Catalytic Converter

[Pat]

I'm posting this now so as to inform the membership in this thread, Catalytic Convertor, of how to recognize when a CAT is going/gone bad.

Sometimes they rattle on start up or acceleration. May not affect performance since exhaust is flowing.

Sometimes they partially clog up and may throw a CEL Code. This may show up as a "fall on your face" or a bog down decrease in performace when accelerating mild to WOT. Rev's may not climb much over 3.5K.
Low load driving around town may not be affected.

If you have a performance tune, the Rear O2 Sensor signal, behind the rear CATs, may be turned off so no CEL will be displayed.
I am not understanding why tuners turn off the CATs. Someone may know the answer.

Sometimes CATs get so clogged up that the motor will not run.

CAT failure does not occur all at once so do a WOT from time to time and note if performance seems degraded, May need a CAT scan.

A competent exhaust shop should be able to test your exhaust for defective CATs for a nominal fee.

CATs are usually warranted for 8 years or 80,000 miles by federal law. Some exceptions such as mechanical damage of running over rocks or other things that go bump in the night may apply.

Replacing Cats can be expensive. Be aware of price vs products.

Our MM's are aging and for many the 80K mile marker is at hand.

Please add to this thread as necessary. The idea is to use key Words "Catalytic Converter" and find info instead of weeding through a zillion posts.

Regards,

Pat

[ImpalaSlayer]

tuners turn off the rear o2 sensors that are behind the cats, not the cat (not possible to turn off a cat). my guess is with the added timing and fuel fuel flow and what not it could trip the CEL making the computer think that the cats arnt working.

[Pat]

Thanks, Impalaslayer, I edited my post.

[MM_BKK]

Sometime when cats go bad, they can completely hollow themselves out. The car would get noticeably louder and the exhaust would have a stronger smell.
I've had this happenned to Magnaflow cats with ceramic core twice already within a 6 months span. :(
Not sure if the high boost had caused it, but I think I will try metallic core ones next.

[MrBluGruv]

I'm pretty sure one of the two previous owners of my Marauder used cheap gas every fillup, when I still had two of my four on they would afterfire like mad riding down in a gear and would pretty much explode on the inside if the engine ever hit the rev limiter, like one continuous backfire as the revs came down.

Consequently though, removing those remaining two and getting the engine re-flashed to a Lidio tune eliminated any afterfiring issues I had.

Personally, not a big fan of catalytic converters in the first place.

[Pat]

The Testing of CATs can be done by an muffler shop equiped with the right tools.

A small hole is drilled in the exhaust pipe ahead of the first CAT and a probe inserted which is connected to a device that measures air flow/pressure.

This will tell the technician if the CAT(s) are plugged up.

I had mine done today at no charge because of the warranty. My CATs were good.

[Marauderjack]

Cats seldom wear out but the media can break up causing exhaust blockage!!:shake: Most are ceramic and actually pretty tough!!:cool:

If one plugs up without breaking up a VERY RICH condition exists or you are burning a BUNCH of oil or running leaded fuel!!!:eek:

Cats on taxi cabs routinely go 500K miles without problems provided the cabs are tuned, serviced properly AND run unleaded fuel!!:beer:

[jdenning002]

Would having no CATS be an performance issue? Would a new tune be necessary??

[jdenning002]

I'm pretty sure one of the two previous owners of my Marauder used cheap gas every fillup, when I still had two of my four on they would afterfire like mad riding down in a gear and would pretty much explode on the inside if the engine ever hit the rev limiter, like one continuous backfire as the revs came down.

Consequently though, removing those remaining two and getting the engine re-flashed to a Lidio tune eliminated any afterfiring issues I had.

Personally, not a big fan of catalytic converters in the first place.

So are you running no cats?

If so, how did the car run after you cut them out?

Did you have to get a new tune?

[MrBluGruv]

yep right now it's piping of identical diameter in place of the cats, all four.

The car is running great, actually had the last two cut out the day after I uploaded the Lidio tune, car ran like a champ and had zero after-firing problems from that point on.

The low end push isn't there for the car, but it never really was. Now the high-end pull is insane in this car, once I pass 2500-3000 rpms it just runs. I can't wait to get headers. :)

[jdenning002]

I have kooks long tubes, I just cut out the cats on the kooks x-pipe assembly.

I am having a few issues... trans shifts at wrong points, and the car runs a little rough...

It is also a bit louder... I have stock mufflers and tailpipes.

[MrBluGruv]

I'll tell you right now, transmission shift points should have nothing to do with the exhaust work you did, so I'm curious, did you have the vehicle dyno-tuned for the headers? If so a bad tuning job may be the culprit. That's the most immediate thing that comes to mind...

[jdenning002]

The tune was good, I think it might be a bad COP or bad fuel pump...

The car ran great for 6-7,000 miles.

Thanks for the tip on the exhaust not being the problem, I didn't think so...

[justbob]

I've been noticing the drivers side exhaust has twice the sound and morning cold air smoke than the passenger side. The car is also starting to sound like it has a nice set of cams in it at idle.

I've been having issues for months now of a bad bucking at WOT, and sometimes just a constant sputter holding back power, and at worst dying out at WOT.

I think Zack steered me right with replacing the FRPS, because now (so far) it hasn't died or bucked real bad, it just sounds and feels like it's firing on six cylinders only at WOT.

No codes ever. New plugs. Sounds like a plugged pass. side cat....but Bobby has no cash.:(

[fastblackmerc]

Would having no CATS be an performance issue? Would a new tune be necessary??

With no cats you'd see a performance gain since the exhaust has few restrictions, but you'd never get through a state inspection if they check for cats.

[FordNut]

If you beat on the cats with a hammer to make them clear the crossmember, the insides will break loose and they will rattle...

[Marauderjack]

With no cats you'd see a performance gain since the exhaust has few restrictions, but you'd never get through a state inspection if they check for cats.

ZERO performance gain....just a bit more noise!!!:shake: