Aston177

Hi everyone. I have a 2007 automatic RX-8 and I ran into something weird tonight. Before I get into this, I have to mention that my plugs need to be replaced. I took them out and cleaned them so I can use them until my new plugs arrive. I ordered new plugs, wires and coils. I also have a check engine light. Code - P0138. My mechanic said it'll go away once I replace my plugs.

A few days back, I noticed that the transmission tunnel trim gets quite hot. My car is RHD and after about an hour of driving I feel the heat on my left leg! The carpet right next to the footrest gets pretty warm. I popped the trunk and pretty much everything inside it was hot to the touch. That got me thinking that it could be the exhaust. I checked the exhaust barrel and it was burning. So were the exhaust tips. Almost burnt my finger trying to touch them haha. So pretty much the whole transmission tunnel trim is warm/hot.

I thought my cat was clogged. To verify this, I took my car out for a drive tonight to see if it was glowing. Drove around for about an hour. Pulled up beside the road and checked under the car. Cat was not glowing. I've heard that when the cat is clogged, this car spits flames. Was with a friend so I told him to video the car while I rev it.

The first time I revved, it went up to about 7,000rpm. Didn't go higher than that. The second time I revved it, it went all the way up to 7,800rpm. Heard the shift beep too. So I kept revving it for about 30 seconds. Suddenly my car refused to rev. It kept revving slowly and eventually didn't rev past 3,500rpm. I quickly let go of the throttle but the revs didn't drop. It was stuck at 2,300rpm for about 4 seconds and then slowly went down to 800rpm. Revved it again. Didn't go past 3000rpm. Revved it again after 5 seconds. Went up to 6000rpm. We decided to head back home. I didn't have power loss. Revved it again after about 10 mins and it went up to 7,800rpm.

Could this happen because my cat is clogged?

I have to say that, even though my plugs are old, there are no hesitations when revving. Except this, which happened tonight...

Sorry for being so long. I had to explain what was going on

Help?

CRO8TIA

1. Change mechanic
2 Check the connections on the rear O2 sensor
3 Drop the exhaust and check if your cat is clogged

Aston177

Thank you for the quick reply

Yes I will check the cat as soon as possible. So this is 80% a cat issue, right?

Tweeked86

This definitely sounds like a plugged cat. It runs fine at lower rpm's but just wont rev out right? You can test with a pressure gauge at your #1 o2 sensor bung to measure backpressure.

A misfire will dump excess fuel into your cat and melt it right quick.

Aston177

It used to rev fine. It's just that tonight when I kept revving it to check if it spits flames, it stopped revving after about 30 seconds. It didn't go past 3000 rpm. I was worried that it'll stall because it didn't respond to my accelerator pedal much. But it didn't stall. Got me worried sick!

Btw, is there a rev limiter in auto RX-8s when in Park? Because the first time I tried to rev it, it didn't go past 7000rpm. The second time I tried, it went up to 7,800rpm.

niteshade247

I could be wrong but when you hit the beep you could have hit the fuel cut off I have never hit it but I have in other cars and that sounds about right as for the heat clogged cat got to be or it's about to clog mine was same it would get hot enough to heat the cab of the car but never glowed red as for flames mine now dose it ( put a mid pipe in place of cat) but never did it with a cat. BTW cops don't like flames shooting at them.

RIWWP

iTrader: (2)

A cat that no longer has the internal catalyst elements will enable the engine to spit flames. A clogged cat will not spit flames, because at least one element is still there.... blocking the entire exhaust.

Stop trying to diagnose it with checking for tailpipe flames


And yes, there is a safety mechanism where if the car is stationary and the revs exceed X RPM for Y time, the ECU disables the throttle input and returns the car to idle until the throttle is released. There was a few car fires a ways back on various Mazda models from idiots holding the revs high while not moving, and they implemented this safety across all their cars that use an electronic throttle.

Aston177

Ok so it's pretty much a clogged cat, right? I guess I'll have to gut it out as I'm too broke to get a new one haha. Just a couple of questions.

1. Can I "fix" my stock cat by giving it to an exhaust shop?
2. Will any aftermarket or stock cat for another car which is similar in size work with the RX-8? I'm asking this because these cars put out a lotta heat and they might not be able to take it.
3. Would any aftermarket mid pipe work? Something that's NOT designed specifically for the RX-8?
4. Are there any side effects from gutting my cat?
5. Can I use my gutted cat forever?

