Hey guys new member here. 1993 JD 490e won’t throttle up No voltage down at the EC motor plug. Fuses good relays good EC motor replaced along with sensor I think it’s the “switch box” controller in the cab but not certain. Wanna test controller and guarantee it’s my fault before ordering another. Any help is appreciated thanks a lot! Liam.
Doesn’t that machine have a mechanical injection pump on it.?? This might sound silly but, have u disconnected the throttle linkage and ran the engine, controlling the rpm’s with the throttle on the pump ? (U haven’t mentioned any diagnostic testing)
Welcome to HEF WestCoastWrench ! First, make sure you do not plug and unplug the EC motor with the key on. That will ruin the controller. Do the I, L, E and P lights work as you try and change engine speed? Does the EC motor make any kind of noise when trying to change engine speed? How did you check voltage at the EC motor? Plugged in and backprobed, or unplugged? If all your fuses are good and relay K12 is passing voltage on, is that voltage reaching the engine controller? Does the engine controller have good power and grounds?
Haven’t disconnected throttle cable yet but the owner of machine has been running it via buggy cord at throttle since this problem arose a while back. So the engine does throttle up and run fine, just no response out of the EC motor. The lights all come on as you select different power levels in he cab but no results down to EC motor
I tested for power with the hardness unplugged at the EC motor, Then tried back probing with no changes. Haven’t plugged/unplugged while key on. EC motor is not making noise. The EC has its red “heart beat” light blinking. I don’t have any schematics to go through as for which pins are what inside the harness.
Check your PM's. You will need to check that the voltage from the relay is reaching the engine controller. Also, you will need to verify power and grounds to the engine controller. You should also be able to see if the I, E, L and P signals are reaching the engine controller as well. They probably are since the lights work. I don't recall if they are a power signal or a ground signal.