Exhaust manifold Cat replacement on a 04 Mazda 6 3.0L - Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum
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post #1 of 12 (permalink) Old 03-08-2017, 10:00 PM Thread Starter
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Exhaust manifold Cat replacement on a 04 Mazda 6 3.0L

Well I am going to attempt the replacement of the front and rear exhaust manifolds this weekend. Some say remove the IM and go in from the top. Others say to drop the two rear engine cradle bolts to drop the cradle an inch or two as well as the alternator to get by the exhaust studs. Any comments from those that have done this prior would be appreciated. "too much knowledge is better than none at all"
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post #2 of 12 (permalink) Old 03-09-2017, 01:51 AM
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@Drfeelgood just this for the second time. He's likely your best source for good info.
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post #3 of 12 (permalink) Old 03-09-2017, 08:14 PM Thread Starter
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After review of what has to be removed as well as pre soaking what needs to be removed I have decided the easiest would be to remove the intake plenum and remove the rear exhaust from the top end, however the front will be removed from underneath
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post #4 of 12 (permalink) Old 03-09-2017, 09:17 PM
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If you could post an update on this that'd be awesome, I may have to do this soon. Good luck!


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post #5 of 12 (permalink) Old 03-09-2017, 10:47 PM
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It's no fun, no matter how you do it.

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post #6 of 12 (permalink) Old 03-09-2017, 11:53 PM
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Howdy, looks like you have a bit of work there. Worth it when it is running strong again. I did indeed just do this again. Actually, if I am to be honest I have done it 4 times. Originally I took everything apart to replace the manifolds, then the gaskets (again) then to replace the manifolds (because I did not replace all 4 cats originally and it killed the new manifolds) and again because I put it all together and forgot to install the ... alternator...yup.
I'm pretty good at it now. i can strip it in an hour. I will love to hear how going from the top works out. It's 38 fasteners from the bottom (plus panel rivets and O2 sensors)

My Most recent replacement http://forum.mazda6club.com/3-0l-v6/...s-power-3.html

Steps from the bottom http://forum.mazda6club.com/1st-gen/...ml#post4821425

Have fun and let us know how it goes if you get the chance.


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Last edited by DrFeelGood; 03-09-2017 at 11:55 PM.
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post #7 of 12 (permalink) Old 03-13-2017, 12:53 AM Thread Starter
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Thanks guys.Just finished. As I thought bank 1 would remove from the top. I was wrong. Before you start this job make sure you buy the exhaust bolts all the back to the muffler section cause believe me there will be no way of proper removal without removing all the back to the collector. Some manifold studs came out with the bolts but most stayed. I removed the intake plenum on the top of the engine for easier access of the manifold bolts. The EGR tube could not be removed until the manifold was out. Take lots of pictures to make sure which intake plenum vacuum hose goes where. The alternator must be removed from the engine and laid in the compartment as low as possible. In order to do that the right wheel must come off to take out the lower and upper alternator bolts. The bolt on the rear of the alternator can be removed from the top of the engine. The alternator electrical plug did not want to come out easily. I had to pry it out from the rear of the alternator once it was dropped down. The electrical harness that sits along the rear of the engine is held on by two 8mm nuts it can be moved out of the way once the alternator connectors and o2 sensors wires are disconnected from bank 1. I left the EGR and tube off until bank 1 manifold was bolted to the engine. Bank 2 was relative easier. No tricks I could offer on this one. Maybe one is remove and reinstall the upstream o2 sensor before installing the manifold. Dial all studs back into the head without the nuts this is to ensure no cross threading or pulling out the threads of the aluminum head if you happen to interchange manifold studs with those nuts that didn't come off. I would suggest new studs and nuts. I dialed the nuts on with a 1/4 inch ratchet until they were tight then moved to a 3/8 inch ratchet and gave them a quarter turn. Remember aluminum is soft and you could easily pull those threads. Spray everything you will be removing a day or two previous to repair with penitrating fluid. I used Deep Creep. Make sure to use a little antiseeze when going back together. Give yourself plenty of time, like two days, keep calm and handle each hurtle as a job in itself. It is a BIG job and I have to I had to use my cut off wheel for those bolts that there was no coming back from. I think the only bolts that I could actually used my impact on were the 19mm holding the collector flange to the rear muffler section. Other than that there was no room for it. Well good luck a little patience and a lot of beer
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post #8 of 12 (permalink) Old 03-13-2017, 01:02 AM Thread Starter
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Dr Feelgood It seemed to me like you could pretty much gain all access to the alternator with the right wheel removed. Wow! Everything removed in 1 hour. That is amazing. I could of used you here this past weekend. If this makes any sense I wish I would have completed this job at least once before attempting
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post #9 of 12 (permalink) Old 03-13-2017, 02:34 AM
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Quote:
Originally Posted by mbierbac View Post
Dr Feelgood It seemed to me like you could pretty much gain all access to the alternator with the right wheel removed. Wow! Everything removed in 1 hour. That is amazing. I could of used you here this past weekend. If this makes any sense I wish I would have completed this job at least once before attempting
So... how was the after? Did you notice a difference? What did you find inside the exhaust pipes?
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post #10 of 12 (permalink) Old 03-14-2017, 06:06 PM Thread Starter
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So... how was the after? Did you notice a difference? What did you find inside the exhaust pipes?
Well Three days after and several cold starts. Still no 0421 codes coming back. All seems to be good. Only NAPA auto parts sold me a flat manifold end gasket instead of the O ring donut style that I need. I just have to replace that and all done. I found the rear manifold to be empty when removed. That explains the code the front was plugged and melted platinum particulate remained. That explained the bank 2 sensor 2 high voltage reading on live data. Oh and my readings for the rear manifold bank 1 down stream had the same readings as the upstream. Also the cause for the plugged bank 2 manifold was found to be from a non operational PCV allowing a great deal of oil to enter into my intake plenum. PCV replacement now fixed that. It's too bad my particulate in that manifold is melted. I know a number sites experiment with trying to bring back a failing cat converter with no luck. I was going to try a process similar to that of electroplating only using a slightly alkaline solution and a battery charger in a bucket with a mild steel rod(insulated of course. We don't want to do anything dangerous)

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