13 replies to this topic

[TR6]

I have a 2002 Spec Miata. It has a 2nd o2 sensor downstream that was orphaned when the spec exhaust was installed. It had been just zip tied up to the e-brake cable for a long time but I just removed the e-brake and decided that this o2 sensor and cable needs to go if it serves no purpose. I just cut the wires (there are four of them). Now of course I have the check engine light which I kind of expected. Is there any downside to cutting the wires (other than the CEL)? I can splice it back if there is but I'd rather not have the thing zip tied under the car if I can avoid it. Should I do anything with the four wires like splicing any of them together? Will doing anything with the wires prevent the CEL?

[HoneyBadger - BrianW]

No downside except for the light. I just cut mine off as well. The car does not use that O2 sensor for any of the engine tuning. It is simply for emissions.

[Kyle Burkhardt]

I missed the rule that said you can remove it.

[HoneyBadger - BrianW]

I believe it is covered here:

4. The factory exhaust system beyond the OEM front down pipe may be replaced, provided the following are true:
a. The replacement system retains the original configuration (i.e., single tube design) and the tubing is a maximum of 2.25 inches outside diameter.
b. The pipe may end anywhere after the rear subframe. Forward of the rear subframe, the pipe must follow the original path of the OEM exhaust system.
c. No expansion chambers. A single muffler may be added.
d. The system meets all event specific sound requirements.
e. A catalytic converter may be gutted, removed, or replaced with a catalytic converter replacement pipe. The replace- ment pipe must not exceed 17.5 inches in length and have an outside diameter no greater than 2.375 inches.
f. No portion of the exhaust may be wrapped with any type of insulating tape, nor shall any portion of the exhaust, internal or external, be coated with any thermal coatings.

[Eau Rouge]

And wouldn't "original configuration" include an O2 sensor bung?

[HoneyBadger - BrianW]

Sorry, here is the correct section under Spec Miata specific rules, section m. Exhaust system:

3. The post catalytic converter oxygen sensor may be disabled, replaced, relocated, or removed; the resulting hole (if present) may be plugged. Original exhaust system heat shields may be removed.

[Kyle Burkhardt]

Just testing you guys. You all passed!

[Cy Peake]

I ziptied mine to the top of the subframe brace pointing rearward.

[TR6]

Will the rules allow me to put a piece of black electrical tape over the check engine light?

[davew]

Although removing the secondary O2 sensor is legal, I do not recomend it.

Removing the secondary O2 does not effect performance, but it will turn on the light. Thus making the light irelevent if something in the system does need attention. If the light is on all the time, or taped over, or removed, you will have no warning of a second problem.

The wire harness can easily be feed back into the interior, then bundled and secured with the sensor attached.

I would highly recomend against cutting the wires, follow back to the connector and unplug. One of the wires is a 12volt source for the O2 sensor heating element. Should that wire short and blow a fuse the car may not run.

dave

[FTodaro]

Although removing the secondary O2 sensor is legal, I do not recomend it.

Removing the secondary O2 does not effect performance, but it will turn on the light. Thus making the light irelevent if something in the system does need attention. If the light is on all the time, or taped over, or removed, you will have no warning of a second problem.

The wire harness can easily be feed back into the interior, then bundled and secured with the sensor attached.

I would highly recomend against cutting the wires, follow back to the connector and unplug. One of the wires is a 12volt source for the O2 sensor heating element. Should that wire short and blow a fuse the car may not run.

dave

on my brothers Miata the 02 wire some how got into the exhaust pipe and melted, when it did it shorted out, blew a fuse that shut down the computer car was dead.

[TR6]

Although removing the secondary O2 sensor is legal, I do not recomend it.

Removing the secondary O2 does not effect performance, but it will turn on the light. Thus making the light irelevent if something in the system does need attention. If the light is on all the time, or taped over, or removed, you will have no warning of a second problem.

The wire harness can easily be feed back into the interior, then bundled and secured with the sensor attached.

I would highly recomend against cutting the wires, follow back to the connector and unplug. One of the wires is a 12volt source for the O2 sensor heating element. Should that wire short and blow a fuse the car may not run.

dave

Hi Dave. If you feed the o2 sensor back into the interior, will that cause a problem with the heating element in the sensor inside the car? Unfortunately, I've already cut the wires but I could splice them back to the sensor cable.

[davew]

Hi Dave. If you feed the o2 sensor back into the interior, will that cause a problem with the heating element in the sensor inside the car? Unfortunately, I've already cut the wires but I could splice them back to the sensor cable.

I would not put the sensor under the seat cushion, but zip tied to the cage will be fine.

O2 sensors need to be worm to operate properly, so OBD1 cars had a timer built into the ECU that disregarded the O2 reading for a set period of time. When they went to heated o2's the ecu was able to use the o2 reading much quicker. And the sensor became more reliable, because they did not carbon up as bad when the engine was cold.

Dave

[TR6]

Thanks, Dave. When I get some time, I'll probably wire it back together and do as you suggest to keep the CEL off.

Hey, you could be on to something here for cold weather racing... a seat heater made from the o2 sensor!