This generator has 960 hours on it and it decided to gain personality and start cutting itself off after 10 minutes of running just fine. I have taken it in and had new starter, fuel pump and it starts fine ....runs fine for 10 minutes and then just shuts off any ideas before I return it to the mechanic??? Thanks for any ideas!

Gas? Model? I've had some problems with the auto-choke, making it run rough when the choke decides to close up, but it doesn't kill it.

Easy things first:

How is the oil level?

How is the fuel filter?

How does it do with the hatch open?

Do you know if it is running out of fuel or spark?

I am 9 or 10 years away from working on an Onan, but here is some general stuff:

I would install an inline spark checker in the ignition lead and connect a test lamp to the + term of the coil and sit down in a lawn chair with a cold one for 10 minutes.

Are both testers lit at shutdown? This gets a little tricky to watch, as the spark stops when the engine stops. And the coil +12 volts goes away when the oil pressure drops, but clever observation will often tell you something.

What happens when you jump from hot to the coil? This bypasses low oil and overheat sensors as well as some relays that can be crabby.

As for fuel, check the fuel with a pressure gage teed into the line. (Most vacuum gages can act as a fuel pressure gage). The clear glass fuel filters make trouble-shooting easier, sometimes, too.

It might be easier to positively eliminate the coach fuel supply by running a hose from the pump inlet to a can of fuel, so it is sucking up good fuel through a good line..

What does the electric fuel pump sound like right after failure? If it sounds fast or rappy, it could be air in the lines.

Does it hunt or smoke before it fails? Or is it just sudden?

Does a load make any difference?

I have seen a number of gensets shape up after a dose of Red Line Fuel System Cleaner.

The fact that it quits somewhere around the time the choke opens fully makes me think there might be a carb problem. It could run OK on the richer choked mixture, but quit when it no longer had the richer mixture the choke provided. Crud or a low float level could do that. So could a restricted fuel inlet. If a cracked fuel line is letting the genset suck air, the same could apply. Again, a clear filter can help by showing air in the line.

Does it have a degasser solenoid valve?

Does the genset have a really good clean ground?

Are all the wiring connections clean and tight? Some connections can get loose as they heat up.

Are there any exhaust leaks blowing hot air into the gen bay?

How does it work with the spark arrestor removed?

How does it work with the muffler removed?

Sometimes a condenser will fail when it gets hot, as will a coil.

Points and gap OK?

How long before you can restart?

Where is the electric fuel pump located? If it is inside the genset compartment, it can get crabby on hot days. Running with the door open will help isolate heat-related problems.

What happens when you disconnect the dashboard switch and its wiring?

quote:

Originally posted by Danny Z:
Gas? Model?

Sorry about that... it is a gas model Onan 6500 It is a sudden stop. I tried the fuel hose to a bottle of gas seemed fine. I have run it "with a load" and without. Oil was just changed and it does not smoke at all. Gonna experiment some more tomorrow. and check the other things

Had a problem with my Onan a few months ago. Would start and run for a few minutes then quit. Did all the usual checks, filter, fuel supply, fuel pump. Then it occurred to me. I had too much oil in it and after a while, the oil would foul the plugs and it would quit. Drained the necessary oil out and the thing ran fine. Have no idea how the extra oil got in it

quote:

Originally posted by Gorman Newman:
I tried the fuel hose to a bottle of gas seemed fine.

Am I correct in understanding that it works fine when sucking gas from a bottle? If so, that would point to a bad fuel line or pickup problem on the coach.

I had a bad fuel line on a previous coach, and didn't have the time to fix it for a while, so I ran a hose from the genset fuel pump down into the filler neck whenever we needed the genset.

quote:

Originally posted by bill h:
If so, that would point to a bad fuel line or pickup problem on the coach.

If you have less then 1/3 of a tank, you might be running out of fuel...

Fill the fuel tank and check again.

The pickup tube for the generator is mounted much higher then the engine pickup tube is.

You probably know that the generator fuel suction tube is higher in the coach fuel tank than the engine tube. If your fuel tank is less than 1/4 tank the generator may not run because it is sucking air rather than dino juice.

The generator engine will shut it's self off if the oil pressure is not adequate, but this does not explain why it runs ok when operated out of a separate fuel container...
Oil does thin after it warms up resulting in lower oil pressure. The lower pressure may not be enough to keep the pressure switch "made" resulting in it turning off. This could be trouble shot using an indicator lamp on the sensor to see if power is passing through the switch during normal operation. Jim’s explanation above describes this well, oil will foam if over-filled. Foamed oil does not produce pressure…just bubbles.

Both start and stop switches are momentary. The oil pressure switch is an integral part of the generators operation since it is used to secure the generator. By this I mean that when the "shut-down" switch is made, ignition power is interrupted until the engine coast to a stop or until the oil pressure switch no longer senses pressure. The opposite is true when the "start" switch is made. The start switch bypasses the oil pressure switch, forcing electrical power to the electric fuel pump, ignition and start motor simultaneously. When the generator cranks up to speed oil pressure is sensed and the engine is allowed to run. This can be characterized by a engine that runs when you hold the start switch and immediately turns off when the switch is released even though it seemed to be running fine.….if this is case there is a problem with the oil pressure or associated circuitry.

A friend has a 6.5 Onan went through the 15 minutes of heaven followed by hours of hell until he changed out all the safety switches.
This was a 1984 model marinized but as I remember there was an oil pressure switch, head? temp switch maybe one other. I don't think these were very expensive even though they said boat, aka bring out another thousand. As I remember these look like snap disc switches.
Good luck

Thanks guys for the suggestions....I get to try these and see if I can conquer this... if not I at least have some suggestions for the mechanic who just tuned it up.