my 1982 240D has the EGR system which includes a crank sensor....

At the sensor, you get anything from a 0.1Vpp to 0.4Vpp signal proportional to engine rpm. (unplugged from the EGR computer)

If you go to pin 4 on the EGR computer (with the sensor plugged in), you get 0.5Vpp to 2.0Vpp riding on 2.3vdc.

Sounds like a capacitive pickup ? The computer gives it some DC bias that makes the signal larger (and easier to see ?) I know some electric theory but Cap./Ind. pickups escape me...

I'm guessing the OM617's have an inductive pickup, as they have two signal wires going to the crank sensor. If this is the case, then all I need to do is ground one OM617 sensor wire, and hook the other up to my cap. crank sender so the tach amp gets a voltage pulse.
I still need am OM617 sender signal to compare it to. I dont think that 0.5v will blow the tach amp, but I'd like to know if I'm in the ballpark.

-John

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