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post #1 of 19 (permalink) Old 12-19-2017, 12:23 AM Thread Starter
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Not really new, but haven't been here in awhile

It has been awhile since I monitored this forum, so I had to re-register a new account. I have a 2003 Mazda 6S. I joined in 2003 before I bought my 6. I remember reading about the failing cats when they started failing in around 2010. I recall at the time that they were starting to fail at about 140K miles. I now have 130K miles on my 6, so I came back to research any recent developments. I have been looking on 6crew too. However, I can't see many of the photos on 6crew and can't get to much here.

I'll keep looking, but at the moment the EGR mod is hidden without pics or access. Perhaps I should replace the cats and O2 sensors before they fail.

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post #2 of 19 (permalink) Old 12-19-2017, 01:07 AM
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Welcome back. There is a lot of info on here about the cats including some recent work done by @DrFeelGood on is v6 wagon. He's got a thread on here about how he started with just the pre cats and then ended up doing all of them (including the pre cats again). I'm sure he'll get on here and link you to the thread.

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post #3 of 19 (permalink) Old 12-19-2017, 08:04 AM
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Welcome back to the forum!

Send me a PM if you'd like and I can try to get your old account back in action. As for this account's inability to view/post things, the forum owners did this a while ago to help combat the crazy amount of spam bots we had on the site. You should be good within 24 hours (now that you've posted for the first time).

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post #4 of 19 (permalink) Old 12-19-2017, 04:30 PM
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Quote:
Originally Posted by estel View Post
It has been awhile since I monitored this forum, so I had to re-register a new account. I have a 2003 Mazda 6S. I joined in 2003 before I bought my 6. I remember reading about the failing cats when they started failing in around 2010. I recall at the time that they were starting to fail at about 140K miles. I now have 130K miles on my 6, so I came back to research any recent developments. I have been looking on 6crew too. However, I can't see many of the photos on 6crew and can't get to much here.

I'll keep looking, but at the moment the EGR mod is hidden without pics or access. Perhaps I should replace the cats and O2 sensors before they fail.
Hello, welcome back...again.

Catalyst talk eh... Well the cats should never fail. They are killed. I think the problem with the early mark 1 series 1 Mazda6 (03-05) is the tendency to develop a misfire. This is exacerbated by a fairly convoluted exhaust plumbing that was corrected in the series 2 and further remedied in the Mk. 1 Fusion. My personal experience is a misfire from a previous owner putting Autolite copper spark plugs in place of the Motorcraft Platinum plugs the car came with originally. With the un-burnt fuel going into the catalyst, it cause a sustained overheat (sulfur smell) that resulted in melting and disintegrating. Other owners report COPs failing and I have hears of faulty injector wiring also contributing.

If you do not have a misfire (and never have) I would replace the O2 sensors (4 of them with a lifespan of 100,000mi) Plugs and coil packs. Also consider doing the EGR mod ( I have not but am looking into it)


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post #5 of 19 (permalink) Old 12-19-2017, 05:25 PM Thread Starter
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Quote:
Originally Posted by DrFeelGood View Post
If you do not have a misfire (and never have) I would replace the O2 sensors (4 of them with a lifespan of 100,000mi) Plugs and coil packs. Also consider doing the EGR mod ( I have not but am looking into it)
Thanks for the update. That is helpful. My '03 6S has had occasional misfires. I have had to clear a CEL (or MIL) code about every 3 years for a cylinder 4 misfire. I replaced plugs at about 60K the first time just because it was due. It developed a persistent misfire at around 115K. I drove it maybe 300 miles before replacing plugs and coil packs. That fixed the misfire, but I am concerned that some damage was done to the cats.

I will definitely replace the O2 sensors soon as you suggest. Plugs and coil packs only have 15K miles on them now so they are fine. I will look into the EGR mod if I can access the description with photos. I tried to read the description on 6crew but it doesn't make much sense without the photos. Is it available on this site?
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post #6 of 19 (permalink) Old 12-19-2017, 07:56 PM
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Quote:
Originally Posted by estel View Post
Thanks for the update. That is helpful. My '03 6S has had occasional misfires. I have had to clear a CEL (or MIL) code about every 3 years for a cylinder 4 misfire. I replaced plugs at about 60K the first time just because it was due. It developed a persistent misfire at around 115K. I drove it maybe 300 miles before replacing plugs and coil packs. That fixed the misfire, but I am concerned that some damage was done to the cats.

I will definitely replace the O2 sensors soon as you suggest. Plugs and coil packs only have 15K miles on them now so they are fine. I will look into the EGR mod if I can access the description with photos. I tried to read the description on 6crew but it doesn't make much sense without the photos. Is it available on this site?
If your car does not smell like sulfur when you drive normally and you do not have P0421/P0431 codes I would imagine you are okay. The codes mean the (upstream) "pre-cat" is not working. The sulfur smell means the engine is working harder to expel gasses (at least mine was) and working too hard. I would smell rotten eggs every time I pulled to a light or stop when the air was still towards the end of the last catalysts.

I am linking a pic from @98se5speed and his take on the modification.
.
Notice the filter down on the EGR tube, this is to keep the intake from sucking any debris in.
Others run a tube to the filtered portion of the air box and connect it with a nipple (as far from the MAF as possible)
The other side of the tube where it attaches to the exhaust is covered.
Back in the day on the 6crew page @flipper (I believe) listed this part ford 0-w705609-s430
as a replacement to cover the EGR nut in place of the one with a hole for the tube. I have not verified fit on this.
I will likely try it when I find an air box lid at the salvage yard I can play with.

