Motorhome AC Generator Problems
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Motorhome AC Generator Problems
A friend has a 2000 Ford Fleetwood motorhome on a 1999 35 foot chassis (S/N 3FCNF5356X5A31308). The problem being experienced is not with the motorhome itself but with the on board generator installed. The generator is a 1999 Onan 5500 Marquis with a 12v fuel pump. We’re not sure if the fuel system is pressurized or not, I’m assuming it is since the coach is V-10 power with fuel injection and we don’t know if the generator fuel pump is a diaphragm or impeller type.
The problem appears to be related to fuel pickup but it is very strange, the generator will not start and run from the on board fuel source (the motorhome fuel tank), but will start and run from an external source, also once started from the external source if the line is switched back to the main fuel tank it will continue to run, we allowed it to run for @ 1 hr on several occasions, every time the unit was turned off it refused to restart on the tank fuel.
When is does quit there is no fuel in the pickup line, bone dry.
We assume the fuel is fine as there are no issues with the performance of the coach itself, and the fuel level is above the ¼ minimum to power the generator.
The generator fuel line has been replaced with no effect.
All items installed are original with no aftermarket add-ons.
Fresh oil (31/2 quarts) and filter
The generator has 16-18 hours run time clocked and has always run fine.
When Onan was contacted about this problem they were either unable or unwilling to offer a solution, not a very knowledgeable technician, their only response was “bring it in and leave it we may look at it.”
Neither Fleetwood nor the local dealers responded with any more positive suggestions. Standing back and throwing money at it is not an acceptable solution. Any and all assistance is appreciated.
The problem appears to be related to fuel pickup but it is very strange, the generator will not start and run from the on board fuel source (the motorhome fuel tank), but will start and run from an external source, also once started from the external source if the line is switched back to the main fuel tank it will continue to run, we allowed it to run for @ 1 hr on several occasions, every time the unit was turned off it refused to restart on the tank fuel.
When is does quit there is no fuel in the pickup line, bone dry.
We assume the fuel is fine as there are no issues with the performance of the coach itself, and the fuel level is above the ¼ minimum to power the generator.
The generator fuel line has been replaced with no effect.
All items installed are original with no aftermarket add-ons.
Fresh oil (31/2 quarts) and filter
The generator has 16-18 hours run time clocked and has always run fine.
When Onan was contacted about this problem they were either unable or unwilling to offer a solution, not a very knowledgeable technician, their only response was “bring it in and leave it we may look at it.”
Neither Fleetwood nor the local dealers responded with any more positive suggestions. Standing back and throwing money at it is not an acceptable solution. Any and all assistance is appreciated.
Fleet Mechanic
Joined: Jul 2003
Posts: 1,570
Likes: 20
Onans have a bunch of problems operating on Ethanol. The fuel in the tank is probably above 10% ethanol. The gas can fuel below 10%, yes once its warmed up it will run on Ethanol, if the tank is full enough. You must have a very clean air filter for Ethanol. Also I doubt you have an electric fuel pump on your Onan. What you are seeing is the 12 volt Solenoid. It'll cut the Onan off on low oil pressure and may be tied into the CO/Smoke alarm in the motor home. The Carburator floats swell with Ethanol over a period of time and the fuel pump diagrahm can fail. Also ignition system may have to be upgraded, Onan P/n 160-11376 is the one I used. The generator will need to be resyncronized(sp). Use a plain 115VAC wall clock, with a second hand. Adjust syncro. using a stop watch till you get a perfect 60 seconds out of the clock timed to the stop watch. I used my GShock to time the clock. Look up Onan Ethanol problems on the net. I wouldn't use the local service that wasn't upfront with you on the problems. As they will probably just fix one thing, and then cha ching you on future repairs.
Fleet Mechanic
Joined: Jul 2003
Posts: 1,570
Likes: 20
I know this can be done, but I can't remember exactly how we did it. I know we took a half liter of Gasoline and added water to it by the milliiter, till droplets of water started to appear in the gasoline. Also can't remember if we were testing for Ethanol or Methanol.
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