Legend:
1 battery
2 ignition switch
3 coil
4 ignitor
5 magnetic pickup inside distributor
If you have a general interest in rotary ignition, go ahead and experiment with SLIDFIS on your own vehicle, but do so at your own risk. It should only be used in a temporary installation because DLIDFIS is what you really should be using. But if you're like me, you'll end up doing whatever you want anyway!
Here's how it all started:
I had read Paul Yaw's site and really wanted a direct fire ignition, but I couldn't afford an MSD at first, so I decided to try my luck with a non MSD direct fire ignition system by simply hooking up two coils to the Leading ignitor in my rotary truck. I used a very long hose clamp (size 104) and a small piece of radiator hose with a piece of sheet metal formed into a hook to support the extra coil. After the hose clamp was tight I tried to move the coil and it felt tight enough. It would be good enough for a more or less permanent installation because I planned on getting an MSD anyway.
The wiring to the Trailing coil remained unchanged and still ran through the distributor cap like before, but I reasoned it would be better to run it through the Leading contacts instead of the Trailing contacts. The Leading contacts have a carbon button and only one gap to jump compared to the two gaps of the Trailing contacts (look under the cap and study it and the rotor of any '74 to '85 distributor and you will see what I mean).
I wasn't sure if the stock ignitor could spark two coils, especialy when Paul Yaw himself didn't know if the MSD 6A could spark two (as stated in his article). Note: I found out that the MSD's CD output is not good to hook in parallel to two coils as per Yaw's instructions. It lowers the amperage going to the coils. Well, it will work for you if it's what you want to use, but it isn't the best you could do for your engine.
Anyway, I made two jumper wires to hook both Leading coils in parallel. I hooked the (+) and (-) of one coil to the same terminals of the other coil. I then ran a plug wire from each coil down to the Leading plugs (it doesn't matter which one). This is the same way that the MSD and DLIDFIS are hooked up, well from the coils to the plugs at least.
I double checked my wiring and cranked the engine. It took a few seconds longer to start and the moment it finally fired, there was a small backfire, but it ran smoother and sounded a lot like a second gen RX-7!!!! Now I know why rotary trucks and other older rotary cars sound different than the newer ones! I drove it around the block and noticed that I had a little more power than I used to have (even with the engine as cold as it was). All the good things about direct fire that you would expect were embodied in my truck. I drove back home and hooked up my inductive timing light to see my current timing setting and right as I hit the trigger, I noticed a bad stumble in the idle. It was weird. The engine RPM started to get really low as if it was going to die, so I reved it a little and the miss went away. It started running better. Direct fire was firing both coils at the same time so I could see the timing mark even when the timing light was on the rear rotor (L2).
I moved the timing light to the front rotor and as soon as I hit the trigger, it started missing and almost dying again! What is going on? Anyway I reved it up a bit and it settled down again. The timing mark was flashing good again at that point so I switched back to the rear rotor and it started missing really badly again. The timing light really showed the missing, especialy on the rear rotor. The front seemed to miss less when the inductive clamp was hooked to it. I tried to take my truck for a second test drive and it died in my driveway. It again took longer to start than normal and began with another backfire. It ran terrible. As I was driving, I reved it up to 6 grand in first and wasn't impressed. The secondaries didn't even open.. or maybe I didn't feel them as the engine was running so rough. I made it back home, but it was running quite badly. The engine had very little power, it idled extremely rough, it would die easily, even the tailgate was rattling.
Hmm, why did it start running so badly? Did I burn out the ignitor? Did I fry my coils? Were my plugs simply fouled? To answer that last question I removed the plugs and looked at them. They were rather clean (just a little bit of carbon). I wire brushed them and reinstalled them. The engine still had no improvement.
Now I suspect a few things are going on here....
1) it ran better when cold... maybe the choke helped create a vacumm of sorts in the spark plug area and was therefore easier to fire when cold with less presure.
2)I'm pretty sure the stock ignitor was never meant to fire more than one coil. The available amps are reduced by at least 50% with two coils sharing the same ignitor.
3)Maybe if I hooked up a second ignitor to the same trigger I could run two coils without as much of an amperage loss. (well duh! this is what DLIDFIS is all about, and it works better than yo mama!)
5)Maybe my alternator is bad and my battery was getting drained by the 3 coils and was continously running worse as the available battery power was draining (I doubt it).
6)It never backfired when starting before the direct fire, but I understand that the wasted spark fires into the exhaust phase so maybe it's showing me that there is an exhaust leak. I wouldn't be suprised since the header is quite old.(DLIDFIS has prevented all backfires since installing it!)
I simply gave up on it and wrote Paul Yaw an email explaining my project and asking advice. He replied and suggested running the two coils in series. He said I was likely overloading the ignitor.
In series huh? Well I didn't really understand at the time, but I went ahead and ran the yellow-blue (-) wire from the ignitor to the (-) terminal of the first coil, and hooked the (+) terminal of the first coil to the (-) terminal of the second coil, then hooked the (+) terminal of the second coil to the (+) wires from the ignitor/key switch. It worked extremely well! No more weird backfires or fouling plugs, even when fully warmed up! The timing light was rock-solid!
It started easier and the sound of the engine had changed a little. It sounded like the idle was higher than what the tach was actually showing (tach is hooked to Trailing coil as usual). I had to double check how far out the choke was pulled to make sure. It looked like it was at a good spot, but the tach still seemed to read a little off. The idle was around 1050 to 1100RPM compared to the norm of 950 to 1000 (it must have been easier for the engine to idle with more sparks, hence the slightly higher rpm). The idle was smoother, it had more power going up a hill near my house, and it still sounded like a second gen RX-7.
So Yaw's MSD system is hooked up to the coils in parallel, and the single Leading ignitor direct fire ignition system is hooked up in series. Fair enough. By the way, DLIDFIS uses two ignitors and two coils on Leading (each ignitor is hooked to a single coil), so the series/parallel argument doesn't even apply here. You can also hook two MSD boxes to single Leading coils so each one delivers full power (similar to DLIDFIS). This gets around the low amperage CD spark problem, but is way more expensive and takes up more room under the hood.
I may eventually do my own pic/explanation like they did, but for now, check out the links above.
By the way, I am going to try my MSD 6AL in my baja when I get an engine for it (boinger).