Onan 5500 Generator Dies

jeffwelsh · 03-09-2015, 04:23 PM

I have a strange problem with my generator. The Onan 5500 will run for a random amount of time usually over an hour. Somewhere around the hour to hour 30 mark it will start to spudder and die with code 36. That code translates to the engine stopped for some unknown reason. It sounds fuel starved. It will restart after priming and cranking for a while and run for a random period of time again (usually much less time, like less than 30 minutes before the cycle repeats.)

I check the fuel filter and it was ok and blew back through the line and could hear gas gurgling in the gas tank. I have read other forums and thought it could be the fuel pump. I saw where onan has a new part number for my fuel pump and ordered one of those. I just got to test it again yesterday with the new fuel pump and had the same thing happen. Oil level is fine the genny only has 10 hours on it. I hate to leave the 3605 at the dealer for who knows how long. Any other suggestions for trouble shooting.
-Jeff

wildwest450 · 03-09-2015, 05:37 PM

While I can't be of any help, it's nice to know in the age of advanced electronics, there's a code to tell you your engine stopped running.

sundancer 87 · 03-09-2015, 06:10 PM

I'm wondering if the vent hose for the generator gas tank is crimped? If it is the generator, while running, is pulling a vacuum on the tank and basically running out of gas.

You could run the generator until it stops, run back to the gas tank and remove the gas cap. If you hear the whoosh you know the tank had a vaccum on it. Or you could run the generator with the cap off the gas tank and see what happens.

jeffwelsh · 03-09-2015, 07:41 PM

Thanks, I will try that. It still could be the fuel pump. I did get a different code this time. I ran it with the cover off and I remember the guy doing the PDI said not to do that since the generator could over heat. I'm working from home today and fired it up earlier. We are at 1:40 minutes and so far so good!

arlan in arizona · 03-09-2015, 08:07 PM

Good luck with the fuel pump. Mine was acting similar to what you are describing. A new fuel pump fixed mine.

jonthefireman · 03-10-2015, 12:55 PM

Has happened to me a couple of times, but always fires right back up. I wrote it off to just being mechanical and sometimes things don't go perfectly, but admittedly I haven't boondocked that much so I don't have much to go on. I did do the first service myself, changed the oil/filter and such and ensured everything was tip top.

jeffwelsh · 03-10-2015, 02:19 PM

Update:
I put the cover on the genny and ran it yesterday. It ran for over 3 hours without any problems. Thats the longest its ever run without quitting. I think the fuel pump may have been the issue. For future reference my old fuel pump was part number A029F887. I found where A047N929 replaced that part. They looked identical on the outside.

I saw on another forum where ONAN did have problems with Chinese made pumps where they would get hot and a seal would expand and lose vacuum. That could be why the part number changed or their could have been an engineering change.

If I have problems in the future the next step is to check for a vacuum in the tank as sundancer suggested and if that looks good its back to Holman and let them fight it.

Thom · 03-10-2015, 05:09 PM

Quote:

Originally Posted by jeffwelsh

Update:

I saw on another forum where ONAN did have problems with Chinese made pumps where they would get hot and a seal would expand and lose vacuum.

Oh No, say it isn't so! I have to fight with the Chinese made carb on my weed eater every time I pull the starter rope....

WifiDan · 04-16-2015, 02:33 PM

We have a brand new unit and the generator is doing the exact same thing. Unfortunately I have the fuel pump with the newer part number you mentioned.

jeffwelsh · 04-21-2015, 05:33 PM

I work only about 10 minutes from the Onan Service center in Cincinnati and talked to them about the problem. They said not to be surprised if the new pump is bad too. They said they have had a ton of problems with those pumps.

Code 36 is a catch all an pretty much indicates a fuel issue somewhere. I have not had a chance to get back into mine. The next trouble shooting step is to take the pressure side loose when it is acting up and check fuel. I will post more when I think I get this totally resolved.

WifiDan · 04-21-2015, 06:33 PM

Please do! I am going to try a new pump before our trip this weekend and update if it fixes it!

sundancer 87 · 04-21-2015, 10:21 PM

FWIW, I had a Honda 6010 motorhome generator to power the A/C when I lived in a solar home. The fuel pump died so I, like many others, checked the OEM prices. Very pricy for that pump, same as the cooling fan that went away on me.

I went to Auto Zone and had them pull me an electric fuel pump off the shelf. Took it home and installed it on the Honda and it only lasted 8 years before it was time for another none.

