tach wire, snowmobile

I'm installing a remote start system on a snowmobile. I'm using the fuel injector for the tach signal. The manufacturer wants to know the frequency (hz) it runs at to shutdown in case of over rev. I used my buddies my scope and i came up with the # of 60 hz at idle 1300rpm and 105hz at 3000rpm. Well the manufacturer sent me the unit with these settings and the over rev function does not work. I look at another post and it said the injector fires once for every 2 strokes. With that info, i did some math and I came up with the anwser of at 1300rpm the frequency would be at 10.83 and at 3000 rpm the frequency would be at 25hz.. Does this sound right? Any help on this would really be appreciated. Also this is on a  4-stroke snowmobile. Thanks 

ttt

I believe that it depends on if you have a batch fire or sequential fire system. With batch fire it would typically fire once per crankshaft revolution and with sequential it would fire once per camshaft revolution (only on the intake stroke) so in that case it would be once every other crankshaft revolution. So if I'm thinking correctly on this, the math would be either:

1.)Batch Fire
1 injector pulse per revolution x 1300 rpm = 1300 pulses/minute
1300/60(seconds per minute)= 21.6 hz

Same math at 3000 rpm = 50 hz

2.)Sequential Fire
1 injector pulse per 2 revolution (or .5) x 1300 rpm = 650 pulses/minute
650/60 = 10.83 hz

And at 3000 rpm = 25 hz

Anyway, that seems correct to me but since you have access to a scope, I'd just verify that you are reading it correctly & try it again. It should most definitely give you the correct answer.

Todd

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