Home » Public Forums » GMCnet » Onan troubleshoot (Onan running rough)
| Onan troubleshoot [message #368803] |
Thu, 17 February 2022 10:59  |
Ken Shaffer
Messages: 89
Registered: September 2017
Location: Marion Iowa
Karma: -1
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can anyone help me with my Onan 6k? It ran perfectly 2 years ago. It slowly starting running rough. Now it will start and run on a low RPM for maybe 5 minutes. After that it becomes really rough and eventually quits. I have done the following and nothing has changed. It still acts the same as it did.
replaced spark plugs, fuel pump, converted to Bovee's electronic ignition, rebuilt carburetor. I had previously installed Dinosaur board.
I notice that the front cylinder seems to have a stronger spark than the rear.
My next plan is to change plug wires and coil.
I am running out of ideas. (and new parts to throw at it)
Has anyone had a similar problem and can share your experience with me?
Ken Shaffer
Marion Iowa
73 Canyon Lands, 455, Micro-level, Alum radiator, Alcoa wheels, Lenzi hubs/bearings, Howell EFI/EBL, Rostra Cruise, Custom interior
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| [GMCnet] Re: Onan troubleshoot [message #368805 is a reply to message #368803] |
Thu, 17 February 2022 11:15  |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Pinched/collapsed fuel line? zPull drawer out and see if problem continues.
Mac in OKC, OK
Sent from my iPhone
On Feb 17, 2022, at 10:59, Ken Shaffer wrote:
can anyone help me with my Onan 6k? It ran perfectly 2 years ago. It slowly starting running rough. Now it will start and run on a low RPM for
maybe 5 minutes. After that it becomes really rough and eventually quits. I have done the following and nothing has changed. It still acts the same
as it did.
replaced spark plugs, fuel pump, converted to Bovee's electronic ignition, rebuilt carburetor. I had previously installed Dinosaur board.
I notice that the front cylinder seems to have a stronger spark than the rear.
My next plan is to change plug wires and coil.
I am running out of ideas. (and new parts to throw at it)
Has anyone had a similar problem and can share your experience with me?
--
Ken Shaffer
Marion Iowa
73 Canyon Lands, 455, Micro-level, Alum radiator, Alcoa wheels, Lenzi hubs/bearings, Howell EFI/EBL, Rostra Cruise, Custom interior
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| [GMCnet] Re: Onan troubleshoot [message #368806 is a reply to message #368803] |
Thu, 17 February 2022 11:12 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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Ken,
You need Duane Simmons' onan troubleshooting guide. Someone more web savvy
here should post a link for you soon.
Have you tried running the genny with a temporary gravity feed fuel tank in
order to rule out fuel delivery?
Sully
Bellevue wa
On Thu, Feb 17, 2022 at 8:59 AM Ken Shaffer wrote:
> can anyone help me with my Onan 6k? It ran perfectly 2 years ago. It
> slowly starting running rough. Now it will start and run on a low RPM for
> maybe 5 minutes. After that it becomes really rough and eventually
> quits. I have done the following and nothing has changed. It still acts
> the same
> as it did.
>
> replaced spark plugs, fuel pump, converted to Bovee's electronic ignition,
> rebuilt carburetor. I had previously installed Dinosaur board.
> I notice that the front cylinder seems to have a stronger spark than the
> rear.
> My next plan is to change plug wires and coil.
> I am running out of ideas. (and new parts to throw at it)
> Has anyone had a similar problem and can share your experience with me?
>
> --
> Ken Shaffer
> Marion Iowa
> 73 Canyon Lands, 455, Micro-level, Alum radiator, Alcoa wheels, Lenzi
> hubs/bearings, Howell EFI/EBL, Rostra Cruise, Custom interior
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| [GMCnet] Re: Onan troubleshoot [message #368807 is a reply to message #368805] |
Thu, 17 February 2022 11:38 |
Ken Shaffer
Messages: 89
Registered: September 2017
Location: Marion Iowa
Karma: -1
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Member |
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I did replace the fuel pump but I did not pull out of a separate tank. I
will try that to make sure the fuel line is not pinched between pump and
fuel tank. Good idea, thanks!
