P0421- Cat efficiancy code Pre cat

[north42g]

2002 Protege5 2.0L 107500 miles -
OBD II system reports DTC P0421-
I checked rear O2 sensor , its not lazy...I was hoping it was ...the Cat is Pricey!
Its the first one or Pre-Cat or Warm Up Cat.
Mazda Dealer wants $930.00 List and $740.00 Cost-even with my account I can't afford it.
Is there an aftermarket Cat that will work? With out triggering a another code in three months?!
Autozone has one for $320.00
NAPA has one for $318.00

What do you guys think?
Anyone Had any experience with this?

 

[mhrebin]

I just did the non fouler trick on the front o2 sensor and now my CEL is gone. I know it doesn't "fix" the problem but it makes me smile when I start the car up and see no CEL. lol

 

[tweety2300]

This depends if you have strict emission laws. You can do the non fouler trick and ignore the rotten egg smeel you will get. You can buy a header off ebay which will give you more power but you'll still have to do the non fouler. Also you do the non fouler on the 2nd o2 sensor if you do it on the 1st itl make your car run like s*** front o2 sensor controls the air fuel mixture 2nd o2 sensor just says if the pre cat is working

 

[north42g]

The "Non-Fouler Trick" ??? Where can thst proceedure be found? Somewhere on tyhis site I assume...
How bout just replacement of the Pre-cat?
Has anyone used an after-market one that works?

 

[Jordysoso]

Usually if someone has to replace it they just buy a header and do the non fouler trick bc it's cheaper than a new pre-cat. Use the search bar for the non fouler trick.

 

[north42g]

Ok so.... where do I get this said "non-fouler?"

Or should I just go with a Header- then I wont pass state emission inspections for sure.

 

[Jordysoso]

As long as you have the second catalytic convertor you will pass emissions. The header replaces the stock exhaust manifold and the pre-cat. Second cat is still intact. And use the search bar in the top right of the page to search for the non-fouler trick

 

[tweety2300]

It will fail if its cold so when you get it inspected make sure you take it and have them do it then

 

[visiongt9506]

non fouler FTW worked wonders on my 97 probe gt when installed my test pipe

 

[ponderosaTX]

Most states simply query the OBD-II System to check emissions equipment

On OBD-II equipped vehicles, the non-fouler trick generally works because most states query the OBD-II system to check emission equipment. If no MIL (CEL) codes are set and all of the I/M monitors are READY (or all but one in most states), then the vehicle passes the emissions test. In Texas, the inspection also includes a separate gas cap test.

When pre-cat performance falls below the threshold required by the OBD-II system, it does not mean that the exhaust smells like rotten eggs. Most Mazdas have two cats for each cylinder bank: a small one in the exhaust manifold and a larger one in the exhaust pipe for that bank. The small "pre" or "warmup" cat in the exhaust manifold is designed to reduce emissions while the main cat is still warming up. A marginal pre-cat may pass slightly more emissions through the exhaust system while the car is warming up.

When pre-cat performance falls below the required threshold, the status of the main cat is unknown because it not monitored by the OBD-II system. Moreover, its performance is not tested in most states. I have not seen the results of any tailpipe emissions tests on Mazdas with a fresh P0421 or P0431 MIL code. If any such test results have been posted on the web, I would appreciate a reference. My 2003 Mazda MPV has tripped P0421 MIL codes on a few occasions and I have never smelled rotten eggs.

The non-fouler trick has been discussed at length at mpvclub.com (which is currently down). All the reports that I have seen indicate that it works. You can eliminate drilling out a non-fouler by ordering an "O2 sensor extender" from ebay. An O2 sensor extender can be used in isolation (in place of a drilled out non-fouler) or in tandem with a non-fouler for a larger offset.

 

[north42g]

what does the non- fouler trick actually do in regards to measureing exhaust? is it measureing just clean air or what?

 

[digitalslacker]

Its pulling the o2 sensor out of the air stream from my understanding of it. It worked well for me for 15k miles till i replaced the engine.

 

[bigpturgeon]

The o2 sensor is measuring the quality of the exhaust, if it senses that its really dirty then it thinks that the the CAT is not doing its job and thus needs to be replaced. The nonfouler however tricks the o2 sensor into thinking that every thing is ok by restricting the amount of exhaust that actually gets to it.(doughpoke

 

[north42g]

Ok sounds good. Seems like it works for most. Iam thinking of installing a Header set. The CAT is starting to smell of roten eggs, And I don't care for it. Any way the Header would increase exhaust flow and give me a little bit more HP.
Can any of you recomend a cheap one that is decent. I'm not looking for el cheapo. But not creme de la creme either.

 

[WayneTeK]

i'm looking for one too, so if anybody has a cheap cat alternative, let us know!