91' Onan 8KW Gen trips 15 amp DC Control Breaker

Ok... DREW E. well here I am in April but the situation has been identified finally after a couple of months of not having a Generator and fretting over the replacement cost and Chassis retrofit for a newer Model. As it turns out after replacing everything possible that could blow a fuse in the Control Box ( namely, Temp sensor switch, Oil sensor switch, Fuel Solenoid, Fuel Pump, Control Board ouch 400.00 just for that but at least I got a spare :), I mean I went back to Cummins here in Miami at least 6 times for "the" part that I knew would solve the problem. It got to the point where the Cummins Parts Sales guy said why don't you just give up and bring it in Man!. Of course I couldn't do that because they at 100.00 bucks an hour would have certainly put me in the Poor House trying to figure this one out. As it turns out the problem was a "Crumby" 12v lead off the Fuel Solenoid back to the Fan! But I did not know where that particular lead went to at first. So by sheer Dumb Luck out of Frustration I happen to try disconnecting some leads, then starting and re-starting over and over... That particular lead has a 20 Amp in-line fuse attached (must have checked that fuse 100X),,,,I hit the start switch and to my amazement the Genny kept running!. Scratched my head, Shut her down again reconnected the lead and tried again and the fuel solenoid disengages and she shuts down! So hoping that lead meant nothing to the Genny operation...lol.. I left the lead disconnected to run the Genny and she ran perfectly while I'm underway. But first time I stopped for a longer period she began to overheat. That's how I discovered it was the lead for the electric cooling fan that sits in front of the Radiator! The electrical wiring diagram for the generator doesn't even show a Fan lead! The Fan works fine albeit when the lead is connected. So now I simply remove the lead to the Fan in order to start the Genny and then reconnect after starting so the Fan runs! Apparently the electrical draw of the Fan upon start-up was enough to trip that DC Breaker in the Control Box! I HOPE THIS SAVES SOMEONE ALOT OF TIME , ENERGY AND MONEY... AND I MEAN ALOT OF TROUBLESHOOTING ON A PROBLEM THAT EVEN STUMPED THE GENSET EXPERTS HERE IN FL. AS WELL! CAME DOWN TO INSANE FRUSTRATION WHERE I JUST STARTED PULLING WIRES OFF AND STARTING AND RE-STARTING OVER AND OVER... LOL.

I have had many pumps fail after a long life. Direct short. Also if your model has the twist lock plug on the side of the control box. Make sure it is making good contact.

Finally had a chance to get back to this problem. Process of elimination here but finally think I found the problem after diagnosis of the 12 v Fuel pump. Passes a continuity test when isolating the Control Box circuit from the pump but fails when connected back to the pump. Also appears that no fuel is being pumped. Well the assumption....only and assumption because who knows what else may be lurking in this Oldie but goodie 8KW is the pump is failing or sending a dead short back to the Control relay tripping the DC breaker which in turn disengages the Fuel Solenoid causing it to shut down after running a few seconds. Pump will be ordered here through Cummins South Miami tomorrow will update after the install.

Reply Thank You Drew E. going to try and order a harness today from Onan. I'm also trying to nail it down a bit and rule out the possibility of any of the two sensors (oil and temp) that would make that DC 15A Breaker blow. Wouldn't want to replace those if they don't have anything to do with the DC Breaker. Again the manual states those sensors would trip the circular small fault Breaker but doesn't say anything about the DC 15A breaker blowing. Perhaps the harness would most likely be affecting that. Basically trying to figure out what component(s) ( e.g. , voltage regulator, etc. ) that breaker specifically handles rather than start replacing things that have no effect on it. Going to see if I can dig a wiring schematic out of the manual today. Thank You!

Could be lots of things I suspect, and I'm far, far from an expert on generators. However, it does occur to me that a questionable wiring harness could be sporadically shorting out due to vibration when the generator runs. Especially since the harness is going to need some TLC sooner or later, I would probably bite the bullet and refurbish it properly and see if that cures the problem.