Rear cylincer not firing
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Novice
Joined: Oct 2009
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Rear cylincer not firing
Only been riding my first bike an 87 FXRS Lowrider for 6 months. Rear cylinder stopped firing. Followed the manual troubleshooting procedures and they pointed to the coils which are Dyna Coil dual plug single fire. I swapped them (wiring and all) and the "bad" coil still fired the front cylinder. The plug in the rear cylinder is not firing, there is no current passing through the plug wires to the rear. There is 12.3v-14.15v going to the coil depending on which of the wires I test going to the coil and the jumper is good. If any one can help I would greatly appreciate it. I gotta get back on the road!
Road Master
Joined: Aug 2008
Posts: 1,246
Likes: 251
From: Belle River Ontario
It sounds like there is a bad wire somewhere. It could be as simple as a bad plug wire. If the coil is working fine, then the problem is in the wiring going to the coil. I would look for a loose or corroded wire. With a single fire system you have two coils, one for each cyl. They should have lead wires going to them. At the end of the day you may need to go over the whole system from the points cover to the ignition moduel.
Hope this helps, wiring is a bitch...
Hope this helps, wiring is a bitch...
Elite HDF Member
Joined: Sep 2007
Posts: 4,468
Likes: 12
From: Bluffton, South Carolina
You have two wires going to each coil. one is power (12V) and the other is the impulse from the ignition. Perhaps the impulse wire is bad or the ignition is failing. Hope this helps.
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Novice
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Definatly an electrical issue
Yes there are 2 wires coming in to each coil and a jumper between the two coils and I have tested and comfirmed that each wire coming in has between 12.4v-14.5v, when running off the front cylinder, and the jumper is good. I also tested between the box behind the timing cover with the LED and the coils and I have continuity between every where it should be. Do you know how I test the pulse comming in to the coil controling the rear cylinder? Could I have a timing issue? Could I have a bad timing senser even though I have power going to the coil? It is an electro magnetic pick up (so to speek) being read by the revolution of the engine right? IE the "Pulse" you are refuring to.
HDF Community Team
Joined: Dec 2005
Posts: 5,422
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From: NC USA
We don't know what module you're running and they have different settings (and personalities) but try removing the pulse wire from the coil going to the rear and jump the pulse wire for the front cylinder to it. That will make it a dual fire (both coils fire every stroke) and see if you get spark then. If you do, that would point to the module being the culprit. You get into resistance/ohm/load issues and probably shouldn't run it like that for any time other test pusposes.
Elite HDF Member
Joined: Sep 2007
Posts: 4,468
Likes: 12
From: Bluffton, South Carolina
The jumper wire iss the 12 V ignition wire, it should be switched and go on and off with the ignition and kill switch. the other wire would be the inpulse from the ignition. The modules do go bad, we had one that was firing but no advance to the rear cylinder. We noticed it when we had the bike on the dyno, HPand torque was down and one cylinder had a perfect A/F ratio and the other was way off. This should be impossible with an EVO style manifold. so we checked the advance in both cylinders and viola there it was.
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Novice
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Connected the jumper and tested the the plug wires with one of those high speed RPM pulse testers and an automotive meter and they all tested good. So you were right. The module is bad thanks guys for the advice you saved me a lot of time and money.
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Cruiser
Joined: Aug 2007
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From:
I am having a similar issue. Started about a week ago, I will be riding along and power drops, like it is running on one cylinder only. I thought it was bad plugs (15000 mies) Put in new plugs, and still experiencing the same problem. I am running the original ignition system (with a new coil, wires etc)
I am guessing that after nearly 25 years, 63000 miles that my ignition may be starting to get flaky.
I am guessing that after nearly 25 years, 63000 miles that my ignition may be starting to get flaky.
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