Onan generator dies like its out of fuel then runs fine?

[Garythelegend]

Hi I have an Onan marquis gold 5500 generator in my trailer. I had it out a month ago at 5500ft elevation. I was running it and it choked out and died like it ran out of fuel. Got home, 5250 ft elevation, gased up and it ran fine. I took it out this weekend camping at 8570ft elevation and it choked and died like it was out of fuel, I got under and looked and had over 1/3 a tank left. I started it up a while later and it ran for 15-20 minutes and died the same way. We came home and for kicks I fired it up and it ran for over an hour just fine so I shut it off. Any suggestions as to why it is doing this to me ??? 😞

[Sam_Spade]

Garythelegend wrote:
Awesome, thanks for the help guys! I think I will get a cap and see if that works if not I will spend some money and get a pump and sensor. I really appreciate the help!

And after you do all of that, you likely will have spent MORE money that you would on a trip to a Cummins/Onan shop for a real diagnosis and fix......and it still might not be fixed.

[Garythelegend]

Awesome, thanks for the help guys! I think I will get a cap and see if that works if not I will spend some money and get a pump and sensor. I really appreciate the help!

[htwheelz67]

Try loosening the fuel tank cap or removing it and see if it does it, I ended up replacing a fuel pump in the desert and it turned out to be the fuel cap vent......but I do have a much quieter fuel pump now. I have the same generator.

[alanmikkelsen]

My LP Onan was doing the same thing, I replaced the LP regulator valve and all is well.

[HackerAce]

I had the exact same problem and replacing the oil pressure sensor fixed it right upl

[FULLTIMEWANABE]

I'm not very techy and know diddly squat about mechanical things, but I recall when we gave ours a huge service at home, filters, fluids etc, I think I read somewhere in the manual that you have a setting on it for different elevations you should change. Just mentioning and might be worth checking in your manual for operating at high elevations versus sea level etc.

?Carburator adjustment at high altitudes?????? Just mentioning FWIW.

[CloudDriver]

Ours is a different model Onan, but we had the same symptoms. A new fuel pump fixed the problem.

[Garythelegend]

Oil is fine, I'll try the fuel filter

[Sam_Spade]

Let's see......if the tank vent (probably located in the cap) was plugged up, would it develop a vacuum in the tank quicker at a higher elevation ?? Maybe.

[gbopp]

Welcome to the forum.

Did you check the oil level in the generator? If the level is good, maybe the low oil sensor is bad.

When was the last time you changed the generator fuel filter?