View Full Version : Only Firing On Rear Cylinder

03-21-2007, 04:38 AM
Hey Guys,

I need some help here as I am totally perplexed. I have a '99 Softail that I am running a Dyna 2000 ignition w their DC-6 coil in dual fire mode. The old module burned up on me and I installed the new 1. Only problem is the bike is only firing on the rear cylinder. Checked coil (good) Plugs(good) but again no fire on front cylinder. Any ideas on what the problem might be? I am running a Thunderheart EHC on the bike and no diagnostic lights are lit. Any help you could provide would be greatly appreciated.

03-21-2007, 05:12 AM
there should be instructions on how to set the dip switches with it- it might be in single fire mode....


03-21-2007, 06:27 AM

Thanks for the advice, but the dips are set correctly to the dual fire mode. I thought this might have been the case as well. Double checked and they are set correctly.


03-21-2007, 08:52 AM
Had something similar to that happen to me. Just because you bought a new ignition doesn't mean you got a good ignition. I replaced my coil with a new one(ran like shit) done all i knew to do. I took it back to the shop where I bought it and come to find out it was a bad coil. Got a different one and it worked fine.

03-21-2007, 09:26 AM
Dual fire and only one cylinder firing, do both plugs spark? If you switch the plug wires does the other cylinder now fire? If it does, bad coil most likely. If same cylinder fires, might be bad ignition or mechanical problem in front cylinder, valve sticking, lifters etc.

03-21-2007, 12:12 PM
Thanks for the Advice guys. Springer, I did just that (switched plug wires) and the front now fires and not the rear. This being said, I had another Dyna coil sitting around and hooked it up. Same thing, firing rear but not front. Is it possible I might have a wire rubbed thru somewhere coming from the coil to the ignition module? I guess it is possible the second coil is bad also. Again, thanks for all the help guys it's really appreciated

03-21-2007, 07:15 PM
have you ohmed out the high tension leads (plug wures) themselves? from the coil tower end to the plug end s/b @1500-3000 ohms.....


03-21-2007, 08:53 PM
If you switch the plug wires and now the front cylinder fires ... have you replaced the plug wires? Does the coil have 2 or 3 terminals for wires from the ignition module?

I would tend to doubt 2 bad coils doing the same exact thing.

03-22-2007, 08:52 AM
Junior, Springer, Gambler,

Thanks for all the advice and I wanted to let you know I found the problem. Seems there must have been a burr inside the frame which sliced one of the coil wires. Did an Ohm check and no continuity so figured I had a break somewhere. It entailed me pulling half my wiring harness out of the backbone, but hey that's the way it goes sometimes. Thanks again for the help guys as I was definitely drawing off your knowledge. Makes me feel good to know I wasn't too far off base with my assumptions and my troubleshooting. Look forward to talking with you guys again.



03-22-2007, 09:06 AM
glad we could help and it worked out for you...

ride safe!


03-24-2007, 10:47 AM
Any time my friend. Who knows might be me the next time.

03-24-2007, 07:25 PM
Regarding single fire vs. dual fire, I found this interesting

Q: What about ignitions?

First a few terms:
•Single Fire - Spark plugs fire independently and only at the correct time. "Unfortunately, CCI (Custom Chrome Inc.) has taken it upon themselves to reverse the definitions of dual and single fire when referring to their proprietary Rev-Tech ignition products. Rev-Tech dual fire systems are really single fire systems, and vice versa.

•Dual Fire - In the stock HD ignition system (pre-1999), both spark plugs fire at the same time, so one plug is firing when it's piston is at BTDC of it's compression stroke while the other cylinder is also firing on its exhaust stroke, "wasting" a spark and igniting unspent gases. This causes a noticeable and unnecessary vibration and makes for harder starting. As of the 1999 model year, all stock H-Ds bigtwins have gone to single fire.

•Dual Plug - this is a popular Shovelhead modification but I have also seen it in Evos, a second spark plug is installed in each head, on the side opposite the stock plug. This is a total waste of time as you are only covering up an inefficient combustion problem.

•Rev Limiter - The ignition retards the timing at a preset RPM to prevent the motor from revving higher than desired. This is a Good Thing, as high revs will prematurely wear a motor and very high revs will find you saying interesting phrases like "Oh fuck, what was that !?!" and "Who do I know with a pickup truck".

Single-fire will not provide more HP but will give better idle and better throttle response off idle to 3K RPM. A hotter coil is also a must for these mods.

I have installed many different ignition systems and there is very little difference between most.
As far as overall performance, reliability and ease of installation, I would have to say that I like the Crane HI-4 Single Fire system the best.