Anyone ever replace a cat on a V8?
 

Finally got my Check Engine Light code diagnosed, and as I feared it was PO-42 - catalytic converter not working well enough. It's a MBZ SUV with 200K+ miles.

One cat from MBZ is $640 - parts only. A local muffler shop my company does business with thinks they can replace both cats for around $700 - but they will not be oem. They say it will take care of CEL and that both should be replaced.

I can hear what sounds like a rattle or marbles coming from the drivers side cat.

I think in CA now you are supposed to just use the oem part, but if my emissions are fine and the CEL is taken care of, why not go aftermarket?

Never heard this. There is a huge aftermarket for cats, I'd look into that one some more. Just make sure that it's a good replacement part w/ the same or better flow (back pressure) than the original. I've seen a lousy aftermarket cat ruin the performance of an older Benz. :cool:

I have an aftermarket car on my truck and it's passed a couple of times. You won't likely get the mileage out of an aftermarket, but if it's CARB approved, you can install it and go pass. Also, I don't have a Porsche car on my '88 and it passed fine. It came from our host and is a quality unit. You might be able to get cats for your MBZ thru Pelican.

first of all, cats don't belong on v-8's, it ain't there natural habitat
cat's don't like loud noises, or the vibrations and heat involved with such things

second of all, i don't see what the fuss is all about if one does have a cat on a v-8
and wants to replace it with another cat

here's a top tip
cat's don't like water

so to get rid of the old cat.. just put the hose on the little bastard
it WILL run off

then simply put the other cat on top of the V-8
i really don't know how you can make it stay there..
maybe some grilled steak or chicken will work, but i doubt it will stay there forever...
cat's tend to bugger off once the they have finished feeding...

just my 2cts worth

I don't know why cats are even mandated on modern fuel-injected cars, they only catch things when the air-fuel mixture is not correct. This was a problem on carbureted cars, as they could not be continually adjusted. Fuel injected cars make several adjustments a second, and about the only thing the cats do is hurt gas mileage.

The rattle you hear is likely the broken bits of cat gut. These cats, unlike those that Stijn uses, often have a ceramic honeycomb internal structure that is coated with palladium, rhodium, or platnum (which is why they get stolen). As they age, they can crack, breakdown, etc, leaving you with crumbled honeycomb rattling around.
http://en.wikipedia.org/wiki/Catalytic_converter

Any quality aftermarket cat should be fine to replace the OEM.

It's a mixed bag. You used to be able to replace a cat with a generic version and no problem it would pass.

I tried this recently on a Toyota and the CEL is still lit. No facts to back this up, but my bet is the aftermarket version while physically similar isnt the same inside.

If the shop will guarantee the light will go and stay out go for it. Otherwise you could be wasting $$.

OBD-II cars have an O2 sensor before and after the cat (or pair of cats, you can have up to four cats on a twin exhaust system).

1st make sure the O2 sensor isn't shot. If you used any non-sensor safe RTV or fuel addatives it might have coated the O2 sensor enough to trip the CEL.