Chris(MA)

Throwing a CEL for low efficiency on bank 2. I reset it a couple of times and it comes back, my car uses zero oil between changes so not contamination etc

I think at 112k miles they are toast.

What are my options? Should I bother with changing the O2 sensors? I have a borescope so maybe I should snake it in and look at the condition of them inside?

I'm in California so have to pass smog in a few months, I don't want to pay $$$ for OEM. I will keep an eye out for used cat's on local ads with lower miles.

I also considered cutting the cans open and welding in some new universal cat elements, anyone done this? I have a 2000 996.1 all stock.

Ahsai

NuttyProfessor

I've been having the same problem. My remedy?... lots of "cat food". hahaha Yep, I been feeding it two cans of seafoam, and the CEL went away. If this doesn't work in the long run, I may have to replace the catalytic converters, but I'm hoping to wake up my dead cat! Those darn cat converters are crazy expensive!

Imo000

Try swapping the downstream O2 sensors from one site to the next. If the code follows the sensor you have your answer. If it doesn't, you'll have you answer too.

808Bill

Are you using seafoam through the intake?

cds72911

I'd probably start with the O2 sensors, they're cheap enough to be worth doing, whether you continue to use your current cats or replace them.

I'm a fan of sport cats. I've had 200 cell on both my 3.4 and my 3.6 and they're great, they seem to have a seat of the pants improvement in performance (full disclosure: I've never dynoed my car, so I have no idea whether there is any actual improvement). A thing you might need to worry about is CARB certified or original equipment in CA - I don't have the same issues in VT, so don't know anything other than what I've read about the Republik of Kalfornia emissions regs.

Chris(MA)

Actually one idea I had was to pull the cats off, scope them to make sure the ceramic core hadn't actually collapsed or somehow been mechanically destroyed then if all looked ok I would try washing them with MEK (methyl ethyl ketone). Its a really good solvent for washing away any nasty organic residue, I figure its worth a shot.

It will do zero damage to the ceramic or metallic element, its only an organic solvent. In a best case it washes away enough gunk on the cat to up its efficiency enough to clear the code. My wife has loads of MEK at her work so I could get it from her.

Also good idea for trying to swap the O2 sensors from the banks to see if the code follows, I can try that this weekend.

EDIT: looks like acetone might work better

Ahsai

It's possible the cat element inside has come loose, in which case you may be able to open it up and re-weld the element.
Once the cat is off the car, you can shake it and you will be able to see and feel if the element is loose.

danielcooper9

Ahsai, Can you elaborate on your experience with Carnewal's 200? Can' t remember where you live but you don't have problems with emissions test or cel's? You ship them over to Belgium, if so do you remember costs (I haven't contacted gert about that)? Looks like a really inexpensive option if someone could live with the time it takes to rebuild

Ahsai

Sure. i have a thread here.

5yrs and 26k miles later still working well and passing smog (OBDII style smog check, not tailpipe. Not saying it won't pass tailpipe test though)

jimham968

808Bill

Reverse flush if you go that route.

NuttyProfessor

No, I don't add to the intake. Mix with the gasoline. I usually put 2 cans of seafoam in a 1/4 tank of gas, drive it hard for about an hour, and then refill with top tier gasoline.

808Bill

I see they have an aerosol spray for the throttle body. I wonder how well that works?

mrjonger

That's what happened to mine. The element is loose and I can hear / feel it moving around. I've been contemplating between going with Carnewal or just re-welding the original element - which only has 36K miles on it.

In the meantime, I bought a cheap set off RLister. Chris, if you're interested in cheap OEM replacements (I think they have 80Kish miles on them), I'd be willing to fix my original set and sell you the pair that I bought at what I paid. PM if you're interested, it will be your cheapest option by far and I believe you're close to me - I'm in South SF.