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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14436
Experience:  Certified on Onan and Generac generators
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I have a onan 4000 kW. It will not start or run. It will run

Customer Question

I have a onan 4000 kW. It will not start or run. It will run with a small shot of starter fluid. Which leads me to believe that it is a fuel problem.I think I have traced it to 2 problems. First it has an after market fuel pump that says it's for a 4,6,8 cylinder motor. It may be the wrong pump. The second problem may be the control board. I'm only getting between 8.6-9.5 volts of the pin to the fuel pump.
Submitted: 2 months ago.
Category: Small Engine
Expert:  Hank F. replied 2 months ago.

Hello, my name is ***** ***** I am going to assist you with this.

You definitely have the wrong fuel pump on there.

But you still need to test it out.

Disconnect the fuel line from the carburetor, and run it into an empty container (you will need to attach a piece of rubber hose for the sets that have a steel fuel line).
Unplug the tan wire from the pump.
Jumper 12V directly to the pump.

If it is pumping gas like this, the pump is good.
If not, either the pump is bad, or the fuel line is bad.

Remove the fuel supply line from the pump, and attach a length of fuel hose to it.
Drop the other end of the hose into a gas can, and jump 12V to the pump again.
If it still does not pump, the pump is bad.
If it does pump, the fuel line is bad coming from the fuel tank – or you are low on gas.
There must be at least ¼ tank of fuel for the genset to run.

Let me know what you find.

Customer: replied 2 months ago.
I have ran the pump direct from 12 volt and it seems to run fine. So is the 8.6- 9.5 volt typical off the control panel pin typical? Running the pump off of the pin the pump runs slow.... So not enough power to pull has from the tank.
Expert:  Hank F. replied 2 months ago.

There is no minimum set voltage listed for this, but usually about 10.5V is about as low as you want to go.

But I have seen several run on 9V.

Customer: replied 2 months ago.
I'll check and if need be I'll replace the fuel pump. Do you have the correct part #for the pump. It may take me a day. But I'll let you know.
Expert:  Hank F. replied 2 months ago.

The current part number for that fuel pump is A029F891.