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Old 04-10-2021, 02:45 PM   #1
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Onan 5500 stumbles and makes popping noise

Noticed a problem with my Onan 5500 Gold Marquis generator. Started without any problem and appeared to be running OK. Started the bedroom air conditioner and noticed a slight audio "stumble" from the generator. Started the main cabin air conditioner as well. Again, slight audio "stumble", then running OK.

After a few minutes, from the exhaust pipe I hear a "popping" sound that starts to become intermittent and the generator sounds like the engine is about to stall. Shut down the AC units and it appears to be running OK again. Last time I heard that "popping" was from my GM 8.1L Vortec motorhome engine and a replacement of spark plugs and ignition wires fixed the problem. The generator only has 204 hours, but I replaced the spark plugs anyway. See photo of replaced plugs. Note both center insulators are well blackened, but not fowled. Also, plug on left has its entire threaded area black and wet from fuel/oil?

Also, based on info I gathered from a YouTube video about Onan 5500 high oil level causing a stalling problem, similar to what I found, I removed about 1-1/2 pints of engine oil from the sump.

Generator seems to run just fine now with both AC units running at 23 amp load on generator and oil level about 1/4" up from the "Add" oil mark on the dipstick.

However, I think a carb flush with Seafoam and gas mix would be a good PM move, just in case.
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Old 04-10-2021, 09:16 PM   #2
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If carb was gummed up, the spark plugs would be burt white ( too lean) if you have an altitude knob on the carb turn it in 1/4 of a turn clockwise,
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Old 04-10-2021, 09:40 PM   #3
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Also make sure a wasp hasn't made a nest in your exhaust pipe giving you to much back pressure.
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Old 04-11-2021, 07:21 PM   #4
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I pulled the spark arrester plug and couldn't believe the carbon soot that came out with the genny under load. Can't remember how many hours our genset has, but it's pretty low. Anyway, as power demand changes occur, the genset rpms seemed not to fluctuate as much as before.

I think it's one of those 'forgotten' maintenance items.
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Old 04-16-2021, 12:21 AM   #5
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The Seafoam cleaning (may/ may not) help, but generally, if it will run fine for a while/ period, then CARB is fine, and the symptoms more common to LEAN which happens under load for (most), and recommend suspecting (intermittent/ failing) FUEL PUMP IF PROBLEM continues?
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Old 04-18-2021, 07:57 PM   #6
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I would suggest you drain your oil completely and then refill. It takes 2 quarts according to the manual, with a filter change. When full, it looks like it has too much oil, if you take some out, you risk a low oil shutdown if you use it on the road.
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Old 04-18-2021, 10:28 PM   #7
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I would suggest you drain your oil completely and then refill. It takes 2 quarts according to the manual, with a filter change. When full, it looks like it has too much oil, if you take some out, you risk a low oil shutdown if you use it on the road.
A low oil shutdown feature does not stop the engine if level is low, it prevents re-starting the engine when low oil level is detected.
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Old 04-19-2021, 01:09 AM   #8
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A low oil shutdown feature does not stop the engine if level is low, it prevents re-starting the engine when low oil level is detected.
If it works that way, its a complete waste of circuitry to have.

Generators are auxiliary power stations, for long term use when other power sources are not avalable. They are designed to run contionusly, for days at a time.

What good would it serve me having a " re-start low oil lockout ", if while running, my oil level dropped low enough to damage my engine ?

Of course, a low oil shut down feature will shut down a running engine and prevent re-starting it.
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Old 04-20-2021, 10:25 AM   #9
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If it works that way, its a complete waste of circuitry to have.

Generators are auxiliary power stations, for long term use when other power sources are not avalable. They are designed to run contionusly, for days at a time.

What good would it serve me having a " re-start low oil lockout ", if while running, my oil level dropped low enough to damage my engine ?

Of course, a low oil shut down feature will shut down a running engine and prevent re-starting it.
OK, I guess I've never ignored an ICE engine long enough for the oil level to go below the add mark. Thanks for correcting me.
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Old 04-25-2021, 04:27 PM   #10
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Been having the same problem with mine.. Will start popping after 25-30 minutes. Did plugs, fuel filter, fuel pump, spark arrestor adjusted the valves and new carb. However if I feed fuel from gas can instead of coach it will work fine... Maybe a fuel line issue?



Quote:
Originally Posted by geofferyh View Post
Noticed a problem with my Onan 5500 Gold Marquis generator. Started without any problem and appeared to be running OK. Started the bedroom air conditioner and noticed a slight audio "stumble" from the generator. Started the main cabin air conditioner as well. Again, slight audio "stumble", then running OK.

After a few minutes, from the exhaust pipe I hear a "popping" sound that starts to become intermittent and the generator sounds like the engine is about to stall. Shut down the AC units and it appears to be running OK again. Last time I heard that "popping" was from my GM 8.1L Vortec motorhome engine and a replacement of spark plugs and ignition wires fixed the problem. The generator only has 204 hours, but I replaced the spark plugs anyway. See photo of replaced plugs. Note both center insulators are well blackened, but not fowled. Also, plug on left has its entire threaded area black and wet from fuel/oil?

Also, based on info I gathered from a YouTube video about Onan 5500 high oil level causing a stalling problem, similar to what I found, I removed about 1-1/2 pints of engine oil from the sump.

Generator seems to run just fine now with both AC units running at 23 amp load on generator and oil level about 1/4" up from the "Add" oil mark on the dipstick.

However, I think a carb flush with Seafoam and gas mix would be a good PM move, just in case.
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Old 04-26-2021, 12:28 AM   #11
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(geofferyh) re: " plug on left has its entire threaded area black and wet from fuel/oil?" SUGGESTS to me that the spark PLUG WAS LOOSE, thus allowing compression/ exhaust leakage up through the threads. IF the plug was sealed, there should be no carbon/gas on the threads. THIS ALONE can cause a miss/ stumble/ loss of spark, which in turn, dumps raw, unburned gas into the HOT exhaust, which causes the muffler backfire. 2) On oil level, it is critical that rig is LEVEL when OIL is changed, so that all oil drains and proper levels are reflected on the dipstick. LUCK to ya
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Old 05-13-2021, 08:58 PM   #12
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Ray, Re: "low oil shutdown feature"... does shut off running engine on il loss, when working properly... and can be one of two methods: 1) If Oil Filter used, a PRESSURE SWITCH kills IGN; 2) On models that do NOT use oil filter and use a FLOAT /SWITCH in the oil sump, still kills IGN
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Old 05-15-2021, 07:54 PM   #13
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TIP: Always make sure rig properly leveled BEFORE CHANGING GEN OIL, or dipstick readings can be meaningless :-)
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