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post #1 of 24 (permalink) Old 02-22-2019, 12:36 PM Thread Starter
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New-to-me 07 S V6 CEL P0431

Hi everyone, I am the new owner of a 2007 V6 3.0L S Sedan. I bought it for moderately cheap as it had been sitting for a while and when I test drove it, probably need a wheel bearing and a transmission fluid change (whirring noise, fluid is darker than it should be but not black). As I drive it 40mi home, CEL turned on after 10mi or so. Stopped into Advance and they identified it as P0431. Doing some research on here it looks like it is a bad pre-cat, radiator side. I think it's
the cat and not an 02 sensor because It's louder than I think it should be, and I can smell exhaust in the cabin. I would like to do this fix myself but I've read that a bad precat can lead to engine failure from the EGR sucking up bits of the cat into the cylinders. I am by no means a mechanic, but I'd like to know how I can tell if this has already happened. Since i just bought the car, I don't really know if it's down on power, it doesn't seem to be, just going off of feel, but I'd like to do as much preventative maintenance as possible while replacing the cat. Does anyone have any advice or tips for proceeding? I haven't driven it since I got home and parked it that night.

thanks
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post #2 of 24 (permalink) Old 02-22-2019, 02:28 PM
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New-to-me 07 S V6 CEL P0431

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Originally Posted by [email protected] View Post
Hi everyone, I am the new owner of a 2007 V6 3.0L S Sedan. I bought it for moderately cheap as it had been sitting for a while and when I test drove it, probably need a wheel bearing and a transmission fluid change (whirring noise, fluid is darker than it should be but not black). As I drive it 40mi home, CEL turned on after 10mi or so. Stopped into Advance and they identified it as P0431. Doing some research on here it looks like it is a bad pre-cat, radiator side. I think it's
the cat and not an 02 sensor because It's louder than I think it should be, and I can smell exhaust in the cabin. I would like to do this fix myself but I've read that a bad precat can lead to engine failure from the EGR sucking up bits of the cat into the cylinders. I am by no means a mechanic, but I'd like to know how I can tell if this has already happened. Since i just bought the car, I don't really know if it's down on power, it doesn't seem to be, just going off of feel, but I'd like to do as much preventative maintenance as possible while replacing the cat. Does anyone have any advice or tips for proceeding? I haven't driven it since I got home and parked it that night.

thanks


If the bad cat is on the radiator side you should be in the clear, the egr pulls from the back cat. If youre getting in there you really should replace all 3 of the cats so you dont have the problem that @DrFeelGood had, he replaced the precats only and ended up having to do it a second time because his secondary cats were ruined which in turn destroyed the new precats. One way to tell if you have been sucking cat material would be to remove the intake manifold and see if there are white specs in there, but unless the car is down on power and sucking obscene amounts of oil you are good.

For preventative maintenance I would replace the plugs/coils change the atf (you said 07 so your ATX should take ATF T-IV) ASAP you might also want to replace the PCV valve


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post #3 of 24 (permalink) Old 02-22-2019, 02:52 PM
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Quote:
Originally Posted by [email protected] View Post
Hi everyone, I am the new owner of a 2007 V6 3.0L S Sedan. I bought it for moderately cheap as it had been sitting for a while and when I test drove it, probably need a wheel bearing and a transmission fluid change (whirring noise, fluid is darker than it should be but not black). As I drive it 40mi home, CEL turned on after 10mi or so. Stopped into Advance and they identified it as P0431. Doing some research on here it looks like it is a bad pre-cat, radiator side. I think it's
the cat and not an 02 sensor because It's louder than I think it should be, and I can smell exhaust in the cabin. I would like to do this fix myself but I've read that a bad precat can lead to engine failure from the EGR sucking up bits of the cat into the cylinders. I am by no means a mechanic, but I'd like to know how I can tell if this has already happened. Since i just bought the car, I don't really know if it's down on power, it doesn't seem to be, just going off of feel, but I'd like to do as much preventative maintenance as possible while replacing the cat. Does anyone have any advice or tips for proceeding? I haven't driven it since I got home and parked it that night.

thanks

Welcome to the group.
What @bluedevil6 says is good advice. If you plan on keeping the car for a little bit I would cont on about $1300 USD.
If you have a bad front pre-cat (P0431) it is a good be that the rear one is going too (P0421). The 06-08 had a different exhaust routing which helps to save the motor but if you are using excessive oil it may be too late.
The coils fail which allows a misfire to develop and in turn this kills the cats. If the front (pre-cat) fails it disintegrates and will fill the downstream cat (you have 4 total).
If you are smelling exhaust in the cabin then you likely have at least one broken exhaust manifold stud. This could be a deal breaker for you (or nothing at all). Mine was broken below the surface of the head (firewall side) and I had to drill it out (~20hrs work) but I saved it. Otherwise the worst is rusted bolts to deal with.Many of us have done it and if you do, it may earn you a "saved a 1st gen" badge...when they are made.
Here is my parts list (your numbers will vary)
https://forum.mazda6club.com/members...l#vmessage9866

Another thread of mine
https://forum.mazda6club.com/3-0l-v6...ml#post4809001


Best of luck.


