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Discussion Starter #1
Looking for some help making a decision on keeping the car -

1999 Millenia S w/ 85k miles
One owner, no accidents
Lived its life in Georgia, mostly garaged, no rust, good paint
Well maintained, with all hoses, fluids, CV axles, and tires replaced in last 2 yrs. Everything works.
Pioneer CD/USB/BT single DIN head unit with Kicker speakers in stock locations

Has the dreaded P0421 code now, indicating exhaust pre-cat needs replacing. I'm guessing it's a $1k fix, with some chance that the other bank pre-cat could also fail anytime in the future. (I don't have access to a lift or air tools so fixing it myself would be difficult to impossible.)

Any opinions on current, unrepaired value?

Thanks
Mike
 

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haveing just replaced the 02 sensors i dont thingk replaceing the headers and cat will be that hard.
for the front would be a good idea to remove the radiator fans. this opens up alot of space to get your tools in there.
and for the rear u need the front of the car on stands and just try to get up in there. a hoist would help alot but required.

I dont really find these cars that difficult to work on. yes there is limited space but once u remove what ever is in the way all u really need is basic tools to get the job done.
I find various sizes of sockets and extensions and swivel sockets highly valuable.
 

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yah, well, replacing the o2 sensors is a walk in the park compared to the precat. and the one on the rear bank, to boot. i have done it twice. i would NEVER attempt it without a lift. everything has to come off from underneath. and i mean the entire exh system. it is like a giant puzzle. one part dont come off unless the connecting part comes off first, and that one dont come off unless the other connecting part comes off first, etc, etc. then, getting that sucker out of there was a chore. the first one, my friend, who owns the shop where i took the car to use one of his lifts, got it out. i was about to drop the jack shaft for clearance. i fought it for about 20 min, and he comes over, looks at it for a bit, then turns it and out it comes. one good thing about mazda, they use a LOT of alloy fasteners for the exhaust, and they dont rust. and they aint magnetic, so if you drop one, you better find it. here is what i would do. either do the anti fouler trick, or the resistor trick, and call it a day. the one caveat is that if you sell the car, in some states, if the car dont pass inspection, they can make you buy it back. and if you do the anti fouler or the resistor trick, you have tampered with the emissions, and if they find out, you could be in trouble. beware of that place in canada who sells aftermarket precats. the one i got would not quite line up, and if all the bolts are torqued down, it will bend the pipe. on both cars, i could tell they ran better after changing the precat. now, the front one is pretty easy, but i know i pulled the radiator for more clearance. if you plan on keeping the car, i THINK that if you buy all 3 pieces from the canadian company(both precats and the Y pipe), the assembly will bolt up to the rest of the exhaust. while you are under there, think long and hard about changing the rear motor mount, you can get to it then. as far as value, a 99 with a cat code i would be surprised if you got more than 500 for it. we have 2 99's, one we bought new. on both cars, i have changed out radiators, all the cooling AND breather hoses, including the oil cooler hoses, valve cover gaskets, axles, ALL the links and the control arms, both front and rear, and tie rod ends, rack boots, p/s pumps(THAT is a sob job, too), water pumps, buncha timing belts, vacuum lines, solenoids, steering column on one car(another sumbitch job), steering tilt motors, shock absorbers front and rear(another sob job), and a whole lot more. i like the cars, they are very well made. we dont drive a lot, and they are now like a hobby to me. and i also have a lot of special tools. i recently got rid of my air compressor, and i have gone to cordless tools, which are a big improvement over air tools.
 

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Always appreciate a good post by you Keninn. I have thought about the rear manifold job myself and will push it off as long as possible. I just used a non fouler as Keninn mentioned to prevent to code from coming up. Unless it's clogged I'm not worried about it. But I bet there would be a little more power if I could gut those precats.
 

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Discussion Starter #5
As always, thanks for the reply, Ken. I appreciate your willingness to help so many people on the forum here.

