View Single Post
Old 11-30-2015, 01:54 AM   #303 (permalink)
Master EcoModder
Ecky's Avatar
Join Date: Dec 2011
Location: New Zealand
Posts: 5,008

ND Miata - '15 Mazda MX-5 Special Package
90 day: 40.51 mpg (US)
Thanks: 2,866
Thanked 2,505 Times in 1,549 Posts
Originally Posted by Ecky View Post

You might notice a very conspicuous CEL on my dash. Funny story, that.

Before I left Florida, I loaned Gaptooth to my father-in-law. He put nearly 500 miles on it, and when he brought it back, he said the car had been "running a little rough". A quick glance at the FCD revealed he had averaged about 33mpg, and it was vibrating like a jackhammer. Apparently one of the spark plug wires had come loose shortly after he left, and he had been running on two cylinders and dumping 1/3 of the fuel out through the exhaust pipe. The code read something along the lines of, "Catalytic converter performing below threshold". I was hoping driving it would clean up the cat, and at first thought it worked (went nearly a thousand miles before the light came on again), but the CEL has been coming on more and more frequently. It doesn't affect MPG or performance and I can slip past inspection by clearing codes before going in, but the yellow light bothers me so I'm probably going to get a replacement soon.
This weekend I decided to tackle the catalytic converter not working, as well as rust-proof a few more parts. I've seen enough pictures of exhaust bolts turned into fuzzy nubs to want to proactively protect things.

Here it is:

Some of the bolts were pretty stiff, and required that I use a breaker bar to get them free, despite only being torqued to ~16ft-lbs from the factory.

Belly pan let down to access the spring-bolts holding the downpipe to the first cat:

Here it is, with the heat shield wiped down:

I'm not sure what I was expecting, but the mesh inside the catalyst still looked to be in pretty good shape. No visible damage, no melting/fusing, no carbon buildup. Blowing through it had some resistance though.

The solution: Dunk it in a bucket of hot water with some dishwasher detergent and dish soap.

Meanwhile, bolts are soaking in phosphoric acid to remove the rust:

8 hours later:

I rinsed the cat out, ran a pint of acetone through it, shook it around, and let it dry for a while. Mesh didn't look really different afterward, but then, it didn't bad to begin with.

Everything treated with phosphoric acid, then painted with high temperature Rustoleum paint, and anti-seize on all of the bolts:



Drove it around spiritedly, CEL came on as soon as the Catalyst test finished. Let it sit overnight, reset codes, drove it around, and PASS!

I guess I'll see if it stays off, but at the very least, I've restored it to the point that it doesn't come back on immediately.

And for anyone interested in what this car sounds like without exhaust plumbing attached:

Last edited by Ecky; 11-30-2015 at 08:57 AM..
  Reply With Quote
The Following User Says Thank You to Ecky For This Useful Post:
California98Civic (09-05-2016)