denso electronic ignition

[ecurbruce]

Inspired by the posts related to GM HEI ignition, I set out to develope and create an electronic ignition system for my 250 monza. I had not the first bit of electrical equipment with this project, so it's no loss to use something other than origional equipment as an end point. And I just enjoy creating stuf.

After several trips to the salvage yard, looking at just what is useable and what's not, I chose the Nippon Denso unit used in an early 90's Dodge Dakota 4 cyl. distributor, with a single 12 volt coil, and ballast resistor.
It has the postage stamp sized module and pickup coil neatly tucked into the bottom of the distributor, both pieces miniature in size, and will be well suited for my project. The Dakota distributor also uses mechanical advance, which means I can retain the mechanical advance on the Ducati engine.

The system works well, pickup coil mounted on a plate to replace the points, module mounted on top tube under tank, behind coil, and I welded a half moon key to the points cam, then filed it down to a .010 in. air gap. The pickup coil is adjustable on the plate, so the air  gap can be dialed in.

The process was not without challenges, I started with the pickup coil wired up backwards, which resulted in no activity at all..., tried using a Ford single plug coil from a late model Focus four cylinder engine, it ultimately may have worked after all the other bugs were worked out, but it was difficult to mount to the frame...

The biggest stumbling block,(and what almost made me scrap the whole system),in the first version I inverted the pickup coil on the mount plate to make the unit fit in the points cavity better. I got spark, but the engine wouldn't run. I was almost convinced my (mikuni 26mm) was no good, when one time after severely flooding the engine, and with the timing a bit too advanced, the engine ran noticeably better BACKWARDS! Actually,it was the first time it ran at all. This prompted a re-design of the pickup coil plate, this time with the coil upright, as it was  in it's original distributor. It works fine set up this way, and runs with a good strong spark!
This tells us that the pickup coil is definitely  sensitive to direction of rotation, and also to polarity of the leads attaching it to the module.

I ended  up using a 12 volt coil from a chevy sprint which uses this same distributor and module setup (denso), as a matched set. I'm running a .040 gap on a BR8HS for now, may change that later? Also worth mentioning, this is a 12 volt battery system, don't know if it would work with the batteryless system?

I haven't found a good way to set the timing yet, I set it static with a degree wheel, but not yet with a timing light or anything else. I haven't figured out a good way to do that yet?

I have about $30.00 invested (and about 6 months) so far!!!

photos are on the way.

[ecurbruce]

185.JPG

This is the first attempt where the pickup coil is upside down on the plate. (will not work this way)

256.JPG

Second attempt, notice pickup coil is inverted, back to origional configuration. It runs well.

257.JPG

photo of coil and module mounted to top tube.

[Jordan]

Nice work, Bruce.
They must be compact parts to fit in the single's CB space. That reluctor - did you grind it up from a standard cam?
It's curious that the pickup is sensitive to rotation direction. Running backwards, it probably makes a mirror image to the normal waveform shape, but I think changing the 2 pickup wires would get it back to normal.

Jordan

[ecurbruce]

Jordan,
Thanks for the reply, yes it's been lots of fun.
You asked about the reluctor, yes that's an origonal points cam, so it's still operating the mechanical advance behind there, but I did have to add some material to the cam then grind the reluctor shape to fit the pickup coil.

Jordan, you mentioned " changing the 2 pickup wires would get it back to normal",
I tried that a couple of different times, it seems the processor in the module is accepting a specific signal from the pickup coil. If the wires are reversed to the module the result is no spark at all.
I noticed one time while checking the resistance of the pickup coil (disconnected from module), as I passed the reluctor by the coil in one direction, the resistance would drop then recover back up, while as I passed the reluctor in the opposite direction, the resistance would rise and then recover back down. This was my first clue that the coil is sensitive to direction. But it will only make spark hooked up one way only to the module.

Bruce

[wcorey]

Nice job on that Bruce, I like the way the pickup bracket is integral with the mounting plate.
I was originally using the same ones when I was playing around with the hei modules, had a couple left over from ~20 years ago when I was then putting them on brit bikes. They must be very a tried and true design to still be in current use after all these years. When I found the Honda xl magnet triggered one, I ended up going with it instead (for whatever reason).
Was getting them then from older Toyota Celica's, the ign module was quite a bit larger though. I'll have to scrounge a couple newer ones next time I'm at the bone yard.
I can't remember why but I had also had to retrofit a different mounting bracket, must not have fit with the original one.



Bill

[ecurbruce]

Wcorey says:
"Was getting them then from older Toyota Celica's, the ign module was quite a bit larger though. I'll have to scrounge a couple newer ones next time I'm at the bone yard."

Hi Bill,
Ifyou look for the small module, it's inside the stand alone distributor, the ones with just two wires exiting the housing and going straight to the coil.
So it seems I've tapped in to an already good idea,

Bruce