Several codes, just want to make sure my though process is right

[Dusten]

So I bought the car about 2 years ago. After about a month of ownership it threw a P0421 code. Going the cheap route I replaced the O2. Code never cleared but I kept driving it.
CEL has come and gone over the last 30k miles but came on recently and stayed. I pulled codes today and got P0421, P0302 and P0140
So my thoughts are, tune up. Replace the plugs and wires. Look for other causes of misfire on the #2 cylinder. Replace upper cat with a header(I care not about performance or sound, car is my DD and I commute 110 miles a day) and replace the down stream 02 and install a non fouler.

Or am I out to lunch on this topic?

Is there any large difference in headers in regards to quality?

 

[Jackie chan]

Sounds like a plan. Headers are kind of hit and miss, quality wise. You won't really find a great header nowadays unless one comes up used. Just grab a decent looking one off ebay, and hope the egr bung lines up.

 

[MrGiggles]

So I bought the car about 2 years ago. After about a month of ownership it threw a P0421 code. Going the cheap route I replaced the O2. Code never cleared but I kept driving it.
CEL has come and gone over the last 30k miles but came on recently and stayed. I pulled codes today and got P0421, P0302 and P0140
So my thoughts are, tune up. Replace the plugs and wires. Look for other causes of misfire on the #2 cylinder. Replace upper cat with a header(I care not about performance or sound, car is my DD and I commute 110 miles a day) and replace the down stream 02 and install a non fouler.

Or am I out to lunch on this topic?

Is there any large difference in headers in regards to quality?

I would leave the cat alone. I never noticed much of a difference with my headers, fuel economy or power wise. The exhaust sounds more like a trumpet now though.

Add coils to your tune-up parts list.

 

[smetzger]

P0421 - You replace the O2 sensor and the code didn't go away. Therefore your CAT is bad. You can either live with the code, replace the CAT, or drill out a spark plug non-fouler and put it in between the exhaust and the O2 sensor (google it, many posts videos on it).

P0302 - Most likely is a coil pack. But doing the plugs and wires isn't a bad idea.

P0140 - This sounds like a bad 02 Sensor. My guess is that the 02 sensor is clogged with soot since your CAT isn't working. I would do the non-fouler fix for the P0421 and knock any soot/crud off the 02 sensor and then clear the codes. If it comes back then get a new 02 sensor.

I actually had to put 2 non-foulers in my now wrecked 02 P5. I think the manual trans Protege's have more trouble with this.

Note: Once you clear your codes it is going to take a fair number of miles for everything to checkout. I have found that it the emissions stuff isn't working correctly or is barely within spec than it takes a long time (400 miles) to get a confirmed code or for a check to go from INC to OK. Look up the Mazda drive cycle and and least do the Stage 1 idle check to speed this process up a bit.

 

[Dusten]

thanks for the tips guys. Did the non fouler, used 2 just to be safe. found the 02 had come unplugged, so that explains that code.
replaced the coils, wires, and plugs. plugs didn't look terrible and still had correct gap, but I bet its been 30K since it was done, so its time.
Looked up the drive cycle and will start working on it. Will report on findings.

 

[Dusten]

Well either my new coils, plugs and wires have a miserable miss under 2k, or fixing these issues has caused the motor mounts to have the fact they have 200k on them to be amplified. The car has a horrible buck if i lug the motor under 2k in gear. I still have a CEL I need to go pull again.

 

[Dusten]

Replaced rear o2. Cleared codes. Been over 1000 miles, zero issues