The Onan generator in our 2003 Class C motor home randomly stops. It is an Onan Microlite 4000 Spec K. Model 4KYFA26100K.
It will run anywhere from 5 to 30 minutes when either loaded or no load. It always gives a 36 fault code which is, genset stopped without fault condition.
I first checked out the fuel supply with a gauge and it stayed at 3.5 psi even when it stalled and that is in the ball park.
I then discovered that when it stalls it loses spark and will not restart until it has set awhile. This is to probably to cool off and then the spark will return. It will then run perfectly again until the next stall.
I downloaded a service manual and that helps a lot. Here is the manual that I used.
http://www.cumminsonan.com/www/pdf/manuals/981-0530C.pdf
It looks like the problem could be either the control board or the ignition coil which I have also seen called the electronic magneto. My reading of the secondary winding between the spark plug wire and ground is 17,750 ohms. The manual says to replace if it is not between 12,000 to 23,900 ohms, so that side looks ok. I cannnot find a test reading for the primary side, but checking right after it stalled showed an open between that terminal and ground. After it cooled down it still only reads 1.5 M ohms and the unit will run so evidently that side is not able to be checked properly. The wire from the primary side of the coil goes to terminal 15 on the control board and is labeled ignition kill.
At this link is a picture of the coil. http://www.partsfortechs.com/asapcart/1660866-ignition-coil-onan-ky-spec-j-after-p-380.html
In order to even see this coil I had to drop the generator out of the motor home, remove the start solenoid and control board, loosen six generator mounting bolts so that I could raise the flywheel end to remove the outer housing.
The ignition coil air gap should be from .009 to .015 inch. This one had .004 clearance. I removed it and cleaned everything up and set the air gap at .012 inch. After the generator randomly stopped I felt of the ignition coil and it was not even warm.
I would be willing to order a new coil but am wondering if anyone has a method to check the old one out. I have already purchased and tried the expensive main control board and have had the same stalling results. At the local RV shop where I purchased the control board they said that the problem is almost always the board and they have no way to check out the old board except by substitution. They said that the voltage regulator is also located in the control board on this model.
The stator winding resistances all check out ok and when running the voltage and frequency is ok and stable.
Does anyone have any good ideas on this repair? The RV shop said that it would be two weeks until they could get at it if I brought the motor home in but could be sooner if I just brought the generator in. But it will be $85 an hour and these things aren't the easiest things to work on.
