| Wasted Spark Design [message #134979] |
Sun, 17 July 2011 22:27  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I have worked an many wasted spark ignitions over the years mostly on 2 cylinder motorcycles and a few Onans. I thought I remembered how the coil was designed but now I'm doubting what I thought I knew. I know it is just a basic transformer with a single primary winding but it is the secondary I'm concerned about. I thought the secondary was one winding with a center tap to ground. I have a used replacement Onan coil in my hand and I'm not reading anything between the spark plug terminals (secondary) and ground (the case). I also looked up the wiring diagram and it does not show any center tap. If this is true then the spark plugs must fire in series using the engine ground as the cross connection between the plugs. If they do fire in series then my diagnostic procedure was flawed because I had both of them disconnected when I was trouble shooting this Onan problem.
Does anyone out there know how this coil is wired internally? Yes, I have read the diagnostic procedure in the Onan manual.
The other problem I have on this replacement coil is the secondary only measures 14.5k ohms. The book says it should be 40K ohms. I do not have to original here right now to measure it.
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Wasted Spark Design [message #134988 is a reply to message #134979] |
Sun, 17 July 2011 23:03  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Ken,
There is no center tap on the secondary. The cylinder not in
compression has low resistance so the spark across that plug
dissipates little energy -- looks like a short. The other cylinder,
under compression, has high resistance and dissipates most of the
spark energy, igniting the mixture.
Ken H.
On Sun, Jul 17, 2011 at 11:27 PM, Ken Burton wrote:
>
>
>... I have a used replacement Onan coil in my hand and I'm not reading anything between the spark plug terminals (secondary) and ground (the case). I also looked up the wiring diagram and it does not show any center tap. If this is true then the spark plugs must fire in series using the engine ground as the cross connection between the plugs. If they do fire in series then my diagnostic procedure was flawed because I had both of them disconnected when I was trouble shooting this Onan problem.
...
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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] Wasted Spark Design [message #134991 is a reply to message #134988] |
Mon, 18 July 2011 01:47 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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OK Ken. That is what I'm seeing. The two plugs are in series. I guess I'll go back and diagnose this thing all over again with this new knowledge. I swear somewhere I have seen a design with the center grounded. Maybe my memory if failing me but I'm sure I have seen this on a Honda or Yamaha.
You confirmed what I am seeing on the meter and what I have seen in the Onan manual. So as soon as it cools off I'll go back and try again. It was 98 here today so I did not do much outside work.
How is the back doing?
Thanks Ken
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Wasted Spark Design [message #134995 is a reply to message #134991] |
Mon, 18 July 2011 07:30 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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The Onan's the first lost-spark system I ever saw, so I was really
surprised "back when". :-)
Not a good time to ask about the back. :-( It's been tolerable for
the past week or so, but getting worse in preparation for tomorrow's
Dr. appt. Just finished my morning exercises which really exacerbated
it this time. This too shall pass. I hope. 'Cause I need to get
under the GMC.
Lost some transmission fluid on the way home yesterday -- to the point
that it wasn't on the dipstick & coach would hardly move. After
adding the two quarts I had with me, we made it the 50 miles home with
everything apparently OK. I think what happened was that I towed with
the toad brakes engaged for a while -- the dead man switch got
entangled with the tow bar and was tripped when I stopped about the
slipping 425. Since I have a prominent "Toad Brakes" dash light, I
can't imagine having missed it for long, but something caused the ATF
loss. Strangely, to me, most of the leakage was onto the starter and
that area -- can't figure where that can have come from. I didn't
check the overflow vent catch bottle.
Ken H.
On Mon, Jul 18, 2011 at 2:47 AM, Ken Burton wrote:
>
>
> OK Ken. That is what I'm seeing...
> How is the back doing?
>
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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: Wasted Spark Design [message #134997 is a reply to message #134979] |
Mon, 18 July 2011 07:52 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Ken Burton wrote on Sun, 17 July 2011 23:27 |
I have worked an many wasted spark ignitions over the years mostly on 2 cylinder motorcycles and a few Onans. I thought I remembered how the coil was designed but now I'm doubting what I thought I knew. I know it is just a basic transformer with a single primary winding but it is the secondary I'm concerned about. I thought the secondary was one winding with a center tap to ground. I have a used replacement Onan coil in my hand and I'm not reading anything between the spark plug terminals (secondary) and ground (the case). I also looked up the wiring diagram and it does not show any center tap. If this is true then the spark plugs must fire in series using the engine ground as the cross connection between the plugs. If they do fire in series then my diagnostic procedure was flawed because I had both of them disconnected when I was trouble shooting this Onan problem.
Does anyone out there know how this coil is wired internally? Yes, I have read the diagnostic procedure in the Onan manual.
The other problem I have on this replacement coil is the secondary only measures 14.5k ohms. The book says it should be 40K ohms. I do not have to original here right now to measure it.
Ken B.
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Ken,
You are not completely crazy....
