1997 Mazda MX-5 Miata: Ping
May 29, 2011
Lately, if you give Project Miata a proper dose of throttle after it has had a good long heatsoak in, say, LA traffic, it'll ping. Not just one sporadic event, but several pings scattered through the midrange and up into the red.
When you hear detonation in a car like this, you should back off the throttle, stat. This is how I'm wired, but in this particular instance I had to grit my teeth and stay in it for the duration of the gear.
I did what I could to remedy the ping once I returned home.
I used this:
And got busy on this:
That's the Miata's cam angle sensor. Rotating it adjusts the base ignition timing. It's an easy solution to the detonation situation we have, and it's all we can really do.
The Miata's old school. It has no knock sensor. And the Kraftwerks kit relies on its modest nature to get by without the additional expense and complexity of adding knock control. So when you hear pings, all you can do is adjust the cam angle sensor to retard the timing.
When you adjust the cam angle sensor, you globally scale the ignition map -- the whole thing is advanced or retarded. This sucks because you really only want to retard the timing for one condition of full load and at certain revs, namely, where the ping occurred.
By retarding it everywhere you give up performance (and fuel economy) everywhere in the engine's operating range. The additional retard also needlessly increases exhaust gas temperatures, too.
I nudged the sensor back a couple degrees. We'll see if it kills the ping.
I'd love to experiment with a proper knock correction system on this car.
Jason Kavanagh, Engineering Editor