Quote:
Originally Posted by pmax
I'll play contrarian.
Whatever damaged the secondary probably had an effect on the forward.
And the mechanic is correct, there's crud from the disintegrated cat in the system. Fixing it correctly which of course is gold plating to us but hey, to some ANR types does matter, means getting all that out of the system which leads to that recommendation.
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That very well could be. More information: I did remove the entire exhaust system aft of the manifold / first cat (it's amazingly easy to do on these cars). When I shook the crumbs and pieces out of the second (aft) cat and its piping, material only came out from the front, which would make sense if it was blocking the system. I did the same with the section of pipe with the resonator (which is aft of the second cat), the aft "Y" pipe, and both mufflers. Can't be too careful... None of these either rattled when shook nor was I able to dump any material out of them. In light of that, I'm relatively confident that all of the degraded, loose material was captured in front of, and came from the front of, that second cat. Which, of course, made me think it all could very well have come from the first, or forward cat.
If the first cat (the forward cat, the one in the manifold) had failed, one would expect the check engine light to come on, with a code generated by the O2 sensors. The fact that that never happened is an indication that the forward cat was fine. A visual inspection - and I could see most of the honeycomb with a mirror and a flashlight - indicated that the forward cat was fine as well.
One aspect of all of this that I find quite troubling is the fact that their "best, most experienced" mechanic is so unfamiliar with this car that he thought the second (aft) cat was actually the first (forward) cat, and that the resonator was the second cat. He could not understand how the cat could fail and not throw a code, since it must have the O2 sensors bracketing it. The fact that this second cat has no O2 sensors in front of or behind it is very, very easy to see with the car on a lift. It's all very exposed and quite visible (that's why I was able to swap it out so fast).
So, he knows it a cat, yet it's quite obvious there are no O2 sensors anywhere near it, and he is puzzled as to why it would not have thrown a code. No O2 sensors anywhere near what he thinks is the aft cat either. You need a flashlight, and you need to know where to look, but the two O2 sensors bracketing the front cat are visible (and accessible enough to easily replace). All you have to do is look...
This guy didn't know any of this, after "50 years" of working on Subarus. And he apparently was not curious enough to perform even the most cursory research - a quick look at a shop manual would have shown him the entire exhaust layout (as it did for me in a quick internet search). Just basic inquisitiveness - "why wouldn't it throw a code?", or "why am I not seeing any O2 sensors?", or "why would the 'second cat' be so darn big and a completely different shape?" and on and on. All pretty darn simple stuff. All stuff I was able to discern in about ten minutes of internet research. I don't even own a shop manual, I have never been trained on Subarus - and it took me ten minutes to figure this out. That bothers me - their "very best, most experienced" mechanic, with "50 years" on Subarus, had no idea what was going on...