Hi Matt,
Sorry for my late response. I was out of town these days...
Thank you very much for you detail testing.
* Speed sensor circuit
I agree the circuit-A works best.
But, I guess it got some noise too, which means a single pulse recognized multiple pulses.
I wrote it "noise", but you can refer it switch bouncing or chattering.
Please refer to the attached figure.
You wrote your speed sensor probably sending 2 pulses per revolution. If the number is correct, the distance parameter' should be about 5144, twice as 2572(4 pulses/rev).
I'll try to make another interface circuit including the noise cancelling capability.
* Injector pulse
I think the 0.0 msec number is caused by overflow of the counter value.
Usually, the injector pulse goes to 0V when the injector is ON state.
But, I think your injector pulse is opposite, 0V-OFF/12V-ON.
I'll try to program of the processor to meet the signal above.
Please give me about two weeks and I'll send them to you.
Regards,
Yoshi
landspeed 
landspeed 
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