Hope this helps a bit


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post #7 of 19 (permalink) Old 12-20-2017, 02:07 AM Thread Starter
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I went ahead and ordered all four O2 sensors and that plug. Thanks for the part number.

I don't get a sulfur smell nor those codes. The only codes I get are the cylinder 4 misfires, about once every 3 years. The only smell I get is from oil burning on the exhaust pipe. I think the oil is leaking from the timing cover, because I have replaced the front crank seal and the oil pan gasket.

Thanks for the photo of the EGR mod, I can't see what that filter connects to but it must be the bottom side of the EGR valve. Is that right? I conclude that the plug is used on the exhaust to block off the tube to the EGR valve. Right? Does the new hose from the air box go to the EGR valve where the tube now connects (facing towards the exhaust)? How are people connecting the hose to the EGR valve?

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post #8 of 19 (permalink) Old 12-20-2017, 12:58 PM
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Quote:
Originally Posted by DrFeelGood
I am linking a pic from 98se5speed and his take on the modification.

Notice the filter down on the EGR tube, this is to keep the intake from sucking any debris in.
I ran that setup for quite some time, never had any CELs from it. But I don't think my setup or running a hose to the intake is a great solution.

I've been fighting with my car seeming "rich and sluggish" probably since I got it on the road. Worst part is that it's not ALL the time, but often enough that I've tried many many things to fix it. Sure, these engines aren't powerhouses at low RPMs, but mine often seems excessively bogged-down and the exhaust smell is often very rich or smells of raw gasoline.

My setup: 2004 with an 09 Fusion V6, 09 Fusion fuel rail & lower intake, Injen CAI, 3.7 TB + spacer, MSDS headers, downstream O2 sensors in spacers to avoid CELs for no precats.

Things I've replaced on my quest to running cleaner & meaner:

- Ignition coils: OEM Ford coils from 2009 Fusion engine
- Spark plugs: OEM Motorcraft Platinums
- Fuel injectors: Brand new OEM Ford units for 04 Mazda 6 (different part # than Fusion injectors)
- Upstream O2 sensors: Brand new NTK (OEM mfg) Fusion V6 sensors, adapted to Mazda 6 connectors

And overall... my car is still relatively bogged and rich most days.

Getting back to the EGR topic, I kept having a noticeable throttle surge at times. I thought maaaybe something was a little goofy with me running the 3.7 TB so I ignored it for a while. But then I started researching "engine runs rich" and some people spoke of leaky EGRs letting in air that hasn't gone through the MAF, throwing things off.

So I put a monitor on my dash tablet that lit up every time the EGR opened. Wasn't long until I saw that my "throttle surge" happened exactly when the EGR opened up. It was essentially an electronically controlled vacuum leak. Mine was sucking in filtered air from under the hood, if you run a hose to the intake you'll probably suck in less (since there's some vacuum in there) but it would still be adding air to the intake that wasn't metered by the MAF.

Upon reading that, I removed my "filter" (piece of a T-shirt with a zip tie around it) from the EGR inlet and plugged it up to allow zero flow. Of course I now have a P0401 code, but the throttle surge went away. And while I thought I had also solved the bogged/rich situation, it came back not too long after. My car pretty much runs "lean and clean" upon an ECU reset, but once things settle in it goes back to running rich. So that's fun.

About the only thing left for me to do is to work on eliminating some minor exhaust leaks. I definitely get a bit of exhaust smell when I run the HVAC while stopped. Having exhaust around the O2 sensors will skew their readings (they're trying to compare the exhaust to outside air) so perhaps sealing up some minor leaks will get more accurate readings for me.

I also have never changed the downstream O2 sensors, but I'm 99.9% sure that they have no bearing on fuel trim, they are only there to monitor precats for emissions purposes. I thought about taking out the spacers just for shits (knowing I'd get CELs for it), which I might do if I ever get real bored.

Alright, long story/rant/contribution done. On a good note, it was 44 degrees here in MI yesterday so I got a chance to get all the salt off my baby. Win.


James - Ann Arbor, MI
2004 6 wagon (3 pedals ftw)
2004 MPV ES (family transport perfection)

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post #9 of 19 (permalink) Old 12-28-2017, 10:02 PM Thread Starter
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Quote:
Originally Posted by 98se5speed View Post
I ran that setup for quite some time, never had any CELs from it. But I don't think my setup or running a hose to the intake is a great solution.
Thanks for sharing your experience with the EGR mod. I appreciate the real-life long-term results.

My preference for now is to replace all the cats before they fail and cause engine damage. All four can be purchased at Rockauto.com for a little less than $1000. Is there a way to tell that the pre-cats need to be replaced before they cause engine damage?

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post #10 of 19 (permalink) Old 12-28-2017, 10:11 PM Thread Starter
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Quote:
Originally Posted by DrFeelGood View Post
If your car does not smell like sulfur when you drive normally and you do not have P0421/P0431 codes I would imagine you are okay. The codes mean the (upstream) "pre-cat" is not working.
I replaced all four oxygen sensors with new NTK parts. Apparently my pre-cats are okay. The upstream oxygen sensors toggle high and low every few seconds, whereas the downstream sensors remain fixed. I forget whether the downstream sensors are high or low, but they remain steady for at least one minute without changing.

Is there a way to know when the pre-cats need to be replaced before they cause any damage to the engine? If you get the P0421/P0431 codes, is it already too late?

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