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jazzman1009
post Oct 12 2012, 07:58 PM
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Hi all, I need some advice on a generator issue. I have an Onan Marquis Gold 5.5. It is having trouble running properly when placed under a load (AC, Water Heater, etc.). The problem never existed until recently. When placing a load on it, it would start to act like it wants to stall, RPM's go down, sputters, backfires, then seems to recover. After a couple of minutes, or sometimes sooner, it will do it again. Seems to clear up after it is running for awhile and is hot. Then another problem popped up with the thing not starting at all. I ended up replacing the carb and it starts right up, but the original running under a load problem is back. It was then suggested I was having a fuel pump problem, replaced that today to no avail. Has anyone experienced a similar problem with this model generator? I hate to keep throwing money at it and not having the problem solved. I am wondering if I just don't have a set of bad plugs? Again, it appears the problem goes away if it has run for quite sometime with no load. Any suggestions are appreciated!
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John Blue
post Oct 13 2012, 09:14 AM
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One item you need to think about is an (air leak) in the fuel line. If the fuel lines are on the old side and some tine ago were not set up to use the 10% ethanol fuel. Ethanol will eat up fuel filters and fuel lines if not the newer type. All filters and fuel lines have been changed out a couple years ago but some places may have the old stock on the shelf yet, you need to ask. The better supply house's replaced stock years ago.

We have a diesel Gen but it will work the same way as what you see. Run under no load but stall under load. Do this. Pick up a short amount of fuel line and bypass the main fuel tank. Set a 5 gal fuel can on the ground and feed the unit. If it runs under load with no problem you will need to replace the fuel line back to the fuel tank. Low cost test to run. Note: you will never see the cracks in the fuel line and no fuel will run out as point air is leaked in.


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John
Brandon, Fl.
FMCA F-248693
Foretravel MH
Honda CRV tow
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John Q Citizen
post Oct 14 2012, 03:23 PM
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QUOTE(jazzman1009 @ Oct 12 2012, 07:58 PM) *

Hi all, I need some advice on a generator issue. I have an Onan Marquis Gold 5.5. It is having trouble running properly when placed under a load (AC, Water Heater, etc.). The problem never existed until recently. When placing a load on it, it would start to act like it wants to stall, RPM's go down, sputters, backfires, then seems to recover. After a couple of minutes, or sometimes sooner, it will do it again. Seems to clear up after it is running for awhile and is hot. Then another problem popped up with the thing not starting at all. I ended up replacing the carb and it starts right up, but the original running under a load problem is back. It was then suggested I was having a fuel pump problem, replaced that today to no avail. Has anyone experienced a similar problem with this model generator? I hate to keep throwing money at it and not having the problem solved. I am wondering if I just don't have a set of bad plugs? Again, it appears the problem goes away if it has run for quite sometime with no load. Any suggestions are appreciated!


It sounds like your genset is having breathing problems. Have you used Onan Carburator cleaner per owner's manual. More important than cleaning the carburator, the cleaner removes carbon deposits from the combustion chamber. Just replacing the carburator will not help the combustion chamber breathe easier. Also check to see if your unit has a plug in the muffeler with which to purge accumulated carbon from the spark arrestor, which also can also plug up your system. Remove plug, run genset under full load, (AC[s], microwave etc.. as much as the genset will handle), for about 15 minutes, wait for muffeler to cool off, and reinsert the plug. If your genset is approaching 500 hrs, it is getting time for a major tuneup, where the techs will, among other things, remove the heads and manually scrape the carbon deposits out.
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jazzman1009
post Oct 15 2012, 01:32 PM
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Thank you for the suggestions. I will check into everything a little further. The generator has only about 90 hours on it. Like I stated, it runs perfectly until it sees a heavier load such as the air conditioner AND the water heater, or both air conditioners, etc. The thing used to run the entire RV with no issues. I also noticed when I changed out the fuel pump, the hardline going over to the RV gas tank moved real easy on me when I took the small rubber supply hose off the fuel filter. I did not give it much thought, but now I am wondering if there is a loose connection on the gas tank end. Any more suggestions definitely welcome! Will post again when/if I find the problem.
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