Onan fuel pump or carb

[Apollo11sailor]

My Onan 4000 model KY L with 170 hours will start and run for a couple of minutes then it dies. Acts likes it is running out of gas.

Knowing that the fuel tank was full I suspected the fuel pump. I disconnected the fuel input line from the filter and connected a short hose that I inserted into a gas container. Then pressed the Stop button to prime, worked fine. Next pressed the start switch and the unit started and ran fine for three or four minutes till I shut it down. Thinking that this confirmed that the pump was OK I put everything back together and restarted the unit. After about two minutes the unit started to sputter or surge. Did that for about 30 seconds and then died. I immediately disconnected the carb input goes and there was no fuel evident.

Is it possible that the pump has degraded and can no longer sufficiently pump fuel from the tank. It seemed to work fine when I tested direct from a container from about two feet.

[64thunderbolt]

I just replaced mine with an automotive type pump. Bypassed the oem pump. It is a low 5/7 psi for a carb. No need to prime any more just hit the start and it is off & running. Could be the carb also. Take a piece of fuel line & connect to pump then put other end in a can of seafoam. Run it till it quits. Replace orig fuel line and see what it does. These carbs gum up easily.

[ThomasFour]

For integrity of the topic, I would refer back to Harley-Dave's post. Part of the issue - which I also had - was the pump would overheat and stop pumping fuel. You could hear the engine starving for gas and the line was dry. Just doing what RJsFishin described may not replicate the problem sufficiently to provide accurate diagnosis. My pump would function for 4-6 minutes before overheating and engine quitting. There may also be some effect of having the engine running (ie., creating heat) as opposed to just priming for 2 mins in the scenario he suggested. Good ideas RJsFishing, but I am just throwing some more info out there.

[Apollo11sailor]

RJsfishin, thanks much. That is essentially what I ended up doing, just in a different order. I have ordered the pump and filter. Expect to be back up tomorrow.

Thanks to everyone for your inputs.

[RJsfishin]

I'd trouble shoot it differently
Disconnect the fuel line at the carb,... have 2 minute container
Hit the prime button, plenty of fuel ? Its the carb. No fuel ? Its either the pump or the line to the tank.
Disconnect line to pump inlet, add a hose to reach the ground
Hit prime w/ container of gas on the ground. NO gas ? Its the pump. Gas ? Its the line to the tank, either sucking air, or blocked.
Simple as that !

[Apollo11sailor]

Thanks for the input.

[j-d]

Well,

StaBil and exercise reduce chances it's the carburetor

You found the fuel line dry when the generator quit

Others have had the same condition and it was fuel pump

Fuel pump is less expensive than carburetor

Seems to me you have a good chance of fixing it by throwing a pump at it.

I think I'd go aftermarket. Partly because one of those aftermarkets might be ONAN's supplier. Partly because ONAN could be having them made offshore just like the aftermarkets.

You need a T30 TORX bit to do much of anything on an ONAN 4KY.

[Apollo11sailor]

I did get an initial code of three blinks but I inadvertently canceled it rather than expanded it. My unit is a 2011 and I am the second owner. I have excercised the unit on a regular basis and do use stabil. I did check the line all the way back to the tank and found no problems.

[Apollo11sailor]

Thanks for the replies. Did you replace with and OEM pump or aftermarket?

[harley-dave]

yep, fuel pump was our problem also. Pump will warm up and stop working until it cools slightly. Then works again. Would surge just a little moments before it would die.

Dave

[ThomasFour]

Had the exact same thing....fuel pump replacement fixed it. If you search this topic, someone else was reporting the same issue a month or two ago. Never bothered to see if that person reported their success/fix, but I also suggested fuel pump to them. My troubleshoot was to take off the fuel line and indeed the line was dry when the motor stopped. That's how I decided to go with a new fuel pump and it fixed the issue. No problems since.

[j-d]

Apollo11sailor wrote:
My Onan 4000 model KY L with 170 hours...

Is it possible that the pump has degraded and can no longer sufficiently pump fuel from the tank?

Spec L and 170 hours...How Old? Still Warranty? Have you been using it regularly or at least giving it a monthly exercise?

What Trouble Code is blinking on your Start/Stop switch or Control Panel?

If it's young with low hours, pump failure isn't likely. Still any part can fail prematurely. But... If the coach stands without genset use, especially without stabilized gas, carb trouble can develop within a couple months.

We had a gunked up carburetor. I could start it and it'd run under load till the load came off. Example, would carry air conditioner compressor (heavy load) till it cycled off, leaving only air conditioner fan (light load). Then it'd quit. The idle passages were clogged. Don't forget, the genset runs at a steady 3600-RPM, BUT! at light or no load, the small idle passages come into play even if it's still running 3600. Apply a load and it's still running 3600 but on larger passages that don't clog as easily.

The gas tank is full. OK, now can you check to make sure you don't have a loose clamp or pinhole leak spot?