O/R Mid pipe install help

fromadig91 said:

Looking to be schooled on the fundamentals of midpipe installation on my 04 Cobra

I just ordered my Magna Flow O/R X-pipe and was wondering if i'm going to be throwing check engine lights what do I need to do to avoid this? I own an SCT livewire and was wondering if I can shut the 02 sensors off with it? Is it just a temporary fix like when I clear any other DTC code or is is a permanent one? To be honest I don't even understand why the check engine light would go on Do I need to get MIL's? what are they?

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A little background: Oxygen sensors react to...oxygen. More oxygen in the exhaust stream (a leaner mixture) results in a lower output voltage whereas less oxygen (rich mixture) results in a higher output voltage. This is how your PCM uses the front O2 sensors to adjust the mixture. The rear O2 sensors are there to tell the PCM how well the catalytic converters are doing their job. If the converters are working well, the voltage of the rear sensors will not swing back and forth like the fronts but will rather move very slowly and with less total voltage change because the cats are changing the chemistry of the exhaust stream. If you remove the cats with, say, an O/R pipe, you remove the mechanism to change the exhaust and the rear sensors produce basically the same signal as the fronts. The PCM sees this and flags a catalyst efficiency error.

A MIL is an electrical low-pass filter. It takes those rapidly moving voltages from the rear sensors and smooths them out with a single-pole filter (comprised of a large series resistor (~1-megohm) and a capacitor (~1uF) to signal ground) before passing the signal on to the PCM. The PCM sees a smooth signal and doesn't flag an error.

Some tuners allow you to turn off the error in the PCM. I don't know if the tuner you're talking about specifically allows this or not. I'd be surprised if it didn't. Most dyno-tuners can do this if need be.

fromadig91 said:

Now since the back 02 sensor is producing the same signal as the front 02 sensor due to it being an O/R pipe (No cats to do their job, thus raising a red flag) is that going to cause the car to run rough? Or effect the car at all? Is it just a CEL that comes on?

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The rear sensors aren't used for trimming the fuel delivery, only to monitor the efficiency of the cats. You shouldn't see any ill-running effects as a result.

Life is too short to do exhaust work, I suggest taking it to a muffler shop for install.

Kilgore Trout said:

Life is too short to do exhaust work, I suggest taking it to a muffler shop for install.

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So true, They can stand up under the car and work, instead of being
flat on your back. Probably cost about $100. But is it legal for a shop
to install a catless midpipe........?

In my town the muffler shops are not too concerned about legality. They offered to chop out my cats but told me I would not be getting a receipt for the work...