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Quick question about replacing my Cat

Old 04-22-2013, 01:28 PM
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Quick question about replacing my Cat

My RX8 threw a CEL and come to find out the Cat needs to be replaced. I ordered the Cat and am picking it up on Wednesday and taking it to my buddies garage and am going to swap it out. I have the flanges to replace while I'm at it, and after doing some research it seems like I need to replace my plugs and wires while I'm at it?

Is there anything else I need to consider? The engine only has 750 miles on it, so do I really need to replace plugs and wires when I know for a fact the plugs were replaced just 750 miles (3 weeks) ago? Or is there something I'm just not aware of that I need to consider here?

Just an FYI, I have searched for this, the stuff I found was on another website not here, which is why I'm coming back here to ask. I tried DIY cat DIY cat change, and a couple other things. I just want to make sure before I go replace this, I may as well do whatever I need to do all at once while I have the day off.

Info about the car:
2005 RX8 GT with 85k miles
New starter, engine has about 750 miles on it, according to the Mazda dealer the only issue is cat.
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Old 04-22-2013, 01:32 PM
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I'm struggling to know where to start in answering the ignition question.

Yes, failing plugs could have killed your cat.
No, THESE plugs probably didn't kill your cat, and you probably don't have to replace them.
Yes, the coils on your engine are the same ones that were on there before your engine replacement, and if THEY are failing they could have killed your cat even with good plugs. Same thing with wires.
No, replacing ignition parts are not hand-in-hand with replacing the cat, since it's possible for cats to fail with good ignition, and it's possible for the ignition to fail, start killing the cat, then you replace the ignition, then the cat dies. In this scenario you wouldn't have to re-replace the ignition.
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Old 04-22-2013, 01:50 PM
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Ok, so a quick search says to check for white marks on the coils to see if they are going bad. I'm not sure they replaced that though, all the dealer said was they replaced the engine and starter, and I know that they left 4 old plugs in the trunk so I'm assuming they replaced those.

So I guess I'll take those out while I'm at it and check it. Doesn't seem like that's something that should have been replaced if they replaced the plugs and engine? It almost seems like this might be a case of a bad cat, I'm just wondering if there is anything else that people usually replace while they are at it. (And I'll check those for the white burn marks)

The BHR ignition system has everything to replace that doesn't it? I was hoping to be able to wait a few months before I did that, but I guess if i absolutely have to I can rearrange some things in the budget and replace it in the next couple months, but I know I can't do it right now. Is waiting 2 months going to completely screw up the new cat?

Last edited by Tethlah; 04-22-2013 at 01:56 PM.
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Old 04-22-2013, 01:54 PM
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  1. Your engine's failing compression may have killed the cat
  2. White spots on the coils mean nothing, you found wrong information when you searched. Do a Google search for: site:rx8club.com DIY coil test
  3. The engine core warranty only covers the engine core. They are not obligated to replace ANYTHING else, even if it seems like it would be "part of the engine". If they do replace anything else, they will most likely charge you for it. If you didn't get it in writing, they didn't replace it. If you DID get it in writing, they still might not have actually replaced it.
  4. There is no "commonly replaced" list when replacing a cat, other than perhaps new bolts since the ones in there tend to get rusty. Sometimes the rear O2 needs replacing, but that's dependent on if it actually has a problem.
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Old 04-22-2013, 02:32 PM
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awesome, thank you for the quick answers, I'm reading up on that test and going to give it a shot, if I'm lucky I can hold off getting the BHR system for a couple months so I can install it later.
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Old 04-23-2013, 07:05 AM
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Originally Posted by ohchad11 View Post
Is it true that the oil recommended is not correct and if so what should be used
Please don't turn this into one of those threads, I actually did do some research before asking my question.
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Old 04-23-2013, 07:13 AM
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