My 99 blazer has 140,000 miles. Hearing a rattle under very slight acceleration. I had a friend rev the engine while I crawled under and it sounds like its coming from inside the cat. It's a "tinny" metallic sound like broken baffles. It doesn't seem to affect performance, but i know these pieces can get lodged in the tailpipe.

should I have a muffler shop do a back pressure test?

Also, the temp of the exhaust pipe before the cat is much hotter than the cat itself. don't know it they should be similiar temps, but a big difference in my mind would indicate a possible obstruction?

Last thing. If anyone has replaced their cat (and I want to stay as close to stock if I have to replace it) what brand it the best for these trucks.

thanks!

 

If the catalyst has broken free inside the converter, it typically results in a dull tapping/rattling noise akin to a plastic mallet banging on metal. If you were to take a plastic deadblow hammer & smack the converter, the rattle should be heard after the impact.

To a certain extent, inlet temperatures will be slightly higher than the main case temperatures due to the expansion of the exhaust gases in the case itself. The outlet temperatures should be nearly the same. Excessively high inlet to outlet temperature differentials could be a result of a restriction.

As far as what brand to go with, the magnaflow universal converters seem to work fairly well. If you have problems after the replacement with a catalyst efficiency code, just get a spark plug anti-fouler & drill it out so the post-cat sensor fits and that should take care of it.

 

Thanks for the help! I'm not familiar with the spark plug anti-fouler & drill it out process. Do you have a link for that?

 

From another forum (hope i don't get in trouble) but i got tired of typing this all out.

O2 Sensor modification using spark plug non-foulers

They're using it to lean the mixture on that link. But fear not you will not lean your mixture by doing it to the after cat sensor. After cat sensor is ONLY there to monitor catalyst efficiency. DO NOT do this mod to your pre cat sensors.

Also, there is a place near me that is an EPA certified catalyst repair facility. They made me a new cat with the factory flanges for under $300, if there's a similar place near you that could be a possibility for ya.