Bad Cat

So my '94 Miata has failed smog 3 times now. Looking for the best option for a catalytic converter to pass smog.

Bit the bullet and took it to a shop to diagnose. They said the cat is bad (colder behind the cat than in front) Quoted me $280, labor included, to replace it. That seems reasonable, but I'm still poor.

I'm in CA, so finding a CARB legal cat online is tough. Looks like my best bet is this unit from Good-Win racing for $240+ shipping: http://www.good-win-racing.com/Mazda-Performance-Part/11-1033B.html

I don't necessarily need high-flow, since I can just take the old one and gut it to make a camouflage test pipe.

I can also borrow my dad's Cat off his '91. I don't know if that will fit though. Also, although that car passed smog, I'm not sure if his cat might still be a bit lazy, and if a lazy cat will even work for me. I borrowed another friend's cat that he said his car had passed with, and that caused my second smog check fail, apparently worse than with the cat on the car now.

Suggestions? I'm thinking I'll just bite the bullet and spend the extra $30 to have a shop do the work for me, unless their only way to put the cat on is to weld it.

that looks like a bolt in part. Shouldn't need welding to put in a new catalyst.

How much did you look at the results? Is the O2 sensor switching? Even if you changed it, is it switching?

oh, and what were the results?

It's interesting that live catalysts installed on your car don't work. Although, it's possible that the '91 cat isn't loaded like the '94 is.... but it's still interesting.

alfadriver wrote: that looks like a bolt in part. Shouldn't need welding to put in a new catalyst. How much did you look at the results? Is the O2 sensor switching? Even if you changed it, is it switching? oh, and what were the results? It's interesting that live catalysts installed on your car don't work. Although, it's possible that the '91 cat isn't loaded like the '94 is.... but it's still interesting.

I failed my HC's by a relatively minor amount. I don't have the sheet in front of me, but if I recall I'm allowed like 94ppm, and I produced 153ppm.

The O2 sensor is new as of a couple years ago. I have no idea how to tell if the O2 sensor is switching or not. The mechanic is pretty sure it's the cat. Says that it's cooler downstream, but should be warmer, since a functioning cat will produce heat from burning HCs.

The cat I'd put on that was supposedly good was off a buddy's '94. Since online stores seem to have different listings for 91-93 miata cats and for 94-97, I'm not sure my dad's would even work. I don't know enough about cats. I was guessing that they're something that isn't good/bad, but that degrades and works less well over time.

Prior to this last smog test, I changed my oil, refreshed the air filter, ran a tank with fuel cleaner through, and tried to take the car into the shop hot. It sat for about 10-15 minutes before going on the machine. The smog guy I go to is generally good at running cars on the machine for a bit to be sure the cat can get up to temp.

I know the cat I linked to from Good-Win is bolt-in. I was referring to whatever they put in from the local shop. The guy talked about welding it on, but at that time he'd presumed mine was welded on, since the car was too low for him to get up on his lift.

A good volt meter across the signal lines or from the signal line to ground should show you it going back and forth. When new, it will go from .2 to .8 V, roughly .5-1 hz at idle. When old, the voltages will get narrower, and the response will get slower. If it's a single voltage, something is wrong.

If you are just barely missing HC's but are passing NOx and CO (and I'd like to know those, too)- the cat may not be the culprit. But it very much depends on what HC, NOx, and CO all look like.

Before getting too far, post all of the numbers. I'll check the board tonight at home (if I remember).

Just spoke to the guy again really fast. He said he's 99.2% certain it's the cat. This shop has a good reputation.

If he does the work, he'll weld in the new cat on the flanges of the old one. $280 parts & labor + $40 diagnosis fee. I won't be able to use my old cat as a test-pipe though. I could sell it for scrap, or find some other flanges for it though. He will also pre-test the car for me so I'll know if that fixed it.

If I buy the part from Good-Win, I'm looking at $273 (part, tax, and ship) + $80 to the shop for their diagnosis. But I'll have a nicer cat, and my old unit to gut and use as a test pipe. But I don't think he'll give me the free test check to see if it passes.

If you don't need the high performance cat- $320 < $353. It probably won't add much anyway.

That's where I'm leaning. It would also be nice to have them test it before I go for my smog check again. If I do want a test pipe, I'm sure I can grab one off a craigslist partout.

I did send a quick message to Good Win racing about CARB rules for cats. They only talk about their cats being OBD II legal or not. If the regular ones are OBD I legal, I could spend only $175 for a standard cat. So, $255 total.

