Exhaust Issues

[Crazy_pilot]

Well, the fun begins.

I brought my car to get safetied. The mechanic came back saying I need new pre-cats and new O2 sensors. The left pre-cat has a small hole on the pipe and a larger on in the flange weld. The right one is so badly rusted it will probably be broken trying to get the left one off.

Pre-cats are about 650 each, O2 sensors run about 180 each.

I've already figured it'll be cheaper to buy new Magnaflow pre-cats (PN 50004) and a new Magnaflow main cat (PN 94007) and weld in some piping. Each cat runs about $100-$130.

My question is, are the O2 sensors simply supposed to be replaced when changing out the pre-cats, or is the ECU throwing a code for them? The check engine light is off.

Thanks!

[svxcess]

You can get by without the pre-cats and just tubing into the 94007 Magnaflow high-flow cat and back to the rest of your exhaust system.

I replaced my pre-cats with stainless steel Aero resonators ($82.00 each) and into the 94007 cat without any problems. Mine is a 1996 OBDII.

If the O2 sensors aren't throwing a code, leave them alone. When I redid my entire exhaust system, I used the original O2 sensors and all is well. No CE light.

For a look at my exhaust without pre-cats, look in my locker HERE

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[Crazy_pilot]

Wow, that's a nice looking system.

Does not running the pre-cats cause any trouble with emmisions testing?

How does it sound with the resonators in there?

[svxfiles]

Originally Posted by Crazy_pilot

Wow, that's a nice looking system.

Thanks!

[svxcess]

Originally Posted by Crazy_pilot

Wow, that's a nice looking system.

Does not running the pre-cats cause any trouble with emmisions testing?

How does it sound with the resonators in there?

No problems with emissions testing at all. I never got a CE light and the O2 sensors don't seem to care, since they are after the pre-cats. I also have the third O2 sensor in the pipe behind the main catalytic converter (OBD II) In the original configuration, the third O2 sensor was in the rear of the stock converter. We put it back in the pipe for accessibility if needed.

My car went through MD emissions testing 2 weeks after the conversion and passed without problems (I also have 103,000 on the original plugs.) The Magnaflow cats are 49 state legal and all you need is one. The 94037 has the third O2 bung, but I used the 94007 because I didn't need it.

As far as the sound and performance goes, check this thread, starting at post #42. You can also read the entire thread for background.

http://www.subaru-svx.net/forum/show...t=37523&page=3

Simple and effective. As quiet as stock but at a lower frequency.

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[Earthworm]

The question now is how much time do you spend under your car polishing that exhaust?