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Old 03-25-2023, 11:13 AM   #1
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Onan 4000 Exhaust Problem

Hello group. The Onan 4000 on my 2017 Forester has been extremely loud lately. Today I covered the exhaust pipe with my hand and there is no pressure and no change in sound. There is absolutely no exhaust coming out of it. I got underneath and looked at the exhaust pipe and there is no damage. I removed the exhaust pipe and checked for obstructions but found none. I cranked it with the pipe off and covered the hole from the muffler(?) and there is no exhaust coming out. Exhaust is coming out from somewhere inside the housing. Any ideas what the issue might be and what I need to do to fix it?

Thanks
Mark
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Old 03-25-2023, 12:56 PM   #2
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Originally Posted by CampClark View Post
Hello group. The Onan 4000 on my 2017 Forester has been extremely loud lately. Today I covered the exhaust pipe with my hand and there is no pressure and no change in sound. There is absolutely no exhaust coming out of it. I got underneath and looked at the exhaust pipe and there is no damage. I removed the exhaust pipe and checked for obstructions but found none. I cranked it with the pipe off and covered the hole from the muffler(?) and there is no exhaust coming out. Exhaust is coming out from somewhere inside the housing. Any ideas what the issue might be and what I need to do to fix it?

Thanks
Mark
Pipe between cylinder head and muffler may have come loose at cylinder head. Often fastened with a couple of bolts holding flange tight to exhaust port.
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Old 03-25-2023, 05:33 PM   #3
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Will the generator have to be removed from the motorhome to do this?
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Old 03-25-2023, 05:45 PM   #4
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Will the generator have to be removed from the motorhome to do this?
It's been a long time since I worked on an Onan generator (sometime in the '80s) but I do recall everything is extremely "tight" and hard to get to beyond just regular maintenance.

See if you can follow the header pipe from muffler up to cylinder head. Logically this pipe won't be all that buried int he "cabinet" and may be accessible from below.

One concern I would have is that the connection or pipe itself is broken from any one of several causes, most common ruinning over or backing into something solid. Pipe broken from flange, studs/bolts broken, etc.

Should be able to at least inspect visually to determine next steps.
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Old 03-25-2023, 07:25 PM   #5
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Picture is from a KY series Spec K of the ~~ 2003 vintage.

An exhaust leak could be from either the red arrow (flex tube) or the green arrow (muffler/gasket joint.)

With any luck it could be just a couple of loose bolts. Either way access will be more of a problemÖ
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