I have a customers generator that the rpm was running away. Unit would continually hunt, with rpms going from just above idle to way above 3600.
I disconnected the stepper motor and could make the engine rpm steady, to the point where the controller wasn't faulting out on overvoltage.
The stepper motor resistance readings were all approx 11.6 ohms, although I could feel a distinct bad spot in the stepper arm travel when manually moved.
I installed a new stepper motor and the RPM hunting stopped. The issue now is the rpm's are way too high (90+Htz) but constant.
The output voltage was 240, so the ARV is working. Unit will run for 10 to 15 seconds before shutting down with a fault of [RPM sense loss].
I'm suspecting a bad controller, but feel I should be checking where the controller gets it's rpm sensing. I'm, at a loss as to what exactly test to determine if controller has what it is supposed to see.
The unit starts fine, will hunt for 2 to 3 seconds at a lower rpm then goes right to "very high rpm's" and stays there until the controller faults.
While it's running at the very high rpm, I can read 240v at the generator side in the main circuit breaker.
I'm mostly looking for anything else I should be checking before I order a new controller.
Generator model- 0059201 S/N 6902698 Controller- Nexus 0H6680D
Here's an update on the troubleshooting. After determining the controller gets its rpm sensing by counting ignition pulses, I went back and checked a few more things.
I installed two spark plug glow testers so I could see the spark. When i started the unit, rpm went to real high and stayed there, then controller faulted. I removed the stepper motor cam and restarted. I could control the rpm manually and it would run just fine for as long as I wanted, both spark plugs happily firing away.This would seem to prove the controller sees the pulses.
I reconnected the stepper motor and restarted the unit, everything worked perfectly, ran it for 20 minutes, no problems, Both voltage and rpm's were fine.
Shut down unit for ten minutes and restarted, right back to high rpm. I did notice that when the controller faults, around 4200 rpm, the far spark plug stops sparking, but the near plug sparks all the way down to 0 rpm? If I turn the unit off before it faults, both plugs spark all the way down to 0 rpm.
Is it possible that wire 18 is compromised somewhat and making intermittent contact, or is the controller bad and not making the conversion from pulses to rpm.
Thanks for your time