Onan Start prime switch

[Boerne RV]

5 or 6 years old with less than 100 hours. Started fine and ran all day a couple months ago Now it starts right up and runs as long as you hold the switch down.
There is a clunk noise when the switch is released and it dies.
Took it to Cummins this afternoon. Should know what the problem is tomorrow
If it had 3-5,000 hrs I would say it’s the brushes and take it apart myself.

[Luke D]

Originally Posted by Boerne RV

5 or 6 years old with less than 100 hours. Started fine and ran all day a couple months ago Now it starts right up and runs as long as you hold the switch down.

There is a clunk noise when the switch is released and it dies.

Took it to Cummins this afternoon. Should know what the problem is tomorrow

If it had 3-5,000 hrs I would say it’s the brushes and take it apart myself.

Wow... mine 363 or 364 hours. No clunk just dies. Will run forever if switch held. Keep me posted. Thanks

[pneumatics]

That is alot of work. One other item to check is the 120VAC output power wiring. The Genset has a circuit breaker which is for overloads. Only.
Check the wiring where the sealtite conduit comes into the genset and make sure all the connections are secure. This same sealtite goes to a junction box somewhere on most of these and then to the house (YMMV). check the connections there also.
Motorhome back I had the same problem where the factory did a poor job wiring the 120VAC at the junction box mounted on the frame and the wire nut on the hot was loose and eventually fell off. When bouncing down the road in the summer with the A/C on it hit the grounded box intermittently. Never at other times. Inside of the box was black so it was arcing but ran fine.
What it did was cause short sharp surges back to the genset, the Magnetic breaker on these will not trip under this type of short duration spike. It caused the excitation field brushes on the generator to foul and pit.
I found and repaired the junction box but the next year the genset did the same as yours and the code on that was no power. At that point, removed it and took to service and $1000 later had it like new. Carb, rebuild brushes and gen side, controller, pump.... At that point it was about 5 years old.
Good luck.

[Luke D]

Originally Posted by pneumatics

That is alot of work. One other item to check is the 120VAC output power wiring. The Genset has a circuit breaker which is for overloads. Only.

Check the wiring where the sealtite conduit comes into the genset and make sure all the connections are secure. This same sealtite goes to a junction box somewhere on most of these and then to the house (YMMV). check the connections there also.

Motorhome back I had the same problem where the factory did a poor job wiring the 120VAC at the junction box mounted on the frame and the wire nut on the hot was loose and eventually fell off. When bouncing down the road in the summer with the A/C on it hit the grounded box intermittently. Never at other times. Inside of the box was black so it was arcing but ran fine.

What it did was cause short sharp surges back to the genset, the Magnetic breaker on these will not trip under this type of short duration spike. It caused the excitation field brushes on the generator to foul and pit.

I found and repaired the junction box but the next year the genset did the same as yours and the code on that was no power. At that point, removed it and took to service and $1000 later had it like new. Carb, rebuild brushes and gen side, controller, pump.... At that point it was about 5 years old.

Good luck.

Thank you for the help. Their not pulling generator until May. Since it was out in November when last fixed I am going to go re check all connections. I check all inside but never the a/c an others you mentioned. I inspected all I could get to spots as the generator is in the Motorhome. I could not find any critter damage or traces. I pulled switch, control board an checked for loose wires or chewed there no luck. I suspected gen not producing power. Especially since it will run forever when you keep finger on start. Was running fine prior to this mess. It did surge a bit once and I found ground wire from fuel solenoid was loose at block. They stripped that torque, so I re tapped and fixed with a little bigger torque. Then ran great again. Your ideas are greatly appreciated. I’m as I said totally disappointed in the Onan 4000 micro quiet 4KYFA26100P model. In two years of ownership It’s ran less than I can mention. Had 310 hours on it so in 2 years I’ve got it to run 54 hours. 10 or 12 of those as every few weeks maintenance runs under load. Not to mention engine failed and was replaced under warranty last year also. At least my extended warranty has covered issues so far. I thought of checking slip rings but looks like removal necessary on this model. It sucks knowing it’s a power issue once switch released but WHY ??? Is not an easy answer yet.
Thanks
Luke