Why do you think you need a test pipe? GRM's article on catalysts, performance, etc- showed that the test pipe was less than good. Most of the catalyst set ups, inlcuding OEM, made better power.

oh, and you are OBDI for sure.

If you want to see IF you can do it, jack it up, and see if you can loosen all 4 bolts. If you can- it's a straighforward swap. Especially since $255< $320. Although, does the shop install include post testing, or is that just assumed? Or do you have to post test after you do the work?

From experience test pipes on Miatas slow the cars down.

The cat on there is bolt in. I can do the work myself. The Miata has to go to a test-only station, but I already paid once, and have a free retest. The shop will just do a test after doing the work, to be sure the problem is fixed and I can go pass my re-test no problems.

If I order the cheap one from Good-Win, it probably isn't CARB certified. I'm not sure that really matters though. The car is too low for them to look for any CARB stamp, and it aught to make the HC problem go away.

Or, I order the part and have him install and test it, since the $80 fee gets applied to any repairs they have to do. They're not making any mark-up on parts.

Okay. Got ahold of Good-Win. Although their every-state-but-CA units would almost certainly get me to pass at any shop that doesn't look really closely, they will not even ship them to a CA address. Which means their cheapest option would end up being $353. I'll have the shop do it for $320 (actually a bit more for tax), and it will get tested and be ready to go tomorrow.

I was sure that this post was going to be about this.

Buffalo police find cat marinating in car trunk

My dad had a muffler shop cat put on his subaru, and it failed again less than 6 months later. The car does have a ton of miles on it and burns oil, but the last 2 cars he had with the same mileage still had the original cat. A factory subaru one is $1700 though, so if thats the only option it may get replaced with something that is cheaper to get parts for. So be glad you dont have an OBD II subaru, $320 is a bit, but it could be worse. lol

Travis_K wrote: My dad had a muffler shop cat put on his subaru, and it failed again less than 6 months later. The car does have a ton of miles on it and burns oil, but the last 2 cars he had with the same mileage still had the original cat. A factory subaru one is $1700 though, so if thats the only option it may get replaced with something that is cheaper to get parts for. So be glad you dont have an OBD II subaru, $320 is a bit, but it could be worse. lol

No kidding. And driving the Miata will save me a lot on gas over driving the van, since I average 25-29mpg instead of 14-16mpg. Borrowing the hard top from my dad's car that's under long-term repairs has gained me 3-4mpg. So I figure, $50/month, plus I'm having more fun.

John Brown wrote: From experience test pipes on Miatas slow the cars down.

Here's a thing though, could it potentially extend the life of this new cat that I've paid good money for? Is flogging the car mercilessly at the track shortening the life of my cat? I know they run rich at high RPM. Is the cat getting over-worked having to deal with those extra HCs?

From what I recall of the GRM test, the test pipe didn't help over a good high-flow cat, but it didn't hurt. And they both gained 1-2hp over a regular cat. Which isn't big, but it's a bit.

I'm so glad i'm not in CA anymore. $89 magnaflow hi flow cat works for me.

I've read a lot of stories like yours from the other side of the inspection table. Generally, the story goes like this: "This poor cheap SOB bought the cheapest cat he could find, and it wouldn't pass the Cali test. He took it back to the backyard where it was worked on, and installed a name brand aftermarket cat. When it still failed, he gave up, I kept the car and installed the factory cat, after which it passed with flying colors."

Also- find a good shop. To condemn a cat based upon inlet and outlet temps is backyard. You need someone who can tell you exactly what the numbers are, and what they mean.

Streetwiseguy wrote: I've read a lot of stories like yours from the other side of the inspection table. Generally, the story goes like this: "This poor cheap SOB bought the cheapest cat he could find, and it wouldn't pass the Cali test. He took it back to the backyard where it was worked on, and installed a name brand aftermarket cat. When it still failed, he gave up, I kept the car and installed the factory cat, after which it passed with flying colors." Also- find a good shop. To condemn a cat based upon inlet and outlet temps is backyard. You need someone who can tell you exactly what the numbers are, and what they mean.

Well, it's kind of a done deal now. I've told the mechanic to replace the cat with the one he intended. The smog test station (who I like) did say this was a good shop that would get the car fixed and able to pass.

He was able to tell me what the temperatures were, I just don't remember. If you're referring to my smog test numbers, I brought him the numbers from the test-only station.

I think the proof will be what it does with a new cat.