strange ignition experiment

[clarence]

Hi ,I did something on a whim recently.
My tci crapped itself finally, and a s/h one from ebay didn't work either so I had an idea.
I had some bosch hei modules [bim024] lying about and thought what the heck, maybe it will run extremely advanced without a timing curve, but I just wanted to have a ride. It had been months. So I hooked them up and pop bang splutter but would not run for more than a couple of secs. I checked the wiring and each pickup and coil were wired correctly. Then I increased the resistance from the pickups to approx 500 ohms using a potentiometer and could get it to idle but would die with the slightest throttle. So I reversed the polarity of the pickups and but not much change.

Now here is where things get really strange. During my experiments I accidently switched the pickup wires. ie front cylinder pickup was firing rear cylinder and vis versa.
It started right up and seemed to run fine and idle very smoothly. So I took it for a spin. The power is noticeably lessened but is still rideable. cruised on 100 kmph no problems.

Maybe the cylinders are now firing on the wasted spark cycle from their incorrect pickups? I have no idea but at least I got my ride.

Probably not wise to keep riding it like this, but as an emergency it's a simple cheap workaround.
I have some programmable timing curve kits that I intend to put together one of these days , and maybe incorporate them with the hei modules

cheers.

[Jimustanguitar]

Very interesting.

I know that some of the inline twins fire both plugs at both times. The cylinders are truly 2 cycles apart and it doesn't hurt anything to fire a plug a few degrees BTDC on the exhaust stroke.

It's been discussed before, and I'm certain that this isn't the case on V engines. The firing sequence wouldn't line up that conveniently, so something else is going on in your experiment.

Keep testing, your ignition kit sounds very interesting!

[Rikugun]

Now here is where things get really strange. During my experiments I accidently switched the pickup wires. ie front cylinder pickup was firing rear cylinder and vis versa.
It started right up and seemed to run fine and idle very smoothly.

Are you certain they were switched? Is there any way to confirm with a timing light? Provided the timing isn't too far off the front and or rear flywheel marks may be visible. Compare which is illuminated when the timing light is attached to each cylinder's plug lead.

This gentleman made an igniter substitute using GM HEI modules. It's for an application that has a mechanical advance but his insight regarding the electronics end of things may help shed some light.

http://home.comcast.net/~loudgpz/GPZweb/Ignition/GPZgmHEImod.html

If you click on the home page link there's another article for a different kind of homemade igniter although more complicated than the HEI version.

[clarence]

yeah, it's been bugging me. Red pickup wire is for front cylinder right? I am going to double check today. I will take a pic of the whole shamozzle and upload it here when I can find time. also the tach goes bouncing all over the place at times, so maybe a bit of crosstalk is happening too.

[clarence]

ok I am fairly sure the pickups are reversed. if this tci_diagram  pic is correct

[Rikugun]

And the ignition coils' wires haven't also been inadvertently swapped?

This does sound strange although I have no idea what effect the incompatibility of the components has. I have to imagine it is advancing or delaying the coil's firing to work. Is your hypothesis it's running on what would be the wasted spark from the "wrong" coil? (or is it the right coil timed wrong!?) If so it seems like it would be at least 70 degrees off at idle - again assuming all things being equal. Which there not.  :)

I'll have to look at the firing pulse diagram later to even begin to wrap my head around this. Even then it seems like an academic exercise at best. I can't imagine the bike is running all that well or retains it's intended performance with no advance feature.

[clarence]

ya it's confusing the hell out of me too. I took it for a 50 km ride yesterday. The power is down I would say 25% . It feels more retarded than advanced. Starts really easily and idles very smooth, but quieter and weaker if that makes sense?

During my initial experiments when the pickup wires were correctly connected it was obviously too far advanced as you would expect. On a couple of trials when I got it to rev over 2000 rpm it took off and I could redline it, and it felt fully responsive like with a normal tci, but was nearly impossible to start and keep running unless I could keep the revs over 2000.

I don't know about the wasted spark hypothesis, that's just a guess. Someone on this forum may be able to figure out what's going on :o

[clarence]

Ok I think I know what might be happening.

If we estimate the pickups being 30 degrees apart from each other and each pickup factory set to fire at 35 degrees btdc then when the pickups are reversed, one of  the pickups will trigger at 5 degrees btdc and ignite eg front cylinder on compression stroke. The other pickup by sheer chance happens to trigger the rear cylinder at somewhere close to tdc on it's wasted spark cycle.

So only 1 cylinder is firing on wasted spark.
It's the only plausible thing I can think of atm.

[Rikugun]

If I'm not mistaken the pickup coils are spaced the same 70 degrees as the engine V. Assuming the modules are good and connected same way, same resistors added, etc., the coils may still fire 70 degrees apart but when is in question. There may be ways to determine what the current timing is if you were so inclined to continue your experiment.

Given the engine starts easily and is a bit sluggish performance wise I'd agree it's retarded. I'm guessing fuel economy has dropped off. Since combustion is no longer confined in the chamber where it belongs, certain engine damage can result from continued operation. The severity and how quickly it occurs depends on just how retarded the timing is.

The HEI's look used. Are they known to be good and act the same? Do they require a heat dissipating gel between them and the heat sink?

[clarence]

The pickups probably are 70 degrees apart. the 30 was just a guess for for my thought experiment, which is probably bunk :o
The modules are used, but came from working cars, 1980's ford falcons [australia]. Also I am not using any ballast resistors on the coils. The hei modules have a built in dwell circuit too. Yes there is heat transfer paste. That tan colored plate is aluminium. The modules barely get warm. possibly because they are triggering only once per revolution compared to 3 with the original six tooth reluctor. Although the vision is revving twice as hard as the ford for the same speed , the ford will still trigger more. My brain is about to explode. :P
The original reluctor wheels that trigger these modules have very small teeth, whereas the visions flywheel magnet is quite long looking at the pics on the web, so it's amazing it works at all. When testing watching the spark , there seems to be too many sparks per revolution, or it might be me misremembering . Does the vision magnet have a nth/sth along it's length?

You are right about running it like this too often and possible damage. It should only be used as an emergency. When I get a working tci or build something with a curve I will keep this hei in the tool comp with my spare reg/rec for emergencies.