What sensor is this on back of 2004 VVT head?
 

Sensor above coolant sensor?

https://www.miataturbo.net/attachmen...ine=1409915983

Have not seen mention of this before.

It's not a sensor, it's a condenser, aka a big capacitor.

is it for the ignition system?

Never seen that or that bracket before.

Thanks Reverant, I saw mention of it as a condenser in another thread, however it looked as if it was located in a slightly different spot. My guess is that with using my COPS, I can delete that.

Yes, it goes between the + and GND wires supplying the ignition coil primaries.

To the best of my knowledge, all Miatas have one. On the 1.6 cars, it's tucked up under the fender lip near the igniter module. Not sure where it is on the '94-'00 engines.




It's not a bad thing to have in place- its primary function is to smooth out the supply ripples caused by the coil primaries switching on and off. Commonly, a very large capacitor or capacitor bank (on the order of 10,000 uf or more) is installed as part of a COP conversion, but even so, there's no harm leaving the stock unit in place.

Its certainly not in the coil harness for the 94 coils. And I'm not using it for the 01+ coils on my car now. I wonder if the lack of this capacitor could be causing some of my crank trigger noise.

Leafy, on my COP conversion, I put 4 of these (Nippon Chemi-Con 10000uf 25v 105C Axial Capacitor) between the + and - going to the COPs. Probably overkill, but did help with some lost sync 39's I was seeing on the MS3.

The other picture that I saw of this looked like it was mounted on top of the valve cover toward the right rear.

Curious if anyone uses these in their VVT NA swaps. I appear to have left mine out & wonder if it should be put back in..

iirc, your car won't start without it.