One plug fires from each end of the secondary. Very common in two as a few four cylinder engines.
I did (in many years of messing with thing I should never have touched) run into a dual plug coil that actually had a dual winding for a secondary. (This was some weird-assed thing somewhere like a Richardo or a Kermath - old marine engines.) This was not a very successful system (IMHO).
The technical discussion in the manual was about how this avoided a "wrong polarity" on a "sparking plug". Though that may be an issue if you accept that the plugs are thermionic like a vacuum tube, I have not found that it makes a great difference. The problem with this dual coil was that if the plugs were not perfectly matched, the cross-over cylinder would eat all the spark energy wound up in the coil flux. (What a PITA to diagnose.)
When I finally got in touch with a fellow that knew and loved these engines (this was long prior to WWW). He recommend that I get two coils (this was a 4 cylinder) from some model of Harley Davidson (6V) and use those. He also said that I should carefully store the originals as they were a collector's item as most had been removed and thrown overboard.
Second note:
Back when I though it mattered, I did measure the DC resistance of many ignition coils. They vary widely among manufacturers. I seem to remember them as being between 10k and 50K(?). Only a true open or a ground to the case indicates failure. Very few have secondaries that are actually grounded to the coil shell. Most secondaries ground to the points side terminal.
When I had finally figured out what coils were truly preferred, along came true CD systems and the coil was now only a pulse transformer.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Wasted Spark Design [message #135004 is a reply to message #134979] |
Mon, 18 July 2011 09:18 |
Dennis S
Messages: 3046
Registered: November 2005
Karma: 2
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Senior Member |
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Ken,
My Maintenance manual says secondary resistance should read 14,000 (+/- 10%) Ohms.
Dennis
| Ken Burton wrote on Sun, 17 July 2011 22:27 |
I have worked an many wasted spark ignitions over the years mostly on 2 cylinder motorcycles and a few Onans. I thought I remembered how the coil was designed but now I'm doubting what I thought I knew. I know it is just a basic transformer with a single primary winding but it is the secondary I'm concerned about. I thought the secondary was one winding with a center tap to ground. I have a used replacement Onan coil in my hand and I'm not reading anything between the spark plug terminals (secondary) and ground (the case). I also looked up the wiring diagram and it does not show any center tap. If this is true then the spark plugs must fire in series using the engine ground as the cross connection between the plugs. If they do fire in series then my diagnostic procedure was flawed because I had both of them disconnected when I was trouble shooting this Onan problem.
Does anyone out there know how this coil is wired internally? Yes, I have read the diagnostic procedure in the Onan manual.
The other problem I have on this replacement coil is the secondary only measures 14.5k ohms. The book says it should be 40K ohms. I do not have to original here right now to measure it.
Ken B.
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Dennis S
73 Painted Desert 230
Memphis TN Metro
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| Re: Wasted Spark Design [message #135012 is a reply to message #135004] |
Mon, 18 July 2011 11:06 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Great. That matches what I have here. The manual I have is an older red covered one. I can tell by their timing recommendations. At least you have a manual that has a value that matches what I'm reading.
Thanks
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Wasted Spark Design [message #135132 is a reply to message #135004] |
Tue, 19 July 2011 02:57 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Dennis S wrote on Mon, 18 July 2011 09:18 |
Ken,
My Maintenance manual says secondary resistance should read 14,000 (+/- 10%) Ohms.
Dennis
| Ken Burton wrote on Sun, 17 July 2011 22:27 |
I have worked an many wasted spark ignitions over the years mostly on 2 cylinder motorcycles and a few Onans. I thought I remembered how the coil was designed but now I'm doubting what I thought I knew. I know it is just a basic transformer with a single primary winding but it is the secondary I'm concerned about. I thought the secondary was one winding with a center tap to ground. I have a used replacement Onan coil in my hand and I'm not reading anything between the spark plug terminals (secondary) and ground (the case). I also looked up the wiring diagram and it does not show any center tap. If this is true then the spark plugs must fire in series using the engine ground as the cross connection between the plugs. If they do fire in series then my diagnostic procedure was flawed because I had both of them disconnected when I was trouble shooting this Onan problem.
Does anyone out there know how this coil is wired internally? Yes, I have read the diagnostic procedure in the Onan manual.
The other problem I have on this replacement coil is the secondary only measures 14.5k ohms. The book says it should be 40K ohms. I do not have to original here right now to measure it.
Ken B.
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Well I was wrong. I went back today and re-read the book. Mine also says 14,000 ohms. I did not get to working on it today. It was 95 degrees and two different friends came up to me today saying their AC did not work in their cars. So I ended up working on AC systems. After that I was too hot to do anything else.
I picked up a couple of replacement plugs because I can not tell if either one of the ones I have is open. They are Platinum Bosh plugs and you can not get to the electrode with a meter probe.
For the heck of it I measured the internal resistor in the two new plugs and they were widely different. One was 28K and the other was 69K. I have no idea what is normal. I think I'll stop by the store tomorrow and meter another new one.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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