Busted "J Pipe"?

BondoBob

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2001 Mazda MP3 - Blue
Well, this week sucked.

Last week, I dropped off my MP3 at my mechanic for state inspection, a couple more tires and to fix the problems I've had for a while with two engine codes (PO421 & PO300). A coil pack and two O2 sensors later, things are looking good and while visiting the shop to check on the progress, they were trying to clear the last two codes from the computer so I could get my inspection finished. Mike suggested I drive it out to the Jones Beach water tower and then take it up Merrick Road, stopping once and shutting it off before heading back to the shop (about 25 miles). I noticed the exhaust was just a little throaty while driving out toward Lido Beach but the engine was revving freely and feeling better than it had in a while. As I was running it through Jones Beach State Park, the exhaust began to get louder and by the time I returned to my town, it was race car loud.

Putting it up on the lift, we noticed that the pipe coming off the cat right off the engine (and the lower O2 sensor threads into) was rotted...actually just the back end of it with the donut and the springs holding it together on the flanges that allows the engine to rev without pulling the pipes apart.

Now, I am waiting for a new pipe and the springs/gaskets/whatever (the rest of the exhaust is in great shape even with the 80K on the car).

Why the hell does this one piece (a cast piece - not tubing) go like this? Is it normal?
 
I could go with a header, but since I've been chasing problems with CELs, I don't want to introduce new problems (eliminating the first cat) and the pipe and all the fixings are already on order.

The J-pipe is fine except for the downstream end where the spring-loaded bolts should attach which makes it worthless. I'll try to grab a picture before it hits the trash.

I'm curious why this thread was moved to the MP3 section as it discusses a part common to all the 2.0 litre Protege engines.
 
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