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Okay, the zener setup works fine on the VSS, but I think the MPGuino may be double-counting pulses. I got 81700 pulses per 20 miles, or 4085 pulses per mile... about half what the wiki says I should be seeing. I've got slightly larger than stock wheels on my car, so that probably covers the remaining 30/15 pulses per mile. I point the finger at the MPGuino code since it seems far easier for it to be counting both rising and falling edges than my interrupt to be triggering on exactly every other pulse.
My injector microsecond numbers seem within reason as far as the wiki goes... Around 30 MPG for the test trip. Engine warm up, it was raining, most of the trip was up and down I-95 at a fair clip, and I experimented briefly to see what the maximum injector pulse width is (about 12 ms). My back-of-the-envelope calculations say i should be using something like 230 s/gal (rather than 200), but calibration will have to wait until I figure out persistent injector and VSS counters.
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