99 Miata crankshaft sensor on Microsquirt V3

[JeremyS]

I am in the process of installing a Microsquirt V3 w/3.4.2 into a car with a ’99 miata motor. I’m hoping that someone can provide a definitive answer on wiring up the stock 99-05 miata crankshaft position sensor. There seems to be a great deal of obsolete and/or confusing information on the web about how to go about this. The ‘Miata 99-05’ section in the latest version of the Microsquirt Hardware manual says to refer to section 5.2.2, which is the VR sensor section and doesn’t seem to apply. The crank sensor has power, ground, and signal wires, and all of the information that I’ve found states that the 99-05 miata crank sensor is in fact some variant of open collector.

I don’t know if it matters, but I’m using the Flyin Miata 36-2 wheel, and I’m not running a camshaft sensor of any kind.

-Jeremy

[prof315]

The CKP is open collector hall effect. Because you are using the 36-2 wheel I would wire the the signal wire to VR+ with a pull up. Use toothed wheel not Miata 99-05 and not Miata 36-2

[JeremyS]

Thanks for the info. Out of curiosity, what's the reason for VR+ as opposed to VR-?

[slow_hemi6]

Your sensor with a pull up resistor only operates in the 0 to +V range, if you have no negative (sub 0) voltages then using VR- doesn't make sense. A VR sensor on the other hand outputs a sine like wave with positive and negative excursions.

[jsmcortina]

For historical reasons the external connection called "VR-" is connected to the IN+ pin of the MAX9926 chip.

James

[JeremyS]

For historical reasons the external connection called "VR-" is connected to the IN+ pin of the MAX9926 chip.

That helps to clear up my confusion. The Microsquirt hardware manual shows the hall effect sensor with pull up connected to VR-, which seemed counter-intuitive until your explanation.
It looks like I just need to connect the signal wire to the input labeled VR1- with a 5v 1k pull up.

Thanks all