my 98 Deere 790elc went to idle on its own wile I was working shut it off when startin it sounds like pump is working engine if I try to use hydralicks it kills the engine
Welcome to HEF old digger . What’s the machine serial # ? Check all the fuses ,especially fuse #3 “Engine control unit motor “ , this 5amp fuse powers the EC motor relay and the hydraulic pump control relay.
I have checked all fuses all ok have relplacedthe two solenoids on the pump still acting the same
Have any of the 1 amp fuses been replaced with something of higher rating ? With key on, check if the LEDs on the EC and PVC controllers (behind the seat ) are flashing approximately once per second ?
the fuses are ok and controllers flash 1 per sec
You can check for service codes using the LED on the PVC behind the seat. See the link to an older thread below. Post #14 shows how to enable the self diagnostic which sets a light blinking sequence, (if there are any codes). HeavyEquipmentForums . . The PVC is the bottom controller and EC is the top controller. Ignore the light on the EC. if there are any codes ,the light on the PVC will blink in a pattern of long and or short sequence.
Is the engine speed still only at low idle ?
I can get about half throttle but if you try to cycle bucket it will kill engine you can tell pump is working hard even at a idle
I have ran this excavator for 25 years have had problem but nothing like this
Try the engine speed learning procedure , see screenshot below.
Did you try checking for service codes as I suggested in post # 6 ?
serial no. FF790elc010228 it will track fine without killing engine but every thing kills engine on the power buttons will not go to power range really working engine short across to terminals get three lights blinking
Make a short video of the three lights blinking sequence. You will need to upload the video to something like utube and then post the link here.
ordered a pump controller but will not arive for 1 week
Let us know how you make out
got the new controller worked great then half hour went back to same problem pump loaded up function kill motor
Unless you get lucky or want to fire the parts cannon at this, the only way youre going to troubleshoot will be to get out your multimeter and start checking voltages while the machine is running and loaded up. A bad pump angle sensor will load your hydraulics up, as will a bad differential pressure sensor on your valve bank. Ive seen the linkage inside the pump for the angle sensor fail too, which can cause a bad reading and liad your pumps up. Theoretically a failed displacement solenoid could cause it also. If i was there, id start by back probing the three wires at the angle sensor, since im lazy and its easy to get at. You should have 5v on one wire, ground on another, and a variable signal voltage on the third. Last 790e i came across had a broken wire right where it went into the angle sensor that was intermittently loading up the hydraulics. It was pretty easy to pick up on with my multimeter
And do what Diesel Dave suggested. Check your fuses and your flashing lights
I think maybe the new controllers is the problem it did work for half hour going to do parts cannon ordered another controller voltage to differential sensor is where its suppose to be dont have much hair left got to find soon or will start on pulling teeth
We found the problem yester day it was asolenoid on the pump it would work for half hour then get hot enough to make the pump shut down had a simular problem with dump tk years ago ran till solenoid got hot enough and it would shut down Thank you for all your help
I did get new solinoids for tha pump now i can dig but my tracking is real jerking
Check the controller ground wires for a solid connection. The grounds bundle is bolted to the cab floor at the operator seat pedestal.
did that they are clean changed the differanl pressure now no jerking but it goes to idle when it travels about 30 ft
Is auto idle on ?
park it for the winter