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Old 01-14-2014, 11:31 AM   #1
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Generator surging/searching

Stopped to dry camp overnight and ran the generator for about an hour using several appliances. All of a sudden the generator began hunting up and down. Didn't seem to matter whether I had a small load or heavy load the generator would continue to search up and down in small RPM increments at each load level. Never experienced this before. Any suggestion as to where to start looking for an answer.

Jerry and Judy
Fremont, California
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Old 01-14-2014, 01:00 PM   #2
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Don't think you will get too much response until you tell us what make/model generator you have and what it's installed in.

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Old 01-14-2014, 01:09 PM   #3
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Diesel or gasoline? Generator capacity? Load in watts?

We need more information.
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Old 01-14-2014, 01:18 PM   #4
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I would suspect a governor issue whether it's mechanical or electrical
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Old 01-14-2014, 02:15 PM   #5
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To the previous responders I should point out that this is the Alpine Coach Forum and Jerry says he has an 05-06 36 ft model. All Alpines use the Onan QD 7500.

If you have fuel well over the 1/4 full mark I suspect you may be having a problem with the inverter/controller unit. The only fix for this is to replace it with a new one and it is not cheap. You may need to find an Onan dealer that can check it for you. I had 2 fail on me and the last time I bought a new generator rather than fix the old one again.
P.S. I assume you are not getting any blink codes?
John and Mary Knight
2015 Newmar Ventana 4311 - wheelchair accessible
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Old 01-17-2014, 11:50 AM   #6
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I'd start with new fuel and air filter if they have not been replaced in a while. I would also check for a fuel hose cracked letting air into the fuel system before spend a lot of cash. Let us know the fix? Thanks
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Old 01-17-2014, 12:10 PM   #7
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Assuming for the moment this is a gasoline or propane generator (My knowledge of Diesels in the area is ... Non existent) as I recall if the engine is running LEAN it misfires.. if it's running RICH, in many cases it does just as you described, Speeds up and slows down speeds up and slows down.. NOTE that I may have lean and rich backwards but I think I got it right. been over 30 years since I worked as a small engine mechanic in a chain saw shop and my chain saw is..... Electric.

Rich could be caused by an improper altitude setting on the carb (ONAN has those) dirty air filter, or automatic choke as well as the metering screw.. You really need the manual (Service type) to make adjustmetns other than Altitude.. Set it for sea level and see if it helps. If it makes it worse, Set it for Denver (Mile high)..

Also, replacing filters as suggested by others.. Likely this should be the 2nd step in any "Runs rough" problem,, Step one is a good visual inspection.
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Old 01-18-2014, 12:02 AM   #8
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This is the Alpine Coach forum, as Algoma pointed out all Alpines have the 7.5 Kw Quiet Diesel Gen set.
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Old 01-18-2014, 06:18 PM   #9
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The Onan Quiet Diesel 7.5kw generator in our coach sounds like like it's hunting at times. I put a meter on an outlet and monitored voltage and AC cycles. It's rock steady at 60 Hz and 119.8 to 120.2 volts. The change in sound is the generator reacting to the load, the output is fairly constant - as good as residential in my opinion. Much better than than any gas generator I've tested.
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Old 01-18-2014, 07:07 PM   #10
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Jerry reported that his generator was changing speed regardless of the load he was putting on it. The Onan is a variable speed generator that will speed up as the load increases but what he described is not normal. Usually if there is a problem the light on the switch will flash an error code but this did not seem to happen in his case.
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Old 01-19-2014, 06:51 AM   #11
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Generally speaking, the "load" applied on the coach needs to be measured in "AMPS" not voltage. The generator will/should maintain a relatively constant voltage (as measured by Koop) regardless of the load (AMPS). Either something in the coach is varying its load or the generator has a problem and not able to properly determine the load.

As an example, the inverter/charger is one device that tries to keep the batteries charged and therefore draws "AMPS" from the incoming A/C (shore power or generator). If the inverter/charger is exhibiting a problem it could be the source of the varying load. The monitor panel for the inverter/charger would hopefully indicate that variance. Hopefully your batteries are fully charged otherwise the charger might be reacting to the generator problem.

You would need to measure the "AMPS" on the load circuit for the generator. You probably need to take it to an Onan certified dealer for proper diagnostic &/or repair.
Bob Bowers (Surprise, AZ)
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Old 01-19-2014, 06:55 PM   #12
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As stated this is the alpine forum, alpines are equipped with either 7.5 of 8KW gensets depending on what year it is, mine is an 8KW and it's a 2007. All are onan.

First change the fuel filter and air filter, do an oil change if one has not been performed within the last 150 hours of operation. Make sure your fuel tank is half full because many times WRV hooked the fuel pickup to the wrong pipe connector in the tank. FWIW-if Hydro/aqua hot equipped that fuel pickup is 3/8 tank full, the genset is 1/4 tank full. WRV as stated reversed those lots of times. To make sure it is not fuel related, fill up the tank to full, and then try it again, after air and fuel filter change. If that fixes it, then do the fuel filters on the big engine, and put in a couple of quarts of the green cap/bottle of Power Service Fuel Cleaner, run the coach for 50 miles and return, check operation again. That should fix it unless it's a deeper problem. Start cheap and work your way up to expensive.

It's nice of owners of other coaches to offer assistance, but it's been my experience, you have no working knowledge of Alpines, as they are their own breed of MH, and my second observation I cannot publish here.
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Old 01-19-2014, 07:20 PM   #13
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How long has it been since you ran the generator before this time. The best way to monitor output of a generator is by the frequency. As the engine slows down and speeds up the frequency will follow it. If you have a meter that will read frequency they checking it. The volts and amps will also be effected, however frequency is the best indicator of engine speed change. As has alresdy been mentioned change oil, oil and fuel filters, and check fuel line first.

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Old 01-19-2014, 07:33 PM   #14
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chboone, I can only assume you have never owned an Onan QD generator.

John and Mary Knight
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