My ONAN 5500 finally fixed

[allcool]

As some might know, have been having problems with my Onan for years, ever since I got it.

Started with checking fault codes, they translated to needing new carb, to get it running at all. Tried to clean old carb to no avail. It did get better, but still not right.
Some of Those fault codes couldn't be any more vague or harder to interpret for the layman not familiar with Onan's.

Installed a new carb. Adjusted/set up the HZ, checked it under full load, it was perfect.
New carb seemed to do the trick, for a day or so.

Then I noticed the gen would run for maybe 1-5 hours perfectly, then quit. It would restart immediately, then usually shut right back down in minutes. If I waited a hour or so it would run again for a while.

Don't get me wrong, when it was running it ran flawlessly. It just stopped running randomly, sometimes after running under full load, 2 a/c on for hours. Sometimes it would run for a full weekend trip, starting and stopping correctly whenever needed, no problem.

Did a full gen service, oil, filters, etc, many times. Gen had 24 hours on it when I got it. It now has 427 hours.

Seemed like whenever the fuel got less than 1/2 tank, the problem would arise.
Tried the gas cap off vent the tank thing, no change.
So tried a new fuel pump. No change.
Tried a can of gas connected directly to the fuel pump with 3' of tubing, bypassing the fuel tank and its fuel supply line. No change.

So as you can see, this was an intermittent problem. But a problem none the less. The gen would stop at the worst times possible. Like on a hot night early fall at the dunes. With both ac running and just cooked a nice big dinner. 8 of us just sat down to eat, wouldn't ya know it, yup the gen quit, no more ac.

This type of intermittent problem went on for 2+ years...
I Couldn't figure it out.

Then started noticing when the gen would shut down. It seemed to happen shortly after I turned off the load that was on it. Or when the load would cycle or change. Like when an ac would cycle off, on the thermostat. Or the microwave would shut off. And the battery charger/converter had already fully charged the batteries.

So this got me thinking, and went back to basics. Checked the fault code again. hadn't done that since I replaced the carb. Should have. It came up different from the the carb failure problem in the beginning. It was now fault code... 'unable to maintain frequency'.

So whipped out my handy meter, set it to HZ and found 62.7hz. Well, it is suppose to be 60-63hz per the manual. But it was running under load with 1 ac, tv, and converter using ac power. I shut down all loads and then hz started rising, went to 67 or so... then it shut down... Started it back up and immediately started the ac so it stayed running, it ran again at 62.5 under load.

Hmmm, we're getting somewhere now. After some reading in the manual and online, found out the control turns off the genny at 67-68 hz as to not damage anything from to high HZ.

So now it was time to readjust my HZ like I did when I changed the carb. Was sure I had set it right to start with a couple years ago..? I doubled triple checked checked it back then...??? Hmmm maybe something wore out or changed...

Started to turn the nut that adjusts the governor spring/arm to lower rpm thus lowering the HZ. With my meter right next to me, and gen running under low load, with the converter and microwave on it was at 63.7, to high, so I kept on turning the nut and the hz lowered a little, about maybe 1.5 hz, but it wouldn't go any lower even though i kept on turning the nut... Then I saw it, the wire from the choke was under the arm holding it from going lower. As soon as I moved that wire out of the way, the hz went down to 57. I adjusted it back up to 62. Then proceeded to do the correct hz adjustment procedure with load and without. Ended up with 59.5hz with both ac, and microwave on. With no load on it, it was at 62.5... perfect.

It hasn't missed a beat or turned of since. And the 'fix' was on my Halloween dune trip. Have been out 3 times since then and for 7 days over the New years. It doesn't shut down intermittently any longer.

Guess my attention to detail when the carb was replaced originally was less than enough. At full load that wire wasn't close to holding the arm up. What I didn't realize, was that arm moves quite a bit, and that wire can't be anywhere close to the arm, or it will hold up the arm not letting the rpm drop enough when the gen off loads.

Just thought I'd pass this along in case anyone else has a similar problem. Check your choke wire and get it far far away from that governor arm...

[rcpd34]

I was just referred to your post. I'm having a similar issue; you can read about it here: Odd Onan Issue
After reading it, I realized I had read it at the time you posted it, but forgot about it. I hope to get over the the RV today and see if your solution will work for me. It's a great read.

[mrxlh]

Preference I guess, never saw a Fluke respond fast enough, even on a 900 RPM generator. This is of course setting up 2 or 3 gen sets that have to be able to sync.

[allcool]

mrxlh wrote:
If you or anyone you know that has a analog multimeter, it is an absolute must when adjusting the governor.

Not sure why you think its a must to use an analog meter..? please explain why..?

Being old school I have both(actually many of both). Other than the older, very inexpensive, slow to respond, low quality digital meters, I see no reason a good quality digital meter can't be used.

