement.
Last edited:
fletcherwrench
New Member
Hello . anybody ever experience backfire problems with the ford duel fuel 40H? it has an electronic ign. once the machine is up to operating temperature it coughs and sputters and backfires through the exhaust . does it on gas and propane.
I have a JLG 40 HA also it just started to act up the other day when step on the boom control in the bucket the gas motor throttles wide open. A tech told me to replace the governor didn't so a thing. Any body have an idea where I look next?
flhayman
Active Member
I have a JLG 40HA, Deutz Diesel, bang bang controls. When I step on the foot pedal, mine does the same. I think that the idea is that when you need a function, you have to step on the pedal anyway, so why rev up when you're not moving? The electric actuator moving a cable to the throttle is what makes mine increase in rpm. So, maybe start by seeing if the linkage got tighter, or cable kinked, or rusted up. Sounds like it might be revving too much, which is an adjustment......but why did it change? Or, is the command to have high throttle stuck on all the time? Mine has no computer, just switches and relays, so it's possible to troubleshoot stuff like this, especially if the fault isn't intermittent. But, like I said, on mine, when HI engine speed switch is on, it revs up when you push the pedal, even if you're not actuating any controls.
Hi there
I have 1989 JLG 40H that was running normal then suddenly the RPM went to maximum high. I shut if off with the master switch and the engine rattled and died. Moments later I restarted it and RPM went super high again. After that I can’t restart the engine anymore and ignition coil has no spark. Does anyone know if it’s caused by electric governor or electric spark controller or is it something else malfunctioning. I would appreciate some feedback. Thank you
I have 1989 JLG 40H that was running normal then suddenly the RPM went to maximum high. I shut if off with the master switch and the engine rattled and died. Moments later I restarted it and RPM went super high again. After that I can’t restart the engine anymore and ignition coil has no spark. Does anyone know if it’s caused by electric governor or electric spark controller or is it something else malfunctioning. I would appreciate some feedback. Thank you
Topher247
New Member
This is a great thread! Thanks for all the good info here. I'm having a lot of the same problems with my JLG as well!