1997 Mazda MX-5 Miata: Power Restored
May 23, 2013
Holy crap. Project Miata's new catalytic converter has really reawakened this ol' tic-tac. To recap, the car had been feeling gradually less peppy, and finally the check engine light illuminated. At that point the car was also more detonation-sensitive than before and drivability had degraded a bit, too. But none of these aspects were overly prominent, just a collection of incremental nuances that I apathetically chalked up to age and hard use.
I discovered that its catalytic converter had gone bad and replaced it. Upon startup I immediately noticed the deeper exhaust note. This is an indication of reduced backpressure. Basically, the old cat had become a huge exhaust restriction, a banana in the tailpipe. The backpressure was choking off the engine. In the words of an old racer friend, the engine "couldn't eat 'cuz it couldn't poop."
Replacing the cat made far more difference than I expected it would. All of its earlier bad behavior is now gone. It drives with the verve it had when we first installed the supercharger, and its propensity to ping is now no different than then, too. The power's been restored. No joke, according to my finely honed posterior dynamometer, Project Miata had lost about 50 hp with the old and crumbling cat.
Jason Kavanagh, Engineering Editor