Onan genset stops running--------Fixed

[427435]

Finally got the MH out. The genset started up OK and I let it run while I did some other things with the MH. It started to surge after 10-15 minutes and quit. It restarted after setting for a while. That cycle continued several times this afternoon.

My best guess is a mouse nest causing the overheat temp sensor to kick out. I won't have time to deal with it for a couple of weeks, but I'm interested in other possibilities to check before I pull the shrouds (which looks like it requires pulling the genset out). 😞

[udidwht]

Those who've claimed split fuel lines as the issue likely didn't have split fuel lines. Why? A split fuel line will always leak fuel and should be very obvious to the naked eye.

[roam1]

BobR wrote:
Start by dis-connecting generator fuel line. Mix a gallon of gas with SeaFoam and run generator for 15 minutes from gas can fuel(Have can higher than Genny for gravity feed). Let sit for at least 30 minutes and then restart. It just may be a gunked up carb. Repeat again if necessary. Might have to reset choke. If that doesn't work, then look at other culprits like fuel pump and filter.

what do you mean or how do you reset choke?

I ask because I had similar problem as the OP, same solution, but my choke has not worked since. It starts fine, runs rough for a few minures, then runs fine.
sounds to me like faulty choke

[427435]

booty51 wrote:
So old age and 80,000 miles causes the the crud and tar to ooze out of the fuel pump?

That's the most likely cause. Fuel pumps have been failing since they were invented.

[cbr46]

mcal63775 wrote:
My Onan 7000 Marqui experienced same problem. AFTER a new fuel pump and fuel filter (carb was replaced a year prior to this problem), it STILL continued. I ran a new gas line to fuel pump and from a gas can....it ran great. Found a split gas line from fuel tank to fuel pump. Replaced the line. Problem resolved.

How did you find the split in the gas line? Was there a drip?

I'm just now having my Onan 5500 die after 10 or 20 minutes . . . . mostly after driving. During 2 previous "tests" it ran for a full hour (1 AC unit 75F temps then later both AC units in 95F temp). Then I went and refueled and it died after an hour with driving - right after I parked it in the driveway. I rarely go more than 4 weeks without a trip and frequently every 2-3 weeks. BTW, it's not the gas cap . . . .

If you look at RDG's pump from Amazon (direct Onan part) there's the same symptoms from other users. Thanks for posting RDG!

I'm thinking fuel pump.

Best,
- bob

[booty51]

So old age and 80,000 miles causes the the crud and tar to ooze out of the fuel pump?

[udidwht]

Quick tip:

Prior to filling up and storing RV purchase big bottle of Stabil fuel stabilizer put in tank then fill. Kick on generator and run for 15 mins or so. Then shutdown.

This will prevent the fuel from not only spoiling but from getting slugged up in the carb. It will last up to 2 years storage. I do this prior to storage and have never had any issues.

[427435]

booty51 wrote:
sounds like the ethanol in the fuel is deteriorating the fuel lines or the fuel pump.

If so, it took 15 years and 80,000 miles of running. I'm more inclined to say it was old age and possibly heat from the engine.

[GrampaR123]

427435, thanks for posting your fix. So many times people get their problem solved but don't take the time to post the result. Then we are all left wondering.

[RDG]

For future reference. These are for my Onan 5500 generator.

Fuel Pump

Fuel Filter

[booty51]

sounds like the ethanol in the fuel is deteriorating the fuel lines or the fuel pump.

[427435]

I just finished replacing the fuel pump (and fuel filter). It started and ran fine for 40 minutes with both air conditions as load. When I got the old pump off, there was a bunch of tar-like crud oozing out from the bottom of the crimped end. Something was going wrong inside the pump. Hopefully it's fixed for a while.

[Rick_Jay]

soxbrat,

What brand is your generator? Is it an Onan 5500 or 7000 by any chance? I know that many of these are very sensitive to oil level, and in my case, oil weight. Mine used to shut down frequently while traveling on the road in hot (over 90 degree) temps. I was using the multi-viscosity oil Onan recommended for the temperature range (5W30...I think, but would have to check.). I discovered that the oil level would drop a bit while traveling, so then I got into the habit of checking/topping off the oil level on the generator before and after every trip. That helped, but it would still, on occasion, die...especially after going over a pretty severe bump or road heave.

I switched to straight 30 weight oil (also recommended by Onan) and haven't had the problem since. I know the multi-vis oil was supposed to be as thick as 30W in the heat, but I don't think it was, and thus sloshed around a lot more. That's the only thing I can think of.

I don't know if your issue is related to the oil, but I do know that the oil level shut-off switch on these Onans can be very touchy.

Good Luck,

~Rick

[soxbrat]

Rick Jay, I put those amp readings in for a reference.I don't know if they're relevant or not. Electronic problems are my Achilles heel. I fairly well understand mechanics, not so much electronics. I removed this 2nd pump a couple of years ago because I couldn't get the gen to even start. Why it will run with it now, i have no idea,lol. My thought was that the pump was drawing excessive amperage and tripping a self-resetting breaker. It would run for 15 minutes, die, wait 5 minutes, start, run 5 minutes, die, etc. My next option is to go to a repair shop and I hate to pay some one to fix a problem if I can fix it myself. Keeping my fingers crossed for now.

[Rick_Jay]

soxbrat wrote:
Here's what solved my problem, yesterday. Started the genset. it ran for 3 minutes before surging and dying. It wouldn't restart. Amp draw was a consistent .78 amps right up to engine shutdown. I happened to have another, used, pump that I installed. This pump showed .80 amp draw. Generator started, powered up and ran for an hour with A/C running. I'm calling this problem solved. A new pump from Cummins was about $120 so it's not an inexpensive fix, but it was simple to get to and only about a 5 minute swap so you shouldn't have to pay to have it replaced.

I hope you found the problem, but I don't know if I'd make the same conclusion about the fuel pump being the issue with the currents you measured. The difference between 0.78 Amps and 0.80 Amps is only about 2.5%. That's within the range of accuracy on DC current scales of many DMMs and Multimeters, so depending upon the meter you're using, it might not be an accurate indicator. Plus, knowing NOTHING about the electrical specs for the fuel pump, that variation may well be within the operating specs as oftentimes the ranges seem to be around + 5 % or even + 10 %.

Now, the fact that putting a different fuel pump in kept the generator running...then that is obviously a good sign. 🙂 Just not so sure you can make that determination from the current measurements.

I hope your diagnosis is correct. Please keep us posted on longterm operation.

~Rick