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I have a 790e lc deere excavator the auto idle isn't working…

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Hi i have a...

Hi i have a 790e lc john deere excavator the auto idle isn't working the p for the max. power mode switch light is on and will not go off if i press i,l,e mode switch i pulled on the throttle to speed up the machine but when i try to use it the engine losses power bad i checked the fuses all are good can you tell me what might be my problem are where to look also it will not speed up if you press the accelerator switch

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Submitted: 3 months ago.Category: Construction and Road Equipment
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Answered in 55 minutes by:
3/26/2018
Mechanic: Dan, Technician replied 3 months ago
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 6,791
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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Hi ,My name is Dan. I will be glad to help. We can follow up as needed on here, Give me some time to review your information and post my responses. Im not an employee of the site but I help on here as time allows in between jobs. Response time will vary depending on my work load , etc. What is the machine serial number?

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Customer reply replied 3 months ago
FF790EL0104977
Mechanic: Dan, Technician replied 3 months ago
First you were going to want to check all your fuses for power on both sides with the key switch on and replace any fuses with power only on one side. Check on your relays one at a time by swapping them with a known good one for testing purposes. If okay you want to check the throttle step motor that controls the injection pump position when moving the throttle control and make sure it reaches full throttle stop and idle stop in each of those positions. Also make sure that it is smooth and there are no open circuit between idle and full throttle. You can also test for voltage increase and decrease with a voltmeter as well to the stepper motor or throttle actuator in other terms.... If that works properly you will want to be sure that the console switches are working to select the modes and if the switches test good and the wiring test good then you could have a problem at the controller which behind the sea there is a machine pump controller and there is an engine controller on top of each other behind the operators seat under the panels. These will also get engine speed signal from the engine speed sensor and use that information for auto Idle. Check for those things and let me know the results and if we need to dig deeper into this. Please remember to take a moment and write my answers as that is how the site credits my time helping on the site. Five-star ratings and bonuses are greatly appreciated
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Customer reply replied 3 months ago
hi i checked the fuses already i have to check the relays next for the throttle control positions it is stuck on p and will not change but the engine doesn't speed to full throttle i will check the other steps you recommended i will let you know thanks
Mechanic: Dan, Technician replied 3 months ago
Thanks for the update. Yes check the other things and let me know. See if the voltage signal to the throttle Motor or stepper motor is changing when you select the different modes because if not the controller may not be getting we proper input signal 2 send that output to the step motor to change it. Pleasure to help.
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Customer reply replied 3 months ago
i checked the fuses, relays, all good i am not getting any current to the ec motor how do you open the console switch panel to check to see if it is working properly the console light is stuck on p it will not change for the throttle the auto idle light goes off and on when the button is pushed
Mechanic: Dan, Technician replied 3 months ago
Thanks for the update. This is where it gets more complicated. Even at the dealership this part of it is where it gets harder to diagnose and isolate. What you need is the electrical schematics for that circuit and the console panel. You will need to identify what are the inputs and output wires to that panel because as far as the panel itself Komatsu does not supply anything for its internal diagrams as they sell it as an assembly. So if you had the schematic to identify which terminals to test for continuity of that switch then you would use your test meter to test at the connector pins from the panel. If the wiring harness test good with no damage but if the switch is sticking on that one power mode it is likely a worn-out switch in the monitor which is replaced as an assembly.
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Customer reply replied 3 months ago
good morning i checked the wires all look good i checked the throttle motor 2 set of wires one set has all grounds the other wire set has no power i did notice when i first turn the key on the I button for the throttle mode lights up for a sec. or two then the p light comes on but it will not speed up and the hydraulic pump is binding and stopping the motor
Mechanic: Dan, Technician replied 3 months ago
Thanks for the update. If the hydraulic pump is lugging the engine down pull the hydraulic filters and inspect them internally for fine metal that would confirm a pump failure or component failure occurring. If found the whole system has to be thoroughly cleaned out before running any new replacement component.
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Customer reply replied 3 months ago
oil is good filters are good on a 790e what controls the pump pressure and the throttle mode its like something isn't regulating the pump if i manually speed up the engine it will work for a turn or two then it wants to died down when i use the controls
Customer reply replied 3 months ago
good morning where is the sensor located i see a sensor that looks like it on the side of the hydrauilic pump on the right side
Mechanic: Dan, Technician replied 3 months ago
that sounds like the one
... Try unplugging the wiring to it and see how the functions react
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