Home » Public Forums » GMCnet » New Onan STILL not right (Ignition problem too?)
| New Onan STILL not right [message #319944] |
Mon, 03 July 2017 23:07  |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
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From the old Thread (which has been split three times): "I think I'm getting to the bottom of this...finally."
The newest problem seems to be with the Onan Magna Arc electronic ignition. Symptoms are as follows:
After a successful test run under load for over an hour with a replacement fuel pump. it would not restart after I shut it down.
After checking the fuel pump function, I checked for spark and found no spark.
I hooked up the timing light and started adjusting the ignition module until I had a flash or two on the timing light.
I got lucky and got the adjustment correct and she fired right up.
After resetting the timing and adjusting the carb a little, I put a load (both Duo-Therm AC units)on it and it ran great.
After running it for an hour, I shut it down and it would not restart due to lack of spark again.
This whole scenario repeated it's self a few more times before I finally gave up (for now)
Is anyone here familiar with the Onan electronic ignition who could explain this behavior?
I hate to give up on a reasonably new ignition system, but if this is a problematic system, I'll give up on it and go with the Pertronix system.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: New Onan STILL not right [message #319945 is a reply to message #319944] |
Tue, 04 July 2017 06:40  |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
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Onan points are triggered by a push rod that rides on the cam which pushes the rod up to open the points. The rod may be binding in it's guide hole. This method of opening the points is a weak spot in an otherwise simple, reliable engine. Timing will wander based on the push.
The Onan electronic system does not change this method of triggering the firing of the ignition system. This is the big advantage of the Pertronix modification. When I had an Onan, I built an electronic ignition system that duplicated the expensive Onan method. It did improve the spark, but did nothing for the wandering timing.
Jim Miller (Mr. Onan) may have a solution. I defer to him.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] New Onan STILL not right [message #319947 is a reply to message #319944] |
Tue, 04 July 2017 07:35 |
Jim Miller
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Registered: March 2008
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On Jul 4, 2017, at 12:07 AM, Carl Stouffer wrote:
> After running it for an hour, I shut it down and it would not restart due to lack of spark again. This whole scenario repeated it's self a few more times before I finally gave up (for now) Is anyone here familiar with the Onan electronic ignition who could explain this behavior?
Hi Carl,
I haven’t worked directly with the Magna-arc product but from an image search it appears to be some sort of points/“pertronix" lashup where the contact points are replaced by a points-like rocker arm with a magnet or pole piece mounted on it that moves in front of a pertronix-like pickup.
There may be an electronic failure in the pickup device that is triggered by heat; when the unit is running the cooling air is sufficient to prevent the failure from occurring - but when the unit is run for a while and then shut down the heat coming up from the engine block activates the failure. As a basic test you can use freeze spray (or canned air with the can turned upside down) to give the pickup unit a chill - and then attempt to re-start it. If it restarts then you may have found your problem.
Additional searching shows that the magna-arc product is discontinued but may be available from Cummins/Onan dealers like JimK as a NOS part or perhaps from ebay or wherever. I would imagine whoever installed the magna-arc discarded the original breaker points so you can’t really go back to them as a quick test unfortunately. There is always the option of the Pertronix pickup mounted in the flywheel housing but that takes a little more work to install.
Jim Miller N8ECI
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] New Onan STILL not right [message #319948 is a reply to message #319945] |
Tue, 04 July 2017 07:46 |
Jim Miller
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On Jul 4, 2017, at 7:40 AM, Thomas Phipps wrote:
> When I had an Onan, I built an electronic ignition system that duplicated the expensive Onan method. It did improve the spark, but did nothing for the wandering timing.
Hi Tom,
As you have seen the cam-following pushrod method just doesn’t give enough resolution to get precise and repeatable timing regardless of whether the pushrod is triggering contact points or if it is activating some sort of electronic or VR pickup - however for the RV generator application super-precise timing doesn’t really matter IMO as long as one hasn't advanced the timing by some excessive amount that is just on the edge of causing detonation.
I think *any* electronic pickup is superior to breaker points/condenser from the standpoint of reliability. Points are notorious for pitting, getting dirty or becoming wet from condensation inside the points enclosure. Condensers go bad - which causes more pitting of the points - OR they go shorted which results in no spark at all.
The pertronix mounted in the flywheel enclosure gives an all-electronic solution that provides repeatable and reliable timing.
There’s also the solution of changing from a Kettering-type inductive ignition to a CDI type ignition and re-purposing the breaker points as the source of the timing signal to a CDI box. This approach gives a super hot spark (or multiple sparks!) and also eliminates the pitting and burning of the points because they are only providing a logic-level trigger to the CDI box. Timing will still be somewhat imprecise due to the limited resolution of the pushrod system but as I mentioned it doesn’t really matter in our application.
Just my $0.02!
—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] New Onan STILL not right [message #319949 is a reply to message #319947] |
Tue, 04 July 2017 07:46 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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Jim,
Your appraisal of the Onan electronic ignition is correct. 6-8 years ago
when I was considering making up a kit for the Pertronix upgrade, I talked
to Pertronix. They confirmed that the Onan system was, indeed, made by
them at Onan's request.
And interesting point from those discussions with Pertronix engineers:
They were concerned that with our intended application the duty cycle
would be excessive for their switching module. I never understood that
concern and the considerable empirical data the GMC community has
accumulated certainly disproves it.
IMHO, the flywheel-triggered Pertronix mod is the only sensible way to
ignite an Onan.
Ken H.
On Tue, Jul 4, 2017 at 8:35 AM, Jim Miller wrote:
> ...
