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post #281 of 393 (permalink) Old 08-19-2013, 11:50 AM
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I have an 2003 at 129,100 mi. Had some somewhat major stuff be replace, but most of it was proactive/necessary for any car in general with mine hitting the big 1-0 this year.

Two concerns and maybe someone can speak to these two things: pre-cat failure and the JATCO transmission. I have the original transmission on here and done one drain/refill with the correct fluid even if it cost me a premium. The tranny seems to be functioning alright. Did have a spell where it was jumping when changing to 3rd for a couple of days, but it randomly stopped. My other concern is the pre-cats. Given my milage, should I be preparing for those to fail soon?
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post #282 of 393 (permalink) Old 08-19-2013, 09:17 PM
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125,xxx on my 06 mazda6s runs like a champ!
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post #283 of 393 (permalink) Old 08-20-2013, 06:18 PM
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Originally Posted by jm03 View Post
I have an 2003 at 129,100 mi. Had some somewhat major stuff be replace, but most of it was proactive/necessary for any car in general with mine hitting the big 1-0 this year.

Two concerns and maybe someone can speak to these two things: pre-cat failure and the JATCO transmission. I have the original transmission on here and done one drain/refill with the correct fluid even if it cost me a premium. The tranny seems to be functioning alright. Did have a spell where it was jumping when changing to 3rd for a couple of days, but it randomly stopped. My other concern is the pre-cats. Given my milage, should I be preparing for those to fail soon?
As for Precats, we have yet to find an absolute reason for their failure. Some have failed as early as 50k, others have seen nearly 300k. The rule with catalytic converters is they don't like short trips. Short trips don't allow the to heat up all the way and burn off the Unburnt fuel from a cold start.
I have an 80 mile (95% hwy) commute round trip, but I benefit from a carpool, so I just turned 101k. I'm really not worried about it. A set of aftermarket manifolds is available from Amazon for under $500 shipped. If it happens, that's what I'll do.

If you get a CEL, and suspect the cats, unplug the EGR valve, that should help stop the EGR from pulling in the cat fragments and trashing the engine.

If you're worried, do the EGR bypass and call it a day.


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Last edited by joebrez; 08-20-2013 at 06:20 PM.
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post #284 of 393 (permalink) Old 08-21-2013, 12:23 AM
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76,504 miles and still running strong.


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post #285 of 393 (permalink) Old 08-30-2013, 10:33 PM
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Quote:
Originally Posted by joebrez View Post
As for Precats, we have yet to find an absolute reason for their failure. Some have failed as early as 50k, others have seen nearly 300k. The rule with catalytic converters is they don't like short trips. Short trips don't allow the to heat up all the way and burn off the Unburnt fuel from a cold start.
I have an 80 mile (95% hwy) commute round trip, but I benefit from a carpool, so I just turned 101k. I'm really not worried about it. A set of aftermarket manifolds is available from Amazon for under $500 shipped. If it happens, that's what I'll do.

If you get a CEL, and suspect the cats, unplug the EGR valve, that should help stop the EGR from pulling in the cat fragments and trashing the engine.

If you're worried, do the EGR bypass and call it a day.


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The original pre-cat manifolds are way better than anything you get from the aftermarket. Pre-cat failure is a chicken or egg situation. I would like to know if these low mileage engines that had failed pre-cats had other problems as well. Generally if a pre-cat is truly defective, it won't go 50,000.

Also, if a pre-cat does disintegrate, going through the egr system is the long way around. The debris gets into the cylinders during valve overlap when both valves are open simultaneously. Cylinder pressure is low at that point in the cycle and the higher exhaust pressure will drive the chunks in. This happens with piston failure too. The chunks from the failed cylinder will get drawn into the adjoining cylinders.

- Pete
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post #286 of 393 (permalink) Old 09-01-2013, 08:08 PM
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Originally Posted by LBPete View Post
The original pre-cat manifolds are way better than anything you get from the aftermarket. Pre-cat failure is a chicken or egg situation. I would like to know if these low mileage engines that had failed pre-cats had other problems as well. Generally if a pre-cat is truly defective, it won't go 50,000.

Also, if a pre-cat does disintegrate, going through the egr system is the long way around. The debris gets into the cylinders during valve overlap when both valves are open simultaneously. Cylinder pressure is low at that point in the cycle and the higher exhaust pressure will drive the chunks in. This happens with piston failure too. The chunks from the failed cylinder will get drawn into the adjoining cylinders.

- Pete
LMFAO. So exhaust comes back into the combustion chamber during valve overlap? OMG, so the exhaust valve sucks exhaust gases back into the combustion chamber from the exhaust manifold!!! Lol
The 03-05 6's ability to bring the precat material via the EGR has been well documented and is fact.

The precat is in the EXHAUST!!




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post #287 of 393 (permalink) Old 09-01-2013, 10:17 PM
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When you get done laughing, hear me out. Do you know what valve overlap is? The intake valve actually opens towards the end of the exhaust stroke. The exhaust valve doesn't close until the piston is on its way back down in the intake stroke.

Now when you have a precat failing, it restricts the exhaust flow causing more exhaust pressure then normal. The intake valve is open so you have manifold vacuum there and the exhaust pressure is high, so which way will the flow go? It will go from the higher pressure in the exhaust manifold towards the lower pressure combination of manifold vacuum and the low pressure caused by the expanding volume of cylinder when the piston descends.

I've seen newly installed replacement engines ruined by debris from the previous engine failure left in the exhaust manifold. Big chunky stuff can get drawn back into the engine this way.

I'm also not saying it can't go through the egr system but it's the less likely route.

- Pete
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post #288 of 393 (permalink) Old 09-02-2013, 01:15 AM
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When it comes to the 6, they don't clog, they break apart. You won't have reduced back pressure, where valve overlap is even in the equation.

The EGR system had put quite a few 6s in the junk yard... Hence the redesign in 06.

I was an ASE engine rebuilder...


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post #289 of 393 (permalink) Old 09-02-2013, 01:24 AM
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Pete. Take a look at the clustered mess Mazda calls an exhaust on the 03-05 V6 models.

You'll get it then...

(hint) EGR Is after the precat, making it very easy for the EGR to pull in Precat "dust" and deposit it right into the intake manifold.
In 06, the EGR was moved to before the precat.


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post #290 of 393 (permalink) Old 09-02-2013, 07:50 PM
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bought mine in feb. of this year at 116k. now at almost 123k. 2003, and no major issues!
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