Onan 4000 MicroQuiet Runs then surges and stops

Thermostatic choke linkage/system, perhaps?

Looking further into this - I think my nice new fuel pump (Onan part) does not pump after about 3-5 minutes. When I let the motor run until it stops and then manually press the Stop/Prime button - no fuel pump activity can be heard. Wait 5-10 minutes and it pumps just fine. Also, it pumps hard to fill the float bowl and then gets quieter as it stops moving the piston inside the pump.

Who make a pump for these that will live and continue to work? Temp on the pump only goes up a few degrees in 5 minutes run time - no way should it be seizing up due to heat.

Anyone else had this issue?

I haven't looked to verify this, but I'm pretty sure the Logic Board commands the Fuel Pump to run. So it could be a connection at the Board. If you want to send a private message with your email, I can send a soft copy of the service manual, and there are troubleshooting charts in it.

"36" is a kind of "It Quit, Beats Me Why" code, often associated with running out of gas. Are you sure your fuel line isn't perforated someplace? Remember, all but the last foot is under suction, not pressure, so it'll be air sucked in, not fuel dribbling out.

chrisdug wrote:
Looking further into this - I think my nice new fuel pump (Onan part) does not pump after about 3-5 minutes. When I let the motor run until it stops and then manually press the Stop/Prime button - no fuel pump activity can be heard. Wait 5-10 minutes and it pumps just fine. Also, it pumps hard to fill the float bowl and then gets quieter as it stops moving the piston inside the pump.

Who make a pump for these that will live and continue to work? Temp on the pump only goes up a few degrees in 5 minutes run time - no way should it be seizing up due to heat.

Anyone else had this issue?

We have the same model Onan and had the same symptoms. It would run for about 10 minutes then surge and shut down just like a lawn mower that runs out of fuel. No sound from the pump with the stop/prime button after the shut down. If I waited a for maybe 1/2 hour, the pump would again run and the Generator would start and run another 10 minutes and quit again. After replacing the pump it has run fine since - for over 300 hours.

j-d may be correct about a problem with the control board. If you can get to the wire that runs the pump there is a spade connector that connects it to a wire from the control board. Disconnect the spade connector and use a test lead with alligator clips at each end to connect the end of the wire from the pump to one end of the test lead and the other end of the test lead to the positive cable from the house battery. This bypasses the control board. If you do this right after the generator surges and shuts down you can verify whether the pump or the control board is the issue.

In the picture below, the single wire at the bottom right is the fuel pump wire. When I replaced my pump I pulled it up to make the spade connector accessible. Take apart the spade connector and connect the pump side of the connector to the large red cable at the bottom left using the test lead to see if the pump runs.

Thanks for the test suggestion - I will try that next weekend when I bring it home again.

Just wanted to follow up - pulled out the control board and solenoid so the fuel pump wiring was exposed. Ran the gen until it stopped and then checked voltage going to the fuel pump - 12.3v. Bad fuel pump. Replaced with an airtex unit and it has been running under load for about an hour now.

I had replaced the fuel pump previously with an off brand from Amazon. It only had about 10 hrs on it before it failed. I hope the Airtex is a better unit.

Thanks all for the input and help!
Doug

Great News! Thanks for the update - many forget to do that and leave us wondering.