My Fluke digital meters have a very fast sample response rate and work great for HZ or anything. My much cheaper uei meters, also are plenty fast enough to adjust hz on a gen-set, no problem. Actually that's the meter I used to adjust my Onan 5500 to perfection.
I did double check HZ with my 40 year old Triplett analog meter... Exactly the same as the digital UEI meter reads. 59.5-62.5 hz droop from full load to no load on a HGJAB Onan 5500

JMO

[mrxlh]

Dave, it sounds like it is indeed the governor, almost like it had been adjusted for near surge loading. If you or anyone you know that has a analog multimeter, it is an absolute must when adjusting the governor. It makes really short work of it too, as you can "see in real time" what it is doing when load is applied ad removed.

The easiest way to see if you genet governor is adjusted properly is watch you clock for accuracy, if it gains time or loses time it is running faster or slower than 60Hz, all 120v U.S. clocks are based on true 60Hz.

[allcool]

rkortes wrote:
Amazing job of hanging in there and not giving up. I have a 5500 as well and will keep this post in my favorites for future reference.... Thanks!!

Racerx11 wrote:
Nice job, I bet when you saw it you were pretty damn giddy huh 🙂

mrxlh wrote:
Cool, glad to here you figured it out. In the world of all things digital, this is one area that an analog meter is a must.........adjusting a generator governor to HZ.

nayther wrote:
It's always the "simplest" things isn't it?

Good job.

Thanks guys...

Racerx11, yup was a little giddy and pissed off at myself, when I found the problem.

[allcool]

dedmiston wrote:
I never knew there was an adjustment for the Hz. I adjust the carb for altitude, but I didn't know about the other adjustment. I wonder if this has anything to do with how mine runs rough.

Mine has a roll to it, like it wants to die. It starts fine and runs great under a load, but when it's just charging the batteries it surges and lulls. It never really quits, but it's annoying to listen to.

Could be an out of adjustment governor, or these things can cause your surge/roll/lull/hunting...
"binding governor linkage, fouled spark plugs, improper
valve lash, and dirty fuel filters". Most common imo, would be a gummed up carb...

Not sure of the hours, or state of tune on your gen-set, but if its not been done recently, couldn't hurt to do a 450 hour tune up, with all filters, valve adjustment and plugs. That would effectively rule out those as the possible cause.

If the 'roll' you are talking about is more like the gen-set hunting back and forth for the proper rpm, as opposed to a carb problem, not letting it run smoothly, might try an adjustment...? If its a carb problem, no adjustment will help. Been there done that.

As per the manual, try moving the spring that holds the governor arm a notch or 2(or more) away from the shaft end of the arm. Its a very easy adjustment you can always change it back no harm done(note which notch it was on to before adjustment)... worth a try.

If you can find a meter wouldn't be a bad idea to check hz droop. If the gen-set isn't running smoothly with no hunting then the hz will be changing up and down with the rpm, as will the voltage. But if your gen-set doesn't shut down, then hz are probably close to being in specs or the controller would shut it down.

It should run smooth, no roll, no hunting, no surging back and forth, at all.

page 8-20 onan manual...
"If droop is less than specified, or the genset
hunts, move the spring hook one or two
notches away from the governor shaft and recheck
frequency and droop. Repeat the procedure
as necessary.
5. The governor must not hunt. Check for hunting
under the following loading sequence:
A. No-Load • 3/4-Load • No-Load • 1/2-Load •
No-Load • 1/4-Load • No-Load."

[dedmiston]

I never knew there was an adjustment for the Hz. I adjust the carb for altitude, but I didn't know about the other adjustment. I wonder if this has anything to do with how mine runs rough.

Mine has a roll to it, like it wants to die. It starts fine and runs great under a load, but when it's just charging the batteries it surges and lulls. It never really quits, but it's annoying to listen to.

[nayther]

It's always the "simplest" things isn't it?

Good job.

[mrxlh]

Cool, glad to here you figured it out. In the world of all things digital, this is one area that an analog meter is a must.........adjusting a generator governor to HZ.

[Racerx11]

Nice job, I bet when you saw it you were pretty damn giddy huh 🙂

[rkortes]

Amazing job of hanging in there and not giving up. I have a 5500 as well and will keep this post in my favorites for future reference.... Thanks!!

[allcool]

dieseldan723 wrote:
I love your persistence. It's things like this that I like to read. I am having problems with mine right now and am just starting the process. I hope I find it like you did!

GREAT JOB!

Thanks, just happy I finally figured it out.

Ya, persistence, thats one of my good traits, or some might say anal traits... lol

Now at almost 450 hours on my genset, its time for the major Onan tune up consisting of valve adjustment and plugs. Manual also says to clean or replace cylinder heads at 450 hours...? This 450hr tune up should be a real pita.

Good luck with your Onan problem...

[dieseldan723]

I love your persistence. It's things like this that I like to read. I am having problems with mine right now and am just starting the process. I hope I find it like you did!

GREAT JOB!