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Old 10-06-2021, 02:34 PM   #1
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Onan 5500 shutting off with A/C Running

Hello!

I have a 2008 Fleetwood with a Onan 5500 gas generator. It started acting up last year, and was throwing a code, which I don't recall now, which was saying there was an issue with the coils. The generator would fire up and run great, but after I put the coach AC on it would eventually just shut down. I will also mention I did a new OEM Onan fuel pump and filter last year as well. To me it seemed to be getting real hot, and of course we need the coach AC when its hot outside. We live in Temecula Ca, so it at times can be easily over 100 degrees outside. Just two weeks ago the shop that does all of my maintenance on my vehicles and RV ( They have an RV lift, and specialize in RV repair, and have a certified Onan mechanic on site) dropped the generator, cleaned everything up, which they said it was surprisingly clean, replaced both coils, adjusted the valves, replaced the fan belt and tensioner and replaced a few seals/gaskets. I was hoping this would fix the problem but during our trip this last weekend I ran the generator and coach AC to our destination, about a 30-40 minute drive, all was good. Within about 30-40 minutes after I parked, the generator just shut off, while the AC was on. I turned the AC off, but also noticed if I go to restart the generator right after it shuts down, it wont start, it doesn't even prime, like the fuel pump isn't doing anything, not sure if this is normal. When I wait about 30 minutes to an hour it starts up again and runs great until I turn on the coach AC, then it will eventfully just stop running. There is no code being stored. Any ideas or thoughts on what could be going on? Could it be a vapor lock? By only when the coach AC is turned on when the generator is under a heavy load?
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Old 10-06-2021, 07:17 PM   #2
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Best Idea is to get those codes and start there. Find out what the code or codes are and go through the diagnostics for the codes. It sounds to me like you are having a heat related shutdown, like either a protective system is working as designed, or a component is failing when hot like the oil level sensor if it has the low oil shutdown. I would make sure the cooling blower is not obstructed when the unit is mounted in the coach, and that it cannot draw anything over the opening.
Have you tried running it with the AC on and the door to the generator bay open to see if it shuts down or extends the time it takes before it stalls? And of course you are running the correct oil, I believe that year may call for 10/30 for most weather, and if you using straight thirty it could contribute to the problem.





Off topic, man Temecula has blown up since I lived in Poway in the 90's.
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Old 10-08-2021, 07:07 PM   #3
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Just to tell you a story... on mine 5500 nearly same problem.. many parts later.. found old rubber hose had tiny cracks.. but kicker is many lonely days later found critters ate tiny hole where hard fuel line transition to rubber on top of tank.. also clamp rusted off.. so.. gen f/p would work great full tank, but suck air at anything less..
SO try to bypass fuel tank altogether.. hook up fuel line from 5gal can to fuel pump.. bleed out air.. and retest..
When things go haywire and don't make sense keep critters in the back of your mind all the time.. critters find old rv tasty wires and rubber hoses and lines on rv.. critters make nest, webs, shorts and just find ways to ruin thing..
I had to use cell phone with camera and flash and record up under tank and frame and special bore scope camera to find out
Good luck and let us know what you did and maybe better members then me will help you
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Old 10-11-2021, 10:13 AM   #4
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Thanks donr103 and RealNiceTent for the ideas for troubleshooting. During the times it shuts down there is no code, so I have nothing to go by regarding troubleshooting with regards to any type of factory code. Regarding the rubber fuel lines, a buddy told me he had issues with all of the ends of the fuel lines being old and cracked, causing them to suck air, so he trimmed all of the ends and his issue went away. I also talked to my mechanic who said because of the heat where we live, he has had to on numerous occasions relocate the fuel pump away from the engine, as they were getting to hot. This made me think, my Generator only shuts down when its extremely hot outside, and with the AC on. My exhaust pipe from the Generator literally runs right below the fuel pump, I'd say maybe 5'-6" below it. Could the exhaust be overheating the fuel pump, especially with the AC on since the generator is now running at a slightly lower RPM with the load of the AC, so not as much air flow? Unfortunately our weather just changed, so we are not expecting tog et any more heat until next summer. I'll probably check all the fuel lines and my buddy and donr103 suggested, and also relocate the fuel pump and get it out of the heat. I just did a full service on the generator last season, oil, plugs, air filter, etc. And I do believe I used Onan factory oil I got from our local RV shop when I picked up al the tune up parts. Cooling blower is not obstructed, we just removed the generator and cleaned everything, and installed a new fan and tensioner. I did run it while camping during the same trip I mentioned in my post above with the coach door open, it didn't seem to make much difference. I'm really leaning towards the fuel pump and fuel getting to hot and vapor lock or something?
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Old 10-11-2021, 10:51 AM   #5
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The fuel pumps are fairly cheap and are not hard to install. We replaced our fuel pump after our generator would crank and run for about 10 minutes and then shut off. We could crank the generator once it cooled off but once hot it would cutoff again. A video on YouTube showed how the pump once it got hot had a dramatically reduced fuel flow. We replaced ours and nearly 1 year later no issues.
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Old 10-11-2021, 10:52 AM   #6
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Quote:
Originally Posted by brunson67 View Post
I also talked to my mechanic who said because of the heat where we live, he has had to on numerous occasions relocate the fuel pump away from the engine, as they were getting to hot. This made me think, my Generator only shuts down when its extremely hot outside, and with the AC on. My exhaust pipe from the Generator literally runs right below the fuel pump, I'd say maybe 5'-6" below it. Could the exhaust be overheating the fuel pump, especially with the AC on since the generator is now running at a slightly lower RPM with the load of the AC, so not as much air flow?

