1) Last time I entered the tach problem, I had thought that I had it solved. I did on the bench, and the tach worked well and accurately. So I reinstalled it and ran the engine again, but this time got very odd readings, odd multiple of the revs shown on the optical device. so back to the bench. 2) Test setup, but with different arraingment of the magfnet. I broke the single magnet into two different ones, and made sure the same poles were crossing the sensor, N--S wise, and mounted the two pieces to the support as shown. the scope indicated nothing wrong and the tach coulted exactly twice...two magnets. I removed one of them, and the tach counter very close to the scope readings. Humm. Not a random counting that I had in the A/C.
