Anti-foulers and CEL code P0420

[MI_Roger]

I installed a performance down-pipe on my Saab 9-5 nearly 45,000 miles and 2 years ago. I recently started receiving P0420 CEL codes (2 codes, nearly 2 weeks apart) indicating catalyst inefficiency and possible catalyst failure.

I have found a number of internet sites which advocate installing two anti-foulers to raise the rear O2 sensor out of the direct exhaust stream as a low cost method to eliminate this CEL. Lots of postings, most with short term follow-ups, but none yet with a long term follow up.

Has anyone here done this low cost mod to their rear O2 sensor and lived with it for an extended time? How is it for long term elimination of the CEL?

Thanks,

 

[beast3300]

It works, do it.

 

[jkhawaii]

p0420 means your cat needs to be repalced... that trick might work in theory because it would cause the o2 sensor after the cat to run cold and have little to no exhaust gas reach it. there are little piggy back modules that some people install on there cars when they remove the cats to also eliminate this code.

 

[db130]

it has been working for 2+ yrs for me. is that long term enough for you?

my car has the o2 sensors located before and after the PRECAT. when dying ignition coils caused gross misfires and took out the precat, i started to see the code, even though the main cat was unaffected. haven't seen the code since the antifoulers were installed.

 

[parimento1]

worked on my car!

 

[morris]

well i have herd of putting LOTS of methanol in the tank, it runs poor but will pass tailpipe sniff

 

[Chris142]

Where do you find antifoulers with the same threads and gaskets as an o2 sensor?

 

[beast3300]

Originally Posted By: Chris142
Where do you find antifoulers with the same threads and gaskets as an o2 sensor?


Autozone, 18mm by 1.5 in the HELP! section.

 

[MI_Roger]

Originally Posted By: db130
it has been working for 2+ yrs for me. is that long term enough for you?

Thanks! My car is 11 years old and I really don't want to spend $1200 for a new factory Cat, or $600 for another performance downpipe. Welding a new aftermarket Cat into the existing downpipe for a couple hundred dollars would be problematic - if not impossible!

 

[MyTQuick]

I put this stainless one on my Civic about a year ago. I cleared the code and it hasn't come back.

http://bigdaddiesgarage.com/straight-cel-fix.html

They also have and angeled adapter if space is an issue.

http://bigdaddiesgarage.com/angled-cel-fix.html

 

[brianl703]

The last post about something like this "vanished".

 

[MI_Roger]

Originally Posted By: MyTQuick
I put this stainless one on my Civic about a year ago. I cleared the code and it hasn't come back.

http://bigdaddiesgarage.com/straight-cel-fix.html

They also have and angeled adapter if space is an issue.

http://bigdaddiesgarage.com/angled-cel-fix.html


Perfect! I tried drilling out an inexpensive anti-fouler today and discovered the body shell is too small to allow drilling a hole large enough for the nose of the O2 sensor. These will work fine.

The irony is that when I drive my car hard, the exhaust system heats up enough to bring the Cat to proper operating temperatures. When I baby it (such as winter time roads in Michigan) the Cat doesn't always reach the proper temp. Hence the CEL only when driving easy, and then only some times.

Now which pollutes more? A working Cat on a hard driven engine using lots of gas and producing lots of exhaust, or a colder than ideal Cat on an easy driven engine? Tough question.

I can always install a second Cat in a straight length of exhaust behind the downpipe and extend the length of the O2 sensor wires (probably the best solution) but a $50 fix on an 11 year old car with nearly 300K miles seems to have a lot of merit. We don't have emisisons inspections here in Michigan, but if we did my car's age would likely make it exempt anyway.

 

[Vikas]

Are you required to have annual tailpipe emission tests? If so, they will fail with the anti-foulers. Well, actually they will fail because your converter is no longer working.

- Vikas

 

[ponderosaTX]

Quote:
Well, actually they will fail because your converter is no longer working.


Not necessarily. Most cars have two catalytic converters per cylinder bank: a small warmup cat in the exhaust manifold and a larger cat in the tailpipe for that bank. The downstream O2 sensors that flag P0421 (Bank 1) and P0431 (Bank 2) CEL codes only monitor the warmup cats. When the performance of a warmup cat falls below threshold, the OBD-II system does not have any information about how the corresponding main cat is functioning. Moreover, replacing the warmup cat to satisfy the OBD-II monitoring system has no impact on the performance on the main cat. So an OBD-II compliant car can have a non-functioning main cat.

Who knows what is coming out of the tailpipe? The OBD-II system does not measure it and neither do most state inspection protocols.

 

[bdcardinal]

They really do work. I bought an offroad downpipe for the Volvo and it actually has the extension built into where the cat monitor would go.