If one can find the specs on the Onan pump a cheaper pump may work. It's pretty much a pressure/volume thing so I doubt Onan has a proprietary pump but they do want you to use theirs but there's always another way to skin a cat.

jimflyjim · 06-07-2015, 09:13 PM

hey sundancer that onan doesn't even need a pump ,as long as your fuel supply is higher than your carb it will run on gravity feed ,or just about any generic elec pump available for small engines .one time I used a kawa.ninja 600cc elec pump to run a onan4000

sundancer 87 · 06-07-2015, 09:38 PM

I'd say my fuel tank is just about the same level as the fuel pump on the generator, not including sags in the fuel line.

jeffwelsh · 08-11-2015, 06:56 PM

Update: Since my unit had to go back to Holman's for the dump cable replacement, I decided to give them a couple other things to look at, including the generator problem. They had it 6 weeks and found the fuel line was kinked and replaced it all. It was probably getting sucked closed. We will see if this is the fix or not. Right now I'm not too optimistic, since its about an hour drive home and I started the genny to run while I was driving home. Upon arrival it was not running. I started it later and it ran for over an hour before I had to shut it down before I left. We will see, but I'm probably going to add a booster pump at the rear. My thought is going up some long hills, the pump is simply not strong enough to suck the fuel that far up hill. I will keep this updated until I think its really fixed.
-Jeff

Pirate · 08-19-2015, 03:22 AM

I did a post on this issue in early July. The solution was adding a second electric fuel pump back by the Generator fuel tank.

Problem solved!

I believe its due to the fact that the Onan fuel pump is right at the generator and is pulling fuel from a tank at the other end of the rig.

Add to that the heat, both the ambient air around the generator, and head that been rising off the hot highway.

And you have the perfect situation for vapor locking and/or the pump sucking the fuel line closed.

When I cut into the fuel line to put the second pump in...it looks like good fuel hose with the fiber thread woven into it. Nope, cut it and the outer hose has fiber woven in, but its pretty thin. The inner hose is softer than vacuum hose...so it can be sucked flat pretty easily when hot.

Adding the second fuel pump solved the problem completely. Our Voltage has a 5500 Onan. After adding the new pump. Fired up the generator, gave it a couple of minutes to steady out. Then on with on AC unit. Then on with the second AC unit. Then on with the refrigerator. Then on with the electric hot water heater. Then on with the TV. Then on with the microwave. Then on with the fireplace.
And the generator just purred along. Left everything but the microwave and fireplace running for three hours and nary a blip!!

Dry camped for four days a month later and never missed a lick.

Pirate

WifiDan · 08-19-2015, 05:32 AM

That's great! Where did you get the fuel pump and what model? Also where did you wire it into?

Pirate · 08-19-2015, 07:04 AM

This is where it got a bit difficult....

I did the addition in Fillmore, Utah...the only auto parts store was a Carquest so I went in asked about an electric fuel pump. They had two, a little bitty thing, and one that was nearly 3" in diameter. Having a little experience with electric fuel pumps in the past...I bought the big one. It was about $90. I bought two 5/16" tube x 1/4 male NPT nipples and four 1/4 x 20 bolts and Nylock nuts.

Held the pump in place on the outside of the frame, marked the first hole and drilled it. Installed the nut, tightened pretty well. That held the pump in place and I drilled three more holes using the holes in the mounting bracket as a template.

Threaded the nipples into the inlet and outlet and, with the pump bolted to the frame, tightened them in with a Gear Wrench. If you don't have yellow, use with gasoline, Teflon tape, don't use anything on the threads. They'll seal.

Cut the fuel hose, drained it, slipped hose clamps on either end, shoved the hose on the brass nipples, tightened the clamp. Done.

Now, all you need is a hot wire, the mounting bracket to frame is your ground.

Turns out Dutchmen runs a 2" ABS tube from just behind the Generator all the way back to the fuel tank.

I didn't have mine as I was away from home, but look behind the generator and you'll find the ABS tube. Run a wiring fish tape through the tube back to the end at the fuel tank. Use 14ga red stranded wire, and pull it from the tank end up to the generator end.

Mine Voltage has the "black plastic cardboard" belly cover. So I took the cover off the Generator and the front panel...and voila! There was the fuel pump. Pull the red wire to the location of the pump and splice it into the hot wire to the Generator fuel pump. This way the two fuel pumps run anytime the Generator is running. Use a crimp butt connector to connect the red wire and the wire on the new fuel pump.

Prime the Generator and have someone listen back at the new pump to make sure it runs.

Fire it up...put away tools...and listen to the Generator purr!!

Pirate

arlan in arizona · 08-19-2015, 08:20 PM

Good post. I have only had my generator quit twice. Both time were driving through 100+ degree temperatures and spots in the road that were extremely bumpy. I like the thought of a second or backup fuel pump. I have that on my "to do list" when it cools off out here.

Pirate · 08-19-2015, 08:58 PM

I got that tip from a good friend that has had several Toyhaulers. In his first experience with the Generator quitting it was the dealer that told him of the fix and eventually paid for the second fuel pump.

I sense the issue surrounds the fact that the pump at the generator is a centrifugal pump, not a good 'ol positive displacement pump like autos used to have. Thus its really not capable of "pulling" fuel a long way.

Just thoughts,

Pirate

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