>
> I haven’t worked directly with the Magna-arc product but from an image
> search it appears to be some sort of points/“pertronix" lashup where the
> contact points are replaced by a points-like rocker arm with a magnet or
> pole piece mounted on it that moves in front of a pertronix-like pickup.
> ...
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] New Onan STILL not right [message #319950 is a reply to message #319949] |
Tue, 04 July 2017 08:03 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Yes, Jim's description of the workings of the Onan Magna Arc system is spot on. The pick-up unit even looks like a Pertronix unit. I guIt certainly seems like the most logical solution to the problem. I can try cooling the pick-up unit, but all the symptoms point to a heat related failure.
Thanks everyone.
Oh, and happy Independence Day
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
[Updated on: Tue, 04 July 2017 08:09] Report message to a moderator |
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| Re: [GMCnet] New Onan STILL not right [message #319952 is a reply to message #319949] |
Tue, 04 July 2017 08:06 |
Jim Miller
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Registered: March 2008
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On Jul 4, 2017, at 8:46 AM, Ken Henderson wrote:
> And interesting point from those discussions with Pertronix engineers: They were concerned that with our intended application the duty cycle would be excessive for their switching module. I never understood that concern and the considerable empirical data the GMC community has accumulated certainly disproves it.
Hi Ken,
Thank you for sharing that information - it is very interesting. Like you, I do not understand their concern; the Pertronix was designed to replace breaker points in distributor systems - and in a distributor on a multi-cylinder engine it would be triggering far more often than it is doing in our Onan application.
—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] New Onan STILL not right [message #319954 is a reply to message #319952] |
Tue, 04 July 2017 08:54 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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Jim,
The only way I can rationalize the Pertronix concern is that the Onan, with
only one trigger per crank revolution leaves the switch ON more than a
multi-triggerr does. That would also explain why they suggested I use
their unit ffor the VW rather than the 1181 for an 8-cylinder. As it
turned out, the VW unit was less suited physically to the Onan. i've never
heard of anyone having an 1181 fail.
Ken H.
On Tue, Jul 4, 2017 at 9:06 AM, Jim Miller wrote:
> On Jul 4, 2017, at 8:46 AM, Ken Henderson wrote:
>
>> And interesting point from those discussions with Pertronix engineers:
> They were concerned that with our intended application the duty cycle would
> be excessive for their switching module. I never understood that concern
> and the considerable empirical data the GMC community has accumulated
> certainly disproves it.
>
> Hi Ken,
> Thank you for sharing that information - it is very interesting. Like you,
> I do not understand their concern; the Pertronix was designed to replace
> breaker points in distributor systems - and in a distributor on a
> multi-cylinder engine it would be triggering far more often than it is
> doing in our Onan application.
> —Jim
>
> Jim Miller
> 1977 Eleganza
> 1977 Royale
> Hamilton, OH
>
>
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: New Onan STILL not right [message #319957 is a reply to message #319944] |
Tue, 04 July 2017 10:09 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
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If I remember correctly, the Onan supplied electronic setup still uses the points, pushed by the pushrod. Just for the hell of it, I'd check the point gap and set it per their recommendations. You >might< have an easy heal.
--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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| Re: New Onan STILL not right [message #319958 is a reply to message #319957] |
Tue, 04 July 2017 12:24 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
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There are no points in this system. There is a 'lever' for lack of a better description, that wags back and fourth in front of the pick-up. The lever is actuated by the same push rod as would open and close the points.
I'll have to look at it again and see if there is an adjustment that puts the lever closer to the pick-up. I don't think it is adjustable, but I will check when I get a chance.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: New Onan STILL not right [message #319969 is a reply to message #319944] |
Tue, 04 July 2017 16:18 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
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OK. I'm not familiar with it, our old Onans had points and the new ones with electronic ignition had none. We didn't run any in between. Wonder, is the lever a Hall Effect probe or a reluctor or a photo system?
--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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| Re: [GMCnet] New Onan STILL not right [message #319990 is a reply to message #319971] |
Tue, 04 July 2017 22:31 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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I used a Velleman Electronic Transistor Ignition Kit # K2543. Price is about $25. Easy to assemble. Made my Onan run much better - hotter spark. However, by using the Onan original points as a trigger, still the problem of timing wander.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
[Updated on: Wed, 05 July 2017 12:20] Report message to a moderator |
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| Re: [GMCnet] New Onan STILL not right [message #320007 is a reply to message #319990] |
Wed, 05 July 2017 11:48 |
powerjon
Messages: 2446
Registered: January 2004
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Thomas,
The only Velleman kit I can find is the K2543 kit. The K2545 does not pop up on any of the searches that I have tried. If you have a link that would be appreciated.
JR Wright
> On Jul 4, 2017, at 11:31 PM, Thomas Phipps wrote:
>
> I used a Velleman Electronic Transistor Ignition Kit # K2545. Price is about $25. Easy to assemble. Made my Onan run much better - hotter spark.
> However, by using the Onan original points as a trigger, still the problem of timing wander.
> Tom, MS II
> --
> 1975 GMC Avion
> KA4CSG
>
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J.R. Wright
GMC GreatLaker
GMC Eastern States
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78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] New Onan STILL not right [message #320008 is a reply to message #320007] |
Wed, 05 July 2017 12:19 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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My early morning error - K2543 is correct. Thanks for catching it. I'll correct the original entry.
Tom, MS II w/Honda ev6010
2012 Phoenix Cruiser model 2552
KA4CSG
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