Sounds like the fuel pump might be shutting down on an internal overload/over-temperature protection device. That exhaust pipe can radiate a lot of heat, and more still when it's running hard. Can you strap a temporary piece of heat shield between the pipe and the pump, for testing purposes? Almost anything will work, as long as it can't catch fire of course. Something shiny is best, like some metal flashing or a cut in half metal can.
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Old 10-11-2021, 10:55 AM   #7
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Sounds like the fuel pump might be shutting down on an internal overload/over-temperature protection device. That exhaust pipe can radiate a lot of heat, and more still when it's running hard. Can you strap a temporary piece of heat shield between the pipe and the pump, for testing purposes? Almost anything will work, as long as it can't catch fire of course. Something shiny is best, like some metal flashing or a cut in half metal can.
Yes, I was thinking the same thing, some type of heart shield might do the trick. Maybe even clamp something onto the actual exhaust tubing.
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Old 10-11-2021, 10:56 AM   #8
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The fuel pumps are fairly cheap and are not hard to install. We replaced our fuel pump after our generator would crank and run for about 10 minutes and then shut off. We could crank the generator once it cooled off but once hot it would cutoff again. A video on YouTube showed how the pump once it got hot had a dramatically reduced fuel flow. We replaced ours and nearly 1 year later no issues.
Very similar situation. Think I'll do a new fuel pump, and either relocate it, or do a heat shield.
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Old 10-11-2021, 10:59 AM   #9
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Aircraft Spruce sells all sorts of heat shields for exhaust systems and other parts. This product description even mentions RVs, but there are a number of different products.

https://www.aircraftspruce.com/catal...All%20Products

The OP could also insulate the pipe with exhaust insulation, similar to how some turbos are insulated, but I suspect that if heat is the problem, a simple shield would be enough.
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Old 10-11-2021, 01:03 PM   #10
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Aircraft Spruce sells all sorts of heat shields for exhaust systems and other parts. This product description even mentions RVs, but there are a number of different products.

https://www.aircraftspruce.com/catal...All%20Products

The OP could also insulate the pipe with exhaust insulation, similar to how some turbos are insulated, but I suspect that if heat is the problem, a simple shield would be enough.
Yes, great idea using exhaust wrap, that could definitely help. I'll check out the website you listed as well.
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