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post #4 of 24 (permalink) Old 02-22-2019, 06:07 PM Thread Starter
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thank you both for the help. I should revise slightly: my (pregnant) wife smells exhaust in the cabin. I can definitely smell it outside but it isn't overpowering or anything in the cabin, at least to me.

My plan is to get it running enough to not kill itself so i can drive 10 miles away and get the Takata recalls done, and then use it lightly. I would replace front cats, atf, oil, 02 sensors, coils + plugs at once. I can handle the two front cats at the same time, but idk if i can afford all 4 at once. When should the two rear cats be replaced, if not that day? Obviously this varies and I don't expect a definite answer, but other than ASAP, how much usage do you think would be safe on those rear cats, everything being equal? or is it just worth it to wait and do all 4 at once?

Also, its worth noting that to avoid further damage, I've only driven the car from where i purchased, to back home (about 40mi) so IDK if im burning a ton of oil, if any. I'd hate to replace the cats and have the engine give up due to the damage already cause by the old ones. Do you know of any way I can tell if it's eating oil without risking further damage?

sorry if my questions are ambiguous, trying to wrap my head around my next step.

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post #5 of 24 (permalink) Old 02-22-2019, 06:21 PM
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An alternative to replacing the cats right now would be to gut them. You have an 07 so its easy to do with them on the car with a long drill bit, also since you have a post-facelift 6 IF you can get the y pipe unbolted you would be able to see directly into the other cat under the car. There are only 3 on the post-facelift versions the precats then 1 downstream cat just behind the subframe.
The downsides to gutting them is 1) you will fail emissions tests if you have them 2) you will be polluting more 3) it will probably continue causing a CEL


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post #6 of 24 (permalink) Old 02-22-2019, 06:24 PM
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If the engine was toast it would probably be smoking you would probably have a misfire and it would be running like s**t if its not doing these you should be ok. Basically when it eats cat dust it essentially sands down the cylinder walls and Im sure you can figure out the result lol


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post #7 of 24 (permalink) Old 02-22-2019, 07:01 PM Thread Starter
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Quote:
Originally Posted by bluedevil6 View Post
An alternative to replacing the cats right now would be to gut them. You have an 07 so its easy to do with them on the car with a long drill bit, also since you have a post-facelift 6 IF you can get the y pipe unbolted you would be able to see directly into the other cat under the car. There are only 3 on the post-facelift versions the precats then 1 downstream cat just behind the subframe.
The downsides to gutting them is 1) you will fail emissions tests if you have them 2) you will be polluting more 3) it will probably continue causing a CEL


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@bluedevil6 I apologize, I'm a bit confused as I haven't been under the car yet. @DrFeelGood as well as AllData say I have 4 cats. is this accurate? above it sounded like you said i had three; two pre's and a rear. however my vehicle has dual exhaust, and I'd expect two rears.

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post #8 of 24 (permalink) Old 02-22-2019, 08:02 PM
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New-to-me 07 S V6 CEL P0431

Quote:
Originally Posted by [email protected] View Post
@bluedevil6 I apologize, I'm a bit confused as I haven't been under the car yet. @DrFeelGood as well as AllData say I have 4 cats. is this accurate? above it sounded like you said i had three; two pre's and a rear. however my vehicle has dual exhaust, and I'd expect two rears.

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No need to apologize! The 1st gen 6 is broken into 2 halves, 2003-mid 2005= 1.0 aka pre-facelift and end of 2005-2008 = 1.5 aka post-facelift. Things were randomly changed by Mazda for this one of which was the way the exhaust is routed.
On a 1.0 the exhaust is as follows:
We will start at the front precat/manifold it wraps around the side of the engine the downstream cat for the front bank is located just under the harmonic balancer; from there it continues up OVER the subframe
Now the rear cat has a j-bend that again goes OVER the sub frame and the downstream cat is located behind the frame before the two pipes come together to run around the fuel tank and split again behind the rear axle to give you the dual tips

On the 1.5 the front precat/manifold runs into a single pipe under the oil pan and this pipe has a y in it, and the rear precat/manifold connects to THE SAME PIPE, then this SINGLE pipe runs UNDER the subframe connects to a SINGLE third cat before routing basically the same as above around the fuel tank

I will try to find some pics and post as well


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To Come lowering springs, sway bars, subframe brace, strut tower brace
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post #9 of 24 (permalink) Old 02-22-2019, 08:17 PM
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1.0 diagram


1.5 diagram



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To Come lowering springs, sway bars, subframe brace, strut tower brace
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post #10 of 24 (permalink) Old 02-22-2019, 08:43 PM
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Quote:
Originally Posted by [email protected] View Post
@bluedevil6 I apologize, I'm a bit confused as I haven't been under the car yet. @DrFeelGood as well as AllData say I have 4 cats. is this accurate? above it sounded like you said i had three; two pre's and a rear. however my vehicle has dual exhaust, and I'd expect two rears.

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I got what you are looking for @bluedevil6 as I have gone down this rabbit hole before


Gen 1.0 (03-05) exhaust routing





Gen 1.5 (06-08) exhaust routing


2006 pictures courtesy of @Final Impact


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