I had a feeling that it wouldn't be worth the trouble to fix. It is frustrating because, as you say, the Millenia is overall a well-made car. I guess it can't drop in value much more. I've got another 9 months before annual emissions check. That may be the time to dump it.
 

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There are ways to get around the code without actually replacing the cat converter. If the car overall is good, I would go that route and get it to pass the check. I have read that there is also an additive to the gas I think that is a sure pass. It essentially is fooling the computer in the amount of miles it takes for the computer to be in ready mode and pass for you. I would have a hard time sending an overall well kept Milly to the U-pull.
TomK
 

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There are ways to get around the code without actually replacing the cat converter. If the car overall is good, I would go that route and get it to pass the check. I have read that there is also an additive to the gas I think that is a sure pass. It essentially is fooling the computer in the amount of miles it takes for the computer to be in ready mode and pass for you. I would have a hard time sending an overall well kept Milly to the U-pull.
TomK
if you mean cataclean, i tried it, and no workee for me. i have a 2002 outback i use for my part time job at the usps. i ended up changing the cat and the pre and post o2 sensors. however, against all posts i had read about NOT using a denso post cat sensor on the subie, i used a bosch. after initial install of the cat, i still got the cat code. just to be sure, i changed the bosch to a denso, and the code has never returned. now i am wondering if i only needed to change the sensor. visual inspection of the old cat appeared to be still in excellent condition.
 

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I'd keep the car, you know you'll regret it if you get rid of it. In my state many extensions are provided for emissions through various means, might be something to look into.
 

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Use a non-fouler.

If you want to check the pre-cats, you can use an exhaust back pressure tester.

The gauge has an O2 sensor fitting that you remove the O2 sensor before the pre-cat, and screw the tester into that fitting. You have to do this twice, once for each pre-cat.

Then, to test the back pressure:

- At idle, it is suppose to be 1 psi or less.
- At 2,500 rpm it is suppose to be 2 psi or less.
- When doing a "snap throttle" test, it shouldn't jump up to more than 2.5-3 psi. (Be at idle, and snap the throttle to about 4,000 rpm quickly).

If readings are at or below this, your precats are fine and not clogged. If the readings are above this, that indicates a clogged pre-cat.

If the precats are clogged, you could also gut them and use non-foulers after the precats. The main cat on the Millenia is large and does most of the work, and the pre-cats do little. So with gutted pre-cats and a good main cat, you should pass inspection. Or just put a gigantic oversized aftermarket main cat to suck up all that bad stuff.

See this post:

http://forums.mazdaworld.org/100-millenia/94706-exhaust-back-pressure-test.html

Buy this item from Amazon:

http://www.amazon.com/Tool-Aid-33600-Exhaust-Pressure/dp/B0002SQW9S/ref=sr_1_1?ie=UTF8&qid=1442005713&sr=8-1&keywords=exhaust+back+pressure+tester
 

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Discussion Starter #10
Good info. Thanks, mazda-fla.

I guess there's a chance that my recent fuel mileage drop of about 2 mpg could be due to a clogged precat. The engine also doesn't seem as strong under heavy throttle either.
 

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Discussion Starter #11
Btw, I stopped by the local CarMax store on the way home tonight. Their offer was $1000 with full disclosure of the CEL issue.
 

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Is that price to replace the pre-cat with the issue or just to get the car to pass the smog test. And what does a full disclosure of the CEL issue mean? I would bet that anyone there working at CarMax has never worked on a Millenia S or even seen a Miller Cycle engine.
TomK
 

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Discussion Starter #13
No, that would be the price CarMax would pay me for the car, which they would send off to an auction. I don't think they do actual repairs at CarMax, just buy/sell cars.
 

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Discussion Starter #16
Yeah, that's not much money.

My other consideration is that keeping the car will cost me an additional $125/month for insurance when my son gets his license next month. It's a 3rd car and we could live with 2.
 
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