One of the perks of working for an EFI company is that sometimes you can get prototype parts to install on your car. I'm in the process of putting a 36-1 crank trigger wheel on my '66 Dart, and writing a how-to about it. Here's a picture of the wheel in place.



I still need to make a bracket for its sensor, which will be a common GM sensor that I picked up at the parts store. I'm planning on running accuracy tests comparing the crank trigger to a distributor trigger, although the timing chain probably has 200,000 miles on it, so that might be a worst-case scenario here.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Now that's cool!

Can variants of this part be made? I need a wheel with much lower tooth count to put on the front of my truck's 318 to replace the 4-blade Hall Effect sensor in the distributor...

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Matt, maybe you can get some bracket ideas from my setup here

This looks like it will be a cleaner install then mine. Looking forward to seeing the end result

Dan - I know MSD makes trigger kits for small blocks, and big blocks for that matter. Pricy - summit lists it for 300. Not sure about wether it was meant to drive an msd box or direct stock replacement for distributor.

What I'm trying to do is pretty nonstandard...

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Sorry, didn't know what your intentions were exactly from your previous post.

Well, it's kind of complicated, but the idea is to try to rework some of the most poorly thought out aspects of my '89 D100's halfaѕѕed factory engine management system. The 4-blade Hall Effect switch in the dist is used to provide the ECM with engine speed information, which in turn is used to fire the ignition coil and the TBI fuel injectors. The distributor contains no advance mechanisms; all spark advance is (sloppily) provided by the ECM. I want to change to an advancing distributor but keep the TBI, which would mean maintaining that square-wave signal the ECM's expecting to see from the distributor. I could put a wheel with two (big) teeth on the front of the crank and a Hall sensor above it, that'd work. Or, I could put a magic box from Dakota Digital across the pickup coil wires from a conventional Mopar electronic distributor on their way to the (external) ignition module. The magic box is an adjustable tach drive unit that can be made to look at four reluctor pulses per engine revolution and turn it into two square waves per engine revolution. The ECM's wires formerly looking at the distributor's Hall Effect pickup would now be looking at the output from the magic box. The only remaining slight hurdle would be that the ECM is looking for a square wave that oscillates between 0v and 8v, since that's the voltage supplied to the Hall Effect pickup. The magic box has a 12v input so its output will fluctuate between 0v and 12v. Probably fry something in the ECM. I guess I could put a simple resistor in series with the magic box output, but my RLC circuit knowledge is shaky, and I suspect a resistor would not only round-off the square wave but also be a probable failure point.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan,

I wouldn't try to use a simple dropping resistor, but a voltage divider. If Dakota Digital publishes how much current their box will sink you can size the total resistance appropriately. The voltage divider will simply be two resistors in series with one side connected to the Dakota Digital box and the other to ground. One resistor could be as an example 2.4k and the other 1.2k ohms. This will divide the voltage so that you drop 4V across the 1.2K resistor and 8V across the 2.4k. Take your 8V signal between the two resistors.

Josh

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Joshua

Think you may need a voltage divider as well. Single resistor would act more of a current limit.

Is this the same poor tbi system used in dakotas that failed often? If you don't want to fuss with the fuel system, how about you leave the distributor alone to feed the computer but use a wheel like what you see in Matt's picture to drive the plugs with a ford EDIS setup? EDIS can be had relatively cheap once you figure out the wheel mounting, using junkyard parts and this.

Dan - Interesting idea. The main issue I can see with Hall effect systems is that they often trigger off both the leading and trailing edge of the vanes, so you need the vanes to be a particular length. It would have to be custom made - even with laser cut things like this one, there's economics of scale involved. Right now we'll see how these new trigger wheels sell, but it's possible we may have ones with other numbers of teeth if there's enough demand to justify a production run.

Pierre - looks like a nice bracket setup you have there. I still haven't made any final decisions about what brackets we'll use; I'll probably make some sort of simple no-weld one first, then try to weld up a more elegant design so we can show customers both options.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Cool Matt! Looking forward to the rest of the install.

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Chris'
Autobody
Restoration
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Yup...this system does indeed trigger off the low-high and the high-low transitions. I am not sure if this harpoons my "magic box" idea or not. I really don't think that it would, because all the signal would be used for would be injector firing, and since the injectors are in the throttle body and not at the intake ports, the ECM is only reading engine speed off those transitions, not actual timing. I think if I ever find time to do this project, I will probably proceed along the magic-box route unless someone can figure out why it won't work.

Hope I haven't shanghai'd your thread!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Interesting. And this won't affect the "squareness" of the square wave? I'll try to get current capacity info from the DD people. What would constitute a good vs. bad answer?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Yup. '88-'91 Dakotas, B-vans, and D-trucks with 3.9, 5.2, 5.9 engines.
That is an interesting and tempting option, but seems to me it would require a great deal of fiddling with...what, a laptop computer or something? to dial in the advance curves. I do realise, of course, that doing it my way would also require some fiddling to get the mechanical and vacuum advance curves dialled in, and there is the daunting prospect of creating a vacuum spark advance port in the throttle body...

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Looks like Chrysler was trying to use a 4 cylinder distributor on a V8. Well, they could have done worse if they put their minds to it - at least they didn't go to Mitsubishi and buy the electronics and trigger wheel from an existing four banger distributor, put it on a V8, stick it behind the water pump where mechanics have a horrible time reaching it, and then have their production team decide that the design engineers goofed up on the size of the water drain hole and so size it so small that water can easily drain into the distributor but can't escape, drowning the electronics as soon as the water pump starts leaking.

(That description is, of course, exactly what GM did on the Optispark ignition. Seriously.)

My biggest concern about getting the edges of the signal to line up is that if they're off, the ECU may interpret the signal as rapid changes in the RPM. If the vanes are exactly as long as the gaps, a tach adapter that gives you a 50% duty cycle is likely to work.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

As soon as I got this far, my mind came up with "Optispark!".
Yup. GM also mounted the Northstar starter under the intake manifold and claimed with a straight face "Starters don't fail", and mounted seatbelts on doors, of all stupid places, and claimed with a straight face "Car doors don't come open in crashes".
Ah...now that is something I hadn't considered, that the ECM might be looking not only for the frequency of low/high and high/low transitions, but also for the timing of those transitions relative to each other. I will have to take a look at the sensor and see. Here's what the FSM shows, which makes it look like the vanes are much narrower than the gaps. So the question becomes whether or not the ECM is in fact looking at the relative timing of transitions, or just their plain, simple frequency.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.