Onan Generator

[Barbara Nester]

I have an onan 5500 generator.  We have had the problem of it not stArting. It just cranks.  4 mechanics have all said it was the carburetor.  The first one took it apart and cleaned it 3 times. Didn?t work second one changed that carburetor didn?t help.  Then said it was fuel pump.  Changed fuel pump to no avail. Still won?t run. Third one put another carburetor still didn?t help  fourth one once again changed the carburetor it fired up ran a minute shut off and same thing will crank but won?t fire. Oh yes mechanic 3 also put in new spark plugs.  Now mechanic five has come and said it was out of time so he removed it called and said you guessed it.  It is the carburetor.  How is it possible that there are 4 bad carburetors in a row.  Are there fuel shut offs that are a safety feature on this generator?

 

[NY_Dutch]

The generator needs fuel, air, and spark timed correctly, to run. Did anyone check for spark? Once it starts, Onan generators need to see a minimum voltage to keep running, but that can be tested by just holding the start switch on to see if it keeps running. If it does, it's an electric side problem, not an engine side problem.

 

[Isaac-1]

You need to take it to an Onan certified technician

 

[Kevin Means]

Welcome to the RVForum Barbara. This may seem like a basic question, but how much fuel was in the RV's gas tank when you tried to start the generator. The fuel pick up for the generator is at about the 1/4 to 1/3 level on the gas tank. The generator won't start or run if the gas tank doesn't have enough fuel.

You didn't say how long it's been since the generator ran properly, but it's not uncommon for a gas generator to not start, or not stay running, if it hasn't been used in awhile. If that's the case, the carburetor is usually the culprit, because its insides get gummed up when the fuel gets stagnant. That's probably why the people who serviced it swapped it out. Having said that, it is highly unlikely that four new carbs were defective.

Like Dutch said, the generator needs spark, fuel and air (at the right mixture) to run properly. It's easy enough for a "qualified" technician to check for all three, but sometimes those people are hard to find. The generator has some safety features to protect itself (output frequency, voltage, oil pressure, over-temp etc.) but I believe the generator has to be running for those features to work. In other words, it has to be running - at least for a moment - to detect trouble.

Are you getting any flashing lights on the start switch when you try to start the generator? If so, the number of flashes corresponds to a fault code, which can help diagnose the problem.

Kev

 

[namumac1]

Don't know about your's but mine has a fuel shut off valve at the tank. Also, how old is the fuel and was it treated with stabilizer? Try to use stabilized E0 fuel. You'll have a lot less problems. Do you shut off the fuel supply and run it out of gas before you store it for awhile?

 

[NY_Dutch]

Don't know about your's but mine has a fuel shut off valve at the tank. Also, how old is the fuel and was it treated with stabilizer? Try to use stabilized E0 fuel. You'll have a lot less problems. Do you shut off the fuel supply and run it out of gas before you store it for awhile?

Her Onan 5500 is an onboard generator that gets its fuel from the RV fuel tank, not a portable with its own fuel tank.

 

[Arch Hoagland]

On most RV's if you get down to a quarter tank of gas the fuel is shut off. 

How much gas is in your gas tank?

 

[NY_Dutch]

On most RV's if you get down to a quarter tank of gas the fuel is shut off. 

How much gas is in your gas tank?

If I'm reading the OP right, the 5th tech pulled the generator to take to his shop so the RV gas tank level shouldn't matter in that case.

 

[Arch Hoagland]

If I'm reading the OP right, the 5th tech pulled the generator to take to his shop so the RV gas tank level shouldn't matter in that case.

Yeah I saw that...just covering all the bases.

 

[jubileee]

  About 30 years ago a buddy had a Onan in motorhome that would not start. Had air, fuel, spark, and good compression. Brought it over to my truck shop.  Fired the parts canon at it. Nothing. Turned out the key on the crankshaft for the flywheel had worked out and threw the ignition timing off.
  Generator only had couple hundred hours on it.
  Found key in bottom of generator case. Easy fix.

 

[Isaac-1]

Sheared key is a known issue on these also, I would not call it rare, maybe uncommon, but you are by far not the first person I have heard of having that problem.

 

[Rene T]

I don?t know about your generator but some have a safety feature that the generator won?t run if it?s low on oil. Anyone check the oil level?

 

[Barbara Nester]

Tank was full flash codes were checked.

 

[Gary RV_Wizard]

We here are doing exactly what that string of psuedo-mechanics did - toss out common problems as "maybe it's this" solutions but avoiding any actual diagnosis. When a gas engine won't run and none of the quick & easy actions get it going, you have to go back to the basics - air, fuel & spark. Each of those can be verified and a professional tech will know how and do it, while shade-tree mechanics just keep guessing and throwing parts at it.
You didn't mention anything about those mechanic's credentials, but small engine repair is a specialist field.  Automotive or heavy equipment mechanics often fail at small engines.


At this point and with 5 failed attempts to fix it, I'd go to the pros at an actual Onan shop where they know these gensets inside out and have the tools and techniques to properly diagnose what actually is or isn't happening.

 

[NY_Dutch]

This link may help in finding a certified Cummins/Onan service center:

https://www.cummins.com/engines/motorhome-and-rv/find-motorhome-and-rv-service-location

 

[namumac1]

Her Onan 5500 is an onboard generator that gets its fuel from the RV fuel tank, not a portable with its own fuel tank.

OP didn't say where the generaton was mounted, could be a 5th wheel or a tag along.

 

[NY_Dutch]

OP didn't say where the generaton was mounted, could be a 5th wheel or a tag along.

"Now mechanic five has come and said it was out of time so he removed it..." That tells me that he would have used an external fuel supply for testing.

 

[JayArr]

Hi Barbara

There are a lot of really cheap Chinese knockoff carburetors on the market, if your mechanics have been buying the $75 knockoffs instead of the $300 Onan then it's very possible that you have had four bad carbs in a row.

 

[DonTom]

Hi Barbara

There are a lot of really cheap Chinese knockoff carburetors on the market, if your mechanics have been buying the $75 knockoffs instead of the $300 Onan then it's very possible that you have had four bad carbs in a row.

Try less than $40.00.


Notice the reviews are all over the place, just like with  most product reviews. Around 50% say it works perfectly, and 20% says they are pure junk.  I just put a cheap one on my generator, but I have other issues (bad starter) that I have to fix. I will report back how the $40.00 carb works for me when I have mine running again in a week or so (waiting on the starter and other small parts).


I think it's unlikely that the cheap carb would make the generator not run at all. Notice even  the worse reviews above got their generator to work, in most cases, just would not run correctly.  And most who review a product is when they have a problem. Less will say it works just fine, even when it does.  I am guilty of that myself.  I will always review something that gives me a problem, but rarely when it works as advertised.


-Don-  Auburn, CA

 

[skydivemark]

How about the possibility of fuel pump sucking air in thru a dry rotted fuel line. If it ran good at a shop - not installed in the RV - that's where I'd start looking.