4000 onan

I had the same problem with an Onan 4000 and it turned out to be the ignition coil. It was very frustrating to figure out because the code, I think it was code 36, said something like an uncommanded shut down.
The unit has to be removed from the motorhome and tore down a little to replace the coil. I finally did a SWAG on it, replaced the coil and it ran fine again.

This should guide you in replacing fuel filter.....


Onan Fuel Filter Change

thanks guys tomoro morning should be cooler ill work on it

Suggest you do this:

1. Let us know if you've been using or at least exercising this genset at least monthly. It takes shockingly little time for today's sorry gasoline to clog the tiny jets in the ONAN Micro series carburetors. (Adding stabilizer to the gas, every tankful, helps prevent a LOT of problems.)

2. Post Model and Spec Code. If it's a Micro, the Oil Sensor was discontinued pretty early in the Spec List. Not realizing that causes us to chase a gremlin that doesn't even exist.

3. Notify Moderator and ask to move this thread to Tech Issues. Better exposure to OP's who work on gensets.

The red cap protects the threaded end that goes into the Micro's Fuel Pump. Lower left, inboard (toward centerline of coach) corner of the genset.

Micro is a single cylinder air cooled unit. Runs 3600 RPM, faster than your lawnmower at full throttle. Like a little B&S mower engine, it's splash lubricated. This means that oil has to be Fresh and Full. I emphasize Full because a couple years ago we had a rash of seized engines in these Micro's. They aren't a "bad" little machine, but they don't play well with Neglect. That's in both Fuel and Oil.

Repair manuals are available on-line - should be able to find one for free with a little effort or someone on this forum might provide you with link. Providing the exact Onan model might help. (including spec code).

Could be fuel pump, fuel filter, oil sensor over even a tiny hole in generator fuel line.

Changing fuel filter or fuel pump can be easy or PIA depending on your particular generator model - you might consider ruling out defective oil sensor first - jumping the sensor with wire should tell you whether the sensor is an issue.

I just changed the filter in mine. It Looks like This
It's located where the fuel line enters the gen unit. Take the dust seal loose and it on the end of the fuel line.

It i usually right before the fuel pump.

Get a new fuel filter for the generator. It probably needs changed. If not, at least you know when it was changed.

How is the oil level in the generator? If it's low, that could be the problem.

Also, another member had a similar problem a couple weeks ago. It turned out the low oil sensor was bad. He disconnected the sensor and the generator operated normally.
The sensor was then replaced.

It's something worth trying.

Let us know when you solve the problem.

I havert been out of the house for a week except at night I think is going to be 90 tomorrow may try it tomorrow

Well it's 85 here if that helps