Bad (pre) Cat

[SouthATX]

I have been getting the P0421 CEL code, and have changed the coils, plug wires, lower 02 sensor and it still comes back. I see that Rockauto offers the Walker replacement precat (part #16220) for the P5, but the muffler shop - a Walker dealer - I called said Walker doesn't offer one, and blah, blah, blah, I need to buy something else for $800. Has anyone used this model from Walker? It looks like it should work. I am going to try the defouler how-to to get the CEL light off, but need a back up plan in case I have trouble at the emissions test. BTW- I don't live in CA.

Thanks!

 

[ucMP3]

Don't buy an oem replacement cat. $800 is a lot of cash... Honestly, I would buy a cheap header if I were you, but you can find a pre cat from someone here on the this board, or at a junkyard for under $100.

 

[nickster]

I have been getting the P0421 CEL code, and have changed the coils, plug wires, lower 02 sensor and it still comes back. I see that Rockauto offers the Walker replacement precat (part #16220) for the P5, but the muffler shop - a Walker dealer - I called said Walker doesn't offer one, and blah, blah, blah, I need to buy something else for $800. Has anyone used this model from Walker? It looks like it should work. I am going to try the defouler how-to to get the CEL light off, but need a back up plan in case I have trouble at the emissions test. BTW- I don't live in CA.

Can't go wrong with $113.05 http://cgi.ebay.com/ebaymotors/Mazd...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

 

[ucMP3]

Can't go wrong with $113.05 http://cgi.ebay.com/ebaymotors/Mazd...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

^That looks like a pretty good route to go...

 

[SouthATX]

excellent - thanks!!

 

[dpmarc]

excellent - thanks!!

I have been getting the same code, but as I understand it, that code will sometimes come up first because of another part is failing. I would def buy a header or check your junkyard. I also found pre CATs on ebay for around 100$

http://cgi.ebay.com/ebaymotors/Mazd...rQ5fTruckQ5fPartsQ5fAccessories#ht_1132wt_921

Marc

 

[ucMP3]

I have been getting the same code, but as I understand it, that code will sometimes come up first because of another part is failing. I would def buy a header or check your junkyard. I also found pre CATs on ebay for around 100$

http://cgi.ebay.com/ebaymotors/Mazd...rQ5fTruckQ5fPartsQ5fAccessories#ht_1132wt_921

Marc

Something like that... The other part failing can lead to the cat being destroyed over time. This other part is often the primary O2 sensor. There are other things that can cause your cat to fail tho.

 

[P-Funk!]

^x2.

 

[slavrenz]

Can't go wrong with $113.05 http://cgi.ebay.com/ebaymotors/Mazd...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

DO NOT BUY A CAT OFF OF EBAY! I got screwed over on one I got a few years ago for my pre-cat for about the same price. The ebay seller had a good feedback rating, and the cat was a direct fit, but it only lasted a few months.

Seriously, Muffexpress is the seller's name (doesn't exactly yell professional to me)! For all you know this guy is importing some cheap Chinese-made crap that goes bad just after the buyer posts a positive review.

The Walker unit is quality, and I've been using it on my car for about a year and a half now with no problems. It comes with a 5 year, 25,000 mile warranty, and the people who work at the company are knowledgeable and accessible (I called to ask if the top flange bolts are included with the cat, and they are).

Also, did you notice that both of those "no-name" ebay cats are shipping from Toronto? I bet the low-lifes have several user profiles set up, so that if one gets hit with negative feedback, they can fall back on the others.

In short: don't buy an exhaust part from a company you've never heard of. To the more senior members who have given their approval thus far, you ought to know better.

 

[slavrenz]

I have been getting the same code, but as I understand it, that code will sometimes come up first because of another part is failing. I would def buy a header or check your junkyard. I also found pre CATs on ebay for around 100$

http://cgi.ebay.com/ebaymotors/Mazd...rQ5fTruckQ5fPartsQ5fAccessories#ht_1132wt_921

Marc

This code usually comes up because people get misfires due to bad ignition coils, and our cats are really sensitive to being contaminated with unburnt fuel. The only other things to cause this code would be an exhaust leak before the cat and a bad rear O2 sensor.

If your front O2 sensor is bad enough to damage your cat, you will get another code for this before you get the P0421 code.

 

[Tzar177]

DO NOT BUY A CAT OFF OF EBAY! I got screwed over on one I got a few years ago for my pre-cat for about the same price. The ebay seller had a good feedback rating, and the cat was a direct fit, but it only lasted a few months.

Seriously, Muffexpress is the seller's name (doesn't exactly yell professional to me)! For all you know this guy is importing some cheap Chinese-made crap that goes bad just after the buyer posts a positive review.

The Walker unit is quality, and I've been using it on my car for about a year and a half now with no problems. It comes with a 5 year, 25,000 mile warranty, and the people who work at the company are knowledgeable and accessible (I called to ask if the top flange bolts are included with the cat, and they are).

Also, did you notice that both of those "no-name" ebay cats are shipping from Toronto? I bet the low-lifes have several user profiles set up, so that if one gets hit with negative feedback, they can fall back on the others.

In short: don't buy an exhaust part from a company you've never heard of. To the more senior members who have given their approval thus far, you ought to know better.

