ZGA. California/Federal Emissions Conversion

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Evolution Orange

2000 Miata LS


Emissions Conversion

While I had the dash out, I decided to see what could be done to the wiring to allow me to use a Federal Emissions exhaust system instead of the California Emissions system that was on the car. I wanted to install a 2001 exhaust manifold and the California Emissions system would not work with it.

So, I began researching to see what could be done. I consulted the wiring diagram and tried to locate where the wires were physically located. I also compared another Miata I own to the new one.

I determined there were two major issues. The rear O2 sensor was in the engine bay now, but needed to be relocated to the mid-pipe under the car beside the driver's seat. I also noticed the mid-pipe had no bung hole for an O2 sensor but did already have the catalytic converter in the mid-pipe.

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I then began to trace wires. The two wires, one Red and one Red/Yel with the two pins inserted were traced to California Emissions rear O2 sensor in the engine bay. I tried to locate the route they took, but could not find the exact route.

Notice the two connectors are marked for later identification in the engine bay.

While I was looking, I took the wiring harness apart here, but never found the two red wires from the ECU to the engine bay.

I found the wiring for the Federal Emissions rear O2 sensor was already in the car under the driver's seat. Now I had to find out where the wires terminated under the dash. They did not have continuity to the two red wires at the ECU.

I found that the Red and the Red/Yel wires from the Federal Emissions rear O2 sensor connector terminated on this large blue connector under the dash. There were no matching wires leaving the connector going to the ECU.

So, I cut the Red and Red/Yel wires at the ECU and at the blue connector and spliced them with a length of Red and Yellow wire so the ECU was now attached to the Federal Emissions rear O2 sensor connector.

At the ECU, I attached plug in connectors to the old wires leading to the engine bay so they could be reattached should I want to do that in the future.

The Blk/Wht and Blk/Red wires from the Federal Emissions rear O2 sensor connector ran to this splice block and traced all the way back to the ECU. So they were good to go.

Now the Federal Emissions rear O2 sensor connector was ready for use.

The original mid-pipe already had a CAT as mentioned above, so all it needed was an O2 bung installed. So, I found an old mid-pipe and used it as a pattern to locate where to install an O2 bung on the original mid-pipe.

I heated the pipe and made a flat spot on it for the bung. Then I drilled a hole and welded the O2 bung I got from Summit Racing into the hole. The bolt was used to protect the threads while I welded.

I am hopeful this modification will work as planned, but will have to wait until the car is finished to find out.

The car now has a couple thousand miles since the emissions conversion with no issues. Everything is working as expected as of 3/14/2014.