Strange that the two mechanics would have such different diagnoses

My mechanic tells me that the driver's side catalytic converter on my 01 Boxster is toast. They did a smoke test on it and diagnosed cracks in the cat housing.
This causes the check engine light to come on all the time.
I don't want to spend $1750+ on a new CC. There's got to be a better way, and I'm hoping that somebody here can help me with some advice.
Are there good aftermarket CCs?
How about a used one?

Sent you a PM.

that what the shop told me replace the both cats and i already replaced 2 back sensors he said the other sensor were fine and diagnosis said none sufficiate cats but the car runs fine horse power and only when i start it up a little smoke then go away white smoke so if you have any advice to share i would appreciate it and what brand for cats? thanks rich. and my boxster has 161000 miles on it .



Edited 1 time(s). Last edit at 10/06/2011 10:17AM by richie. (view changes)

Why not just weld the cracks?

The engine light has been coming on for well over a year, and my mechanic said that the cracks having been there for that long probably caused internal damage; oxygen going in and corroding the internal membranes of the cat. Seemed sensible to me. No?

Cats are impervious to oxygen.

What are the codes?

I don't know the actual codes. All I know is that the CE light kept coming on, and that the first mechanic replaced the rear oxygen sensors, then wanted to replace the front ones. Something told me that didn't make any sense, so I went to a different mechanic who blew smoke into the exhaust system from the tailpipe, and found the cracks. They are telling me I should replace the cat, or I could weld it, but that would cost the same labor, and may not fix the problem...
I've found somebody who has a pair of used cats (40k) they are willing to sell them to me for $400 (although I only need one).

What's your advice?

The cheapest thing to do should be to weld it. The $400 cats are likely fine but welding shouldn't cost anywhere near that unless the cracks are extensive. If they are, I would definitely replace the cat.

It's a little strange that neither of the mechanics inspected the cats while the car is running. Exhaust leaks are usually pretty evident as they produce a low pitched percussive sound, wind, smell, and dripping water (when the car is cold).

Oh, the second/current mechanic did inspect it while the car was running. He said he heard a sound. Then he turned the car off, put the smoke thing on the tailpipe and blew smoke into the exhaust system. Then he found the cracks by looking at where the smoke came out. When they weld it, do they do that while the cat is on the car? (I can't imagine that).
Otherwise, there'd definitely be the labor cost of taking the cats out, right?
Somebody else offered me his cats left over from a racing conversion for way less. I might go with those instead but have to still follow up to see if they are the right parts. The place the mechanic showed me that had the crack and where the smoke came out was a piece with three metal pipes coming out of a metal chamber. The cracks were on the two exterior pipes. Not sure if that piece is actually the cat...
Thanks for all your insight on this...

On your car, the headers have a pre-cat built into them. There is a separate secondary cat. I can see how this could get confusing.

IMO, it is much more likely that the cracks would be on the headers/pre-cats. Parts cost-wise headers are generally much cheaper than cats. It sounds from your description like the problem is on the header. Labor to replace the header (or remove it for welding) theoretically should be under an hour but in reality since the bolts rust and seize in the engine, it can take up to several hours.

If you're comparing the cost of replacing the headers versus welding them, I can easily see the costs being comparable. And in that case, I would replace them.

Make sure the car is in a complete vacuum when they are installed. Mechanics hate that job, holding breath for an hour and stuff. Yuk.

Of course you can fix it if the structure is sound enough to take a weld. of course, it may not be.

Let your mechanic turn wrenches and refrain from Chemistry commentary :-)

Grant

I am still a little bit lost on this. Maybe a little mre than when I started out.
The piece that has the crack, and that needs to be replaced or fixed looks like the one here

The cracks are in the two outer pipes of the manifold.

The challenge I have is that the part that the kind people here have offered me look more like this

Naturally the two look nothing alike.
My mechanic tells me that on this year, the manifold is part fo the catalytic converter. THe first picture above comes from an ebay listing for an after market cat:
[cgi.ebay.com]

Does anybody here have any experience with these? I've heard all kinds of bad stories about aftermarket cats not fitting right, or working right, etc.

Again, thanks for sharing your wisdom!

The first set (primary cat) is built into the headers, which are cracked on your car. The headers are sometimes incorrectly referred to as the exhaust manifold.

You need a replacement exhaust header, like the one in the eBay link you provided.

The second pic you provided are of secondary cats, which are expensive and do not need to be replaced on your car.

Ah!
I get it now.
Well, if somebody here has a primary cat/header they want to get rid of, I need one.

More advice needed:
I went back to my original mechanic. I've been going to these guys for 5 years, and they are very knowledgable, but I do want to ask you guys, especially Boxsterra.

They did the smoke test the other guys did, and there were no leaks/cracks in the catalytic converter. No smoke came out anywhere. There were some very light deposit around the top of the manifold/primary cat header pipes that could be from a leak, but they were very, very minor.
So my mechanic is saying, either replace just the post cat O2 Sensor (I had the pre O2 sensors replaced about 8 months ago), and see if that does it. Don't worry about replacing the cats just yet. They knocked against the cat with a rubber hammer, and couldn't hear anything lose in them.
So now I wonder if I should do that, or if I should replace the cats.
They'd charge me about $200 to replace the oxygen sensor ($120 for the part + half and hour labor).
Should I do that?

What if the cat is bad? As I understand it, the new O2 sensor would take a while for the tip to collect enough residue to turn the CE light again. Is that correct? (if it were, wouldn't that mean I can just unscrew the O2 sensor and clean the tip?) Or would a bad cat cause the CE light to come on again immediately even with a new O2 sensor?
BTW, the fault code is P0430 on bank 2, something about efficiency.

Also, does the engine run differently when the CE light is on? Does the computer change anything about the fuel mixture, or anything else?

Any advice would be greatly appreciated.

Are you sure they're looking on the correct side? It should be the left side of the car (driver's side in the US).

It is unlikely that the cat is bad. But if it is, there is a separate 10-year warranty on that part and the dealer might replace it for free.

I wouldn't just replace the O2 sensor. I would swap the front and rear sensors (they are the same part) and see if the problem goes away.

Thanks guys. I had my mechanic swap the post cat O2 sensors. If the fault moves with the sensor, we know the O2 sensor is bad. If it doesn't I'll buy used pre-cats/headers. I drove around a little, but thus far the CE light hasnt' come on yet. And I'm going on vacation for 3 weeks, so the car will be sitting for a while. We'll see when I get back...
Thanks for all your help thus far. This place is a great resource. I would have never thought of swapping the sensors if I hadn't read it here. And my mechanic didn't think of it either. That's a little bothersome. But then they are in the business of replacing things and making money that way. Diagnosis doesn't make their cash register ring...