Onan generator runs with no fuel pump?!?

[KyleR]

I’ve had intermittent issues with our Onan 10KW generator model MDKWB (diesel) tripping the DC control circuit breaker (the 10amp red breaker) shortly after startup. Finally dug into it last weekend and this is what I discovered.

I traced it to a high current draw on startup and by process of elimination narrowed it down to the electric fuel pump. And during that process, after disconnecting the electrical leads to the fuel pump, I started the generator to monitor the current draw. I expected it to run briefly then shut off since the fuel pump was disconnected. Unexpectedly the generator ran great - and continued to run fine for 3+ hours. And I've probably added close to 10 more hours over the rest of the weeknd and today. All without the fuel pump connected electrically.

The only thing I can figure is that the fuel level in the tank is higher than the generator injectors and must have enough elevation head to ovecome all the flow restrictions, including a Racor filter and the non-working fuel pump. Does this sound right?

My real question is this: will running our generator without a working fuel pump cause any unforseen problems (short or long term) with the generator? I plan to replace the fuel pump when we get back to a marina but wanted to make sure I am not doing any damage like it is.

Thanks for any info!

Kyle

[bud37]

Are you sure that was not just a lift pump.....?

[KyleR]

It's just a regular low pressure electric fuel pump that supplies fuel to the injector pump. Here's some pics for clarification (they show up sideways). Thanks!!

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20230212_124642.jpg

[bud37]

Ok ...what I thought...probably needed cause they don't know how the install will be plumbed and for high load situations where more fuel is needed.......good find on your part.


Good info for others...

[KyleR]

Thanks! That's what I was thinking too - just a lucky suprise! I know those engines are designed to have excess fuel flow (due to these low pressure fuel pumps) and have a return line to send most of the fuel supply back to the tank. I just wanted to make sure there were no "unintended consequences" that I was overlooking. Thanks again for your reply!

[km1125]

I can't imagine a scenario where you could do any damage operating it like that, but you might run into one where you need that pump to get it running. This would include something that would get air into the system, like an air leak on a hose (but not large enough to leak fuel) or replacing components like a fuel filter.