My K&N order arrived already and I have ordered the silicone intake reducers with clamps…

But, the tach input thing… The diode thing didn’t work, but I think I have figured out why. Anything that connected the two coils to each other caused the engine to die pretty much immediately. I used multiple diodes, low and high value resistors, capacitors. Didn’t seem to matter. Anything that allowed any electrical signal to cross from one coil to the other failed.

I would need a working ‘scope to verify this and I own one but haven’t seen it in years. Maybe it was lost in a move or maybe it’s buried in the storage building. Anyway, I think all these coupling experiments failed because the ignition unit may output a burst of high frequency pulses for each spark rather than a single DC pulse. It’s probably well beyond the frequency response of the tach input, so MegaSquirt still sees it as a single pulse. I suspect that this burst may also be over 12V, but if so, my meter can’t catch it.

In short, this means that, in order to use MegaSquirt properly with the stock ignition, I will need to use optoisolators and OR their outputs together.

What would probably be better is to go ahead and convert the ignition system, since I plan on doing that anyway. I was hoping on getting the fuel system fairly well tuned before adding another complex issue, but what the hey…

The primary task to accomplish for the conversion is the construction of the trigger wheel. I should be able to do that with a little bit of jigging and my drill press.

I will also need to purchase the appropriate coil pack. High performance units can be had from Summit Racing for $60, stock replacements from AutoZone for $45 or salvage from $10-$30. I’m leaning towards the Accel unit, though salvage is probably fine and would include a connector. I will need the $15 wireset, too, but will probably need to cut them to length and/or change the plug connectors.