On Thu, Feb 17, 2022 at 11:15 AM K2GKK D C_Mac_ Macdonald
wrote:
> Pinched/collapsed fuel line? zPull drawer out and see if problem
> continues.
>
> Mac in OKC, OK
>
> Sent from my iPhone
>
> On Feb 17, 2022, at 10:59, Ken Shaffer wrote:
>
> can anyone help me with my Onan 6k? It ran perfectly 2 years ago. It
> slowly starting running rough. Now it will start and run on a low RPM for
> maybe 5 minutes. After that it becomes really rough and eventually
> quits. I have done the following and nothing has changed. It still acts
> the same
> as it did.
>
> replaced spark plugs, fuel pump, converted to Bovee's electronic ignition,
> rebuilt carburetor. I had previously installed Dinosaur board.
> I notice that the front cylinder seems to have a stronger spark than the
> rear.
> My next plan is to change plug wires and coil.
> I am running out of ideas. (and new parts to throw at it)
> Has anyone had a similar problem and can share your experience with me?
>
> --
> Ken Shaffer
> Marion Iowa
> 73 Canyon Lands, 455, Micro-level, Alum radiator, Alcoa wheels, Lenzi
> hubs/bearings, Howell EFI/EBL, Rostra Cruise, Custom interior
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
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Unsubscribe or Change List Options:
Ken Shaffer
Marion Iowa
73 Canyon Lands, 455, Micro-level, Alum radiator, Alcoa wheels, Lenzi hubs/bearings, Howell EFI/EBL, Rostra Cruise, Custom interior
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| Re: Onan troubleshoot [message #368810 is a reply to message #368803] |
Thu, 17 February 2022 15:24 |
boybach
Messages: 566
Registered: December 2020
Location: Vancouver Island
Karma: 4
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How much gas have you got in the Motorhome? The genny will quit long before you run out of gas.
Larry
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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| Re: Onan troubleshoot [message #368814 is a reply to message #368803] |
Thu, 17 February 2022 21:22 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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“One plug having a better spark than other” is a red flag. The plugs are in series since waste spark ign so they should be the same. It goes coil tower-wire- plug-block-other plug-other wire-other coil terminal for each spark event. Check both plug gaps at .020. Then on bench meter them. Be sure no reading from terminal to body. Then check series resistance terminal to center electrode. Both plugs should have a similar internal resistor value. Plug QC isn’t what it used to be and I now precheck all before install. If there is any resistance value terminal to body the spark energy with go though that route instead of air gap as takes easier path. The other plug would have a better spark as the shunted one would behave as a pass through.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Onan troubleshoot [message #368815 is a reply to message #368803] |
Thu, 17 February 2022 22:56 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Decarbonize the heads / cylinders. It is suppose to be done every 200 hours.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Onan troubleshoot [message #368817 is a reply to message #368814] |
Fri, 18 February 2022 06:54 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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JohnL455 wrote on Thu, 17 February 2022 22:22“One plug having a better spark than other” is a red flag. The plugs are in series since waste spark ign so they should be the same..
I will point out that it is entirely likely to see a difference between the plugs from a wear perspective. The discharge energy from the coil is DC - and the plugs are in series as John pointed out - therefore one plug always fires electrode positive and other always fires electrode negative. This results in a different amount of heat generated across each gap and thus a differing level of arc erosion over time - the plug in one cylinder will always be producing a "hotter" spark than the plug in the other cylinder. An analogy is from welding where you will get significantly different electrode heating from running DCEP versus DCEN.
As for one plug having a "better spark than the other"....I don't see how you can determine that with an ionization-type spark tester on a wasted spark system.
If it were me I'd be ruling out fuel problems before going after ignition issues based on the original problem description...but hey, what do I know...
