First day out in my "New" Miata and got a P0420

I'm crushed. I finally got everything I need to get my 1997 Miata drivable: inspected, insurance, title, registration, plates and tolltag. First time on the road today and CEL comes on. About 50 miles into it I was able to swing by the house and hook it up to my OBD to get the code. When I read the description I felt like I swallowed a brick...

Background: This is my second Miata. I got it after my BMW Z3 suspension went wack after hitting some high tracks over by Frys/Bush tollway in Plano. So I took my precious week of vacation to replace all the suspension and rubber on it, bought this Miata to be my new daily driver, and planned on keeping the Z3 as a second. Didn't at all plan on having issues with the Miata too so early on.

Bought the car a week ago for $6300. Car belonged to an elderly lady who passed away and it had been sitting for about 1.5 years. 1997 with 33K miles. Z3 has a similar story and never had any major issues with it for 9 years.

The car just passed inspection so I'm doubting the code a bit, but since it was sitting for a while I can't rule it out. I reset the error but it returned in about 30 miles.

The car was clearly well maintained and with such low mileage, well I just wasn't expecting to have to deal with another sick car this "vacation" week.

I read in this and other forums that it won't hurt anything more to drive it, and I have little choice since the other car will be disassembled tomorrow. I read that spark plugs might make a difference? I also noticed what may be a source for vacuum leak, possibly around the EGR.

Thing is, if the Cat really is dead I need to fix whatever caused it before I just go and replace it.

I'd appreciate any suggestions, advice, commentaries, testimonials here. I also see http://www.bigdaddiesgarage.com/mini-cat-cel-fix.html as a possible option. Been years since I turned a wrench in any serious capacity.

Lastly, any mechanic recommendations in the North Plano area? I'm at Spring Creek and the NDallas Tollway.

Thanks!

Oh one other note. The inspection required a new gas cap to pass. Since I wanted it to pass w/out another trip I bought their cap for $20. It was too tall so I pulled the O ring out of the new one and put it on the old one. Could a bad cap cause this?

Could be a bad O2 sensor. Plenty of P0420 threads if you search for them.

Track Dog Racing is up in the neck of the woods if you want to bring it somewhere.

Welcome aboard.

Can your scanner graph live OBDII engine data?

>Can your scanner graph live OBDII engine data?

Yes it can, perhaps a bit limited on the handheld but I can also run it on a laptop (bluetooth connection). I capped a little of it. What am I looking for?

Thanks!

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Originally Posted by sammm

Could be a bad O2 sensor. Plenty of P0420 threads if you search for them.

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Yeah, found several but not on a car with so few miles. Sensor is a possibility but they're expensive too. Would rather find a definitive cause if I can.

I peeked around for about an hour looking for the ever illusive "on/off switch" that would fix the problem and was kind of surprised with how well laid out things are in terms of accessibility. I think this may be the most workable motor I've seen in a long time. Sorry I didn't get more acquainted with my M Edition. I can even access the spark plugs! I went ahead and checked them and they looked pretty good. No oil and no pitting. Wires look good.

It appears that clearing the fault code, albeit temporarily, the car resumes normal operation. I read somewhere that a cat fault causes the car to run in some kind of low performance mode, which explained why it seemed so slow earlier today.

Quote:

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Originally Posted by sammm

Track Dog Racing is up in the neck of the woods if you want to bring it somewhere.

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Duly noted. I'm hoping I can resolve myself because...$500 makes me sad ;)

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Originally Posted by sammm

Welcome aboard.

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Hey, I resumed looking up info and this site http://www.obd-codes.com/p0420 states

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Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe

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I noticed quite a clatter when the car is in drive (automatic) with the A/C on. Sounds more like a waggly heat shroud but might be worth taking a look. Prob for me is I already have my week tied up on the Z3 suspension. Blech...

Quote:

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Originally Posted by Sangatster

The inspection required a new gas cap to pass. Since I wanted it to pass w/out another trip I bought their cap for $20. It was too tall so I pulled the O ring out of the new one and put it on the old one. Could a bad cap cause this?

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Yes, get the proper parts before proceeding to replacing more expensive parts that are likely unnecessary.
http://prioritymazdaparts.com/gas-cap-nb38-42-250/

Quote:

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Originally Posted by Sangatster

>Can your scanner graph live OBDII engine data?

Yes it can, perhaps a bit limited on the handheld but I can also run it on a laptop (bluetooth connection). I capped a little of it. What am I looking for?

Thanks!

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It has been a bit since I messed with it. But I found a bunch of good stuff on the YouTube when I was messing with this issue with one of my other ford/mazda products.

Basically you want to see the "correct" waveform on both sensors.

Well, I confirmed, the cat is dead. I mentioned yesterday that instead of purring I was hearing a clatter, yeah, well that was from little chunks of cat rattling around inside the cat box. Got under the car this evening and gave her a few pats and it sounded like rocks in a soup can.

I recorded it on my phone and will upload to youtube later since I don't think these forums accept vids. Just to show what a rattlecat sounds like.

Now the next question is, why did it fail? Old gas comes to mind, but would it cause the cat to blow chunks so bad? And so quickly. The car just passed inspection last week. I'm apprehensive about installing another cat if there's a chance this one is going to die too.

Per sammm's recommendation I'm going to hit up Track Dog. They have a Magnaflow cat for under $150 that they sound pretty confident about.

Besides getting the bolts off (exhaust bolts can be exhausting..har) it doesn't look difficult. New gaskets, pop in and out. Any warnings?

Thanks!

4 bolts, nuts and washers, 2 gaskets. Easy DIY.

Sweet. I'm going to pick up the cat then work on the Z3, give the Miata time to chill. Thanks, fellow cheap bastard.

May not hurt to soak the rusty nuts and bolts with Kroil before ya get to wrenching!

https://images-na.ssl-images-amazon....1mevS3pCbL.jpg

^This! If they are crunchy enough, do yourself a favor and get new hardware for the new cat.

Uploaded a highly scientific approach to determine if there is an issue with your catalytic converter: https://www.youtube.com/watch?v=J1aH9jXaRPs

Went to Track Dog today and picked up a new cat. Came with gaskets and hardware (nuts, bolts). OEM is larger, this one has more pipe, less chamber. OEM also nicely had bolts brazed on so only one wrench required and I think the bolts were brass so no rust. But for about $160 total not too bad. Easy job. Rattle gone, now just need to see if CEL is gone for good.

Just a closing comment. It's been a couple weeks since I installed the replacement cat I picked up at Track Dog Racing. Check engine light never returned. Installation took me about 45 minutes to do it in the parking lot in the dark, and I took my time.

The cat I got at Track Dog Racing is smaller overall (same length, more pipe, less canister) but seems about the same as the OEM.

Thanks again everyone!

I like you signature. Check this thread out...http://www.dfwmiata.com/threads/1293...ghlight=binary