S85 Will NOT drive fast at HIGH RPM but will on LOW RPM

[geniealwaysbroken]

Hello,

TLDR:
High RPM, Low Torque: Machine will not drive fast
Low RPM, Low Torque: Machine will drive fast
Ruled out Lim switches with 95% confidence
Found pinched ground running through the boom, potential harness pinch too?

Working on a 2012 Genie S85 4x4 serial S8512-9124. Having a weird issue where the machine will drive low torque(High speed) with the engine RPM on the low setting. but as soon as I switch the RPM to high the machine will not drive low torque. While driving low rpm high speed, I can switch rpm to high on the fly and the machine will slowly come to low speed as if it was in high torque mode. Super weird that it will drive fast if the rpm is low.

I checked to make sure the RPM was set properly in both high and low. Found one bad ground wire running through the boom, looks like it got pinched so it is possible the boom harness was also pinched?

I dont believe it is related to the lim switches or else it would not drive fast in low rpm. The service manual doesnt list any troubleshooting trees or guides (thanks terex) and getting ahold of service on 10yr+ old machines is not as easy as it used to be, post pandemic.

Tried locating the 2-speed valve on the traction manifold but it doesnt appear to be listed on the 4x4 manifold breakdown but it does on the 2wd manifold in the service manual (4x4 manifold isnt listed in service manual either but is in the parts manual?).

 

[DemiGod]

I am having the exact same problem on a S-60. Does yours go fast for a moment when traveling, when you switch from low to high idle?

 

[geniealwaysbroken]

Hey I got it fixed this morning, check pin 41 inside the ground control box, put your multimeter to the Hz setting and make sure the high idle isnt set too low or too high, the service manual will have the rating for high and low idle Hz depending on the motor type you have. This is just one way to check idle, mine was set too high and was probably triggering a dump valve or something due to higher than normal systems pressure? not entirely sure but its fixed now. Let me know what you find.

 

[DemiGod]

Sweet appreciate it. Let you know what I figure out.

 

[DemiGod]

Definitely didn’t fix up my problem? I have been through this entire machine and can’t for the life of me figure this out. All started just changing out the alternator as I was getting no tach signal. Didn’t see engine speed so it would shut down.

 

[geniealwaysbroken]

and you're getting tach signal now? I know I said check pin 41, thats for units with the little black Ignition Control Module inside the ground control box, your unit may be different. You could also verify high rpm with a physical tachometer and make sure its within 50rpm of factory spec. Could look at the 2speed valve on your traction manifold, make sure it's getting power to switch to high flow for rabbit speed and make sure the valve isnt being blocked. All it takes it one little metal chunk to block a valve. Could also try recalibrating your drive joystick just so cover all basis. You've looked at the primary angle cutout switch and the extension cutout switch?

 

[DemiGod]

So this is what I have done, we have 16 of these machines. So I am able to swap parts from other machines to trouble shoot. I swapped out the traction control box. The drive pump, the black box you speak of. Recalibrated joysticks, even did the threshold calibration. Man I’m at a loss, had to get away from that machine a moment luckily I have many machines to work on. Let me ask you this cause I’ve been mulling it through my mind. Replaced the alternator and went with a larger pulley and lengthened the belt by around 2”. Do you think the difference in that pulley could be my problem?

 

[DemiGod]

And no you was spot on on pin 41, turns out to be terminal 2 on said ECU. Dang thing has got me baffled.

 

[DemiGod]

Yes I have ruled out boom stow. It’s just so weird how it wants to go rabbit at low idle then hit rabbit it goes like a raped ape for about 5 seconds then slow again. So I know function is there something is kicking me out. I need to test the diode in the control panel on basket side. This is our only unit with a Perkins in it. All our others are Duetz in them

 

[geniealwaysbroken]

Wow I can imagine your frustration.

I believe so, technically by increasing the size you’re changing the gear ratio. I believe by increasing the diameter of the pulley the alternator you’re reducing the Hz frequency on its output. If its a perkins the Hz on high idle should be around 467Hz on pin 41 should be the 5-6th~ pin down from the top of the terminal strip in the base controls, definitely just double check the service manual. The Hz frequency should be losted with engine rpm specs, I think that extra 2 inches may be your problem, thats the only time im ever gunna say an extra 2 inches is a bad thing lmfao. Lemme know what you find.

 

[geniealwaysbroken]

Also to answer your original question yeah mine had the exact same symptoms

 

[geniealwaysbroken]

Yes I have ruled out boom stow. It’s just so weird how it wants to go rabbit at low idle then hit rabbit it goes like a raped ape for about 5 seconds then slow again. So I know function is there something is kicking me out. I need to test the diode in the control panel on basket side. This is our only unit with a Perkins in it. All our others are Duetz in them

Did you end up solving it?