--Jim N8ECI
Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: Onan troubleshoot [message #368820 is a reply to message #368803] |
Fri, 18 February 2022 08:54 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Great insight Jim. Makes sense. Wanted to be sure he understood the system, and check plugs and gaps as no cost quick thing to rule out. To take it further to rule out the plugs after the Ohm test and gap check, swap their positions and sparks should appear same in that position for as much as you can tell.
My experience with poor off shore Champion plugs was this. My high mile Jeep would occasionally cold start with one dead cyl, then clear with a rev. It was also always slightly low on coolant. Logic pointed to a head gasket, Finally it got bad enough to set a cyl 2 misfire and pulling the 1 year old plugs found cyl 2 to have an internal short not visible to the eye. The low coolant was a bad cap (recently replaced but defective). So don’t assume recently replaced parts are good. Been 6 months and no misfires. There is a pretty inconsistent internal resistor variance plug to plug on brand new plugs. Copper plugs are cheap, so ones that are way off scale don’t get installed by me. Normal wide variance of say 20% gets a pass.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Onan troubleshoot [message #368826 is a reply to message #368820] |
Fri, 18 February 2022 12:43 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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To reinforce Jim Miller's comment. I always swap the plug positions if I ever have plugs both out at the same time. I do this even if the Onan is running fine. I also check the gaps and make sure that they are exactly the same and correct. This series wired wasted spark system used on 2 cylinder engines can produce some interesting failures that you would not see on other systems.
De-carbonize the heads / cylinders.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Onan troubleshoot [message #368830 is a reply to message #368803] |
Fri, 18 February 2022 18:05 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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The appliance repair tech once said not to use the self cleaning feature if you want your equip to last. I’m going to try some John Deere foaming glass cleaner and see how that does.
On the Onan carb, did you ((breaker off) hold the throttle closed down to abot 500 RPM and adjust the idle mixture screw to best idle speed holding throttle closed? Then release throttle and set main jet no load and load? Rmember these are garden tractor engines (JD318) and were meant to throttle from idle to 3600 run speed. Ours are stuck at 1800 which in my opinion uses both carb circuits to some degree especially no load.
John Lebetski
Woodstock, IL
77 Eleganza II
[Updated on: Fri, 18 February 2022 18:08] Report message to a moderator |
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| [GMCnet] Re: Onan troubleshoot [message #368831 is a reply to message #368830] |
Fri, 18 February 2022 18:15 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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If you do the idle adjust bit, be darned sure that your generator is NOT
SUPPLYING POWER AT THIS TIME! What ever you might be powering at the time
ain't gonna like it, even a little bit. But, if you look at the throttle
position when the engine is cranking, you will notice that it is wide open,
not at idle. The governor spring is holding the throttle wide open until
the effort from the governor arm balances the effort of the spring. Jus'
sayin'..
Jim Hupy
Salem, Oregon
On Fri, Feb 18, 2022, 4:06 PM John R. Lebetski
wrote:
> The appliance repair tech once said not to use the self cleaning feature
> if you want you equip to last. I’m going to try some John Deere foaming
> glass cleaner and see how that does.
> On the Onan carb, did you ((breaker off) hold the throttle closed down to
> abot 500 RPM and adjust the idle mixture screw to best idle speed holding
> throttle closed? Then release throttle and set main jet no load and
> load? Rmember these are garden tractor engines (JD328) and were meant to
> throttle from idle to 3600 run speed. Ours are stick at 1800 which in my
> opinion uses both carb circuits to some degree especially no load.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
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| [GMCnet] Re: Onan troubleshoot [message #368838 is a reply to message #368834] |
Sat, 19 February 2022 11:21 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Keep in mind that the gap on thes units are only .020, not .35.
Realize your using the Pertronic kit, which can handle .35.
Also the Ignition wire on the original need to be changed after 45 years.
On Sat, Feb 19, 2022 at 6:36 AM John R. Lebetski
wrote:
> Yes Jim, breaker OFF was in my procedure.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
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--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: Onan troubleshoot [message #368900 is a reply to message #368803] |
Fri, 25 February 2022 18:04 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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I'd pay attention to Jim Miller if I were you. To my limited experience you describe a fuel problem.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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