I bought this from the same seller back in the summer and i've had no problems http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=200337790227

 

[slavrenz]

I bought this from the same seller back in the summer and i've had no problems http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=200337790227

(squinty)

That's because there's no oxygen sensor behind this one to monitor it, like there is the precat - there's no way to know if it's working properly unless it breaks up and plugs your exhaust (then you'll definitely know it's not working).

 

[protegedude25]

ok fellow mazda owners this code has been coming up on everyones car so i though i test out the non-fouler deal!!!!!!!!!! and to my knowledge it actually worked so protege owners with this p0421 code just install a non-fouler simple as pie it will solve the problem right away and as for buying a cheap header from ebay idk were the part cheap comes in to play but i bought one for 80 and damn this b**** hasn't broke or anything works fine for me and for the cat i bought 3 already for all my cars they work badass to for 30 bucks eash i aint mad and if you got problems u might wanna sea foam your car cause it aint the cat its all that carbon building up.(my opinion)

 

[protegedude25]

I bought this one for my protege but I bid and got it for 30 but it works great

http://cgi.ebay.com/ebaymotors/Magn...r_Truck_Parts_Accessories?hash=item5ad4f24f1e

as for header this is the one i got had it for almost 5 months no problem at all im paying for header not the name on the header

http://cgi.ebay.com/ebaymotors/Race...r_Truck_Parts_Accessories?hash=item2a0349cc4f

 

[slavrenz]

ok fellow mazda owners this code has been coming up on everyones car so i though i test out the non-fouler deal!!!!!!!!!! and to my knowledge it actually worked so protege owners with this p0421 code just install a non-fouler simple as pie it will solve the problem right away and as for buying a cheap header from ebay idk were the part cheap comes in to play but i bought one for 80 and damn this b**** hasn't broke or anything works fine for me and for the cat i bought 3 already for all my cars they work badass to for 30 bucks eash i aint mad and if you got problems u might wanna sea foam your car cause it aint the cat its all that carbon building up.(my opinion)

So if your opinion is that the P0421 is caused by carbon buildup, I hate to say it, but that is wrong. Without getting too much into the technical details, yes seafoam is good, and yes, the nonfouler will get rid of your CEL, but if your state has emissions testing and you've got the P0421 code, you're gonna have to install a reputable cat.

 

[slavrenz]

I bought this one for my protege but I bid and got it for 30 but it works great

http://cgi.ebay.com/ebaymotors/Magn...r_Truck_Parts_Accessories?hash=item5ad4f24f1e

as for header this is the one i got had it for almost 5 months no problem at all im paying for header not the name on the header

http://cgi.ebay.com/ebaymotors/Race...r_Truck_Parts_Accessories?hash=item2a0349cc4f

This is a universal converter, and will not work in the current location of the front cat (you need to weld this in, and you can't weld to the cast iron exhaust manifold, as far as I know).

Exactly how did you attach this?

 

[protegedude25]

huh ^ i said if your cat keeps going bad then u must have alot of carb i never said it makes ur p0421 cell come on all this code is saying is that your to rich and installing fouler will lean u out cause it moves o2 back which tell the computer to lean you out all im saying if you want you cell to go away and dont wanna buy the 150 o2 do the nonfouler idea i passed my emissions test easy

 

[protegedude25]

This is a universal converter, and will not work in the current location of the front cat (you need to weld this in, and you can't weld to the cast iron exhaust manifold, as far as I know).

Exactly how did you attach this?

custom exhaust no need to be technical lol no muffler not piping new resonator new everything old exhaust sucks ill take pics tomorrow i mean for 75 bucks s*** they did a badass job on my exhaust but for u there is another one that bolts up that i was going to get before this one but it cost like 160

 

[StealthWyvern]

If you have a bad cat you have or had other issues to make it go bad... I think I still have my pre-cat from my old p5 in storage. I can dig around and see if I can find it some time tomorrow if you would like. However the thing is decent sized and I wouldn't know how to go about packaging it for shipping either.

 

[slavrenz]

huh ^ i said if your cat keeps going bad then u must have alot of carb i never said it makes ur p0421 cell come on all this code is saying is that your to rich and installing fouler will lean u out cause it moves o2 back which tell the computer to lean you out all im saying if you want you cell to go away and dont wanna buy the 150 o2 do the nonfouler idea i passed my emissions test easy

First of all, please don't type one giant run-on sentence. It is very difficult to read, and makes it hard to take your comments seriously.

Secondly, the code P0421 does not mean that your car is running rich - it means that your catalytic converter is bad. There's not really any other way to argue this, other than me pointing you to the page in the repair manual that directly states this.

I maintain my original statement that carbon buildup alone will not cause this code to be set, since carbon will virtually never get down that far in to your exhaust in large enough quantities. Installing a nonfouler will not lean you out, since the rear O2 sensor readings do not control your air/fuel ratio - it is only there to monitor the performance of your catalytic converter. The nonfouler will only move your rear O2 sensor further out of the dirty exhaust stream, making it seem as if your catalytic converter is working to clean your exhaust (but it's not really). As for passing your emissions test, if you have a rear cat, then this may clean your exhaust well enough to pass.

In your case, you installed a new universal catalytic converter, so I'm not surprised that you passed your emissions test. For the OP (Original Poster), he may or may not pass if his state does tailpipe testing and he's only got one good cat.