RIWWP, so you're saying that my car didn't rev after revving it for 30 seconds because the ECU stopped me from revving it? And not because of my clogged cat?

RIWWP

iTrader: (2)

1: Yes, if you also give them a catalyst element to weld into place. There is a specific metallic core Magnaflow part number that appears to hold up under the RX-8's exhaust heat for about $100, though if you are in CA it will probably not pass emissions there.

2: Your assumption is correct, piston engine cat elements crumble and melt under the RX-8's heat, some as soon as a few miles.

3: any catless midpipe that is designed to fit the RX-8 will "work" for clearing the clog, however a midpipe that is designed for a different car probably won't have the correct geometry (length, bend angles, etc...) to fit between the catback and the header in the correct spot under the car. Here is an underbody shot, where you can see the cat pipe.


4: you will get quite a bit more in the way of fumes and odor, though this can be tuned out quite a bit if you get a Cobb AccessPORT or MazdaEdit. You will no longer have as much heat building up pre-cat next to the engine, your engine will make more power, you will be spitting flames or backfires under the right conditions (easily reached), you will not pass a sniffer inspection, you will probably get P0420 CEL unless it's masked by an AccessPORT or MazdaEdit reflash. Going catless is the preferred choice for quite a few of us.

5: Yes, under the above conditions, until the metal itself rusts through.

6: Yes, that is what I'm saying. I don' think the later rev limit problems are connected to that, however I have never experimented with that ECU feature on an automatic. It could have differing ways to lift the restriction than the manual. The manual it lifts the throttle cut as soon as you take your foot off, and you get the full 9k redline immediately back. The automatic may be different, however I doubt it.

Aston177

RIWWP, that's a lot of valuable info. THANK YOU. And thanks for the picture. Been looking for a proper pic of the car's underbody for ages.

Going in relation to my questions and your answers.

1. Have people done that? Is it successful?

2. So an aftermarket cat won't work?

3. What if I make one? Or get one that's just right and weld it in place? I'm sure there are tons of midpipes that ricers fit into their civics haha. Wouldn't be so hard to find one that fits. My main concern is the heat. Will it be able withstand the heat our cars put out?

4. So, almost all of them are plus points :D Except for the fumes, sniffer test issues and the CEL. I don't mind those. And I really don't wanna get an AccessPORT or MazdaEdit. I have no experience with them and I don't wanna mess something up and screw up my car haha. I'll live with the CEL.

Yes I've heard that gutting a cat increases the cars power. Will my car have more power compared to the power I have now (with my clogged cat) or compared to a car with a good cat?

5. And that's gonna last for like what? 10 years? Seems pretty good to me :D

Thanks for everything. I guess you're right about not being able to rev. I don't know jack about this car. I baby it so much. And I love it to death.

I gotta say, without this forum, I'll be dead. Seriously, this is one of the most helpful forums out there. I might be a new member but I've been reading threads for over 3 years now. I've learned so much

RIWWP

iTrader: (2)

1: Yes. Contact HiFlight999 for the specific part number he is using. He has been using it for a few years I believe, without a failure. I don't know what emissions regulations he needs to pass (if any), and what mitigation methods he might have used to pass them

2: See #1

3: A midpipe is basically just a metal shell. If it fits, it works. There are quite a few already specifically designed for the RX-8, and cheap enough that making your own will probably cost more than the cheapest of the midpipes. The absolute BEST midpipe out there (in my opinion) costs $500, and is provided by BHR. The problem with most midpipes is that they don't muffle the rotary rasp much, if at all. The less you pay for your midpipe, the more rasp and drone you will have to deal with, and it gets REALLY annoying. Midpipes that use some sort of packing to muffle the annoyance WILL fail, and they will fail fast. Same reasons that most aftermarket cats fail fast, our exhaust heat is considerable. Even the BHR pipe was designed with a heavier duty resonator because the original ones were having failed welds under the heat. Only the Racing Beat and BHR are resonated, and the Racing Beat one uses 2 resonators and they aren't all that successful at negating rasp and drone. The BHR midpipe is the only one developed so far that kills all rasp and all drone, and there isn't anything to fail. I used one for 55,000 miles year round in New England before I sold my 8, and it was still as perfect as the day I installed it. Plenty of people buy a cheap midpipe to start, then find out why people always get rid of them, and end up spending $600-$900 in the long run once they end up just getting a BHR pipe. Smarter people just start with BHR and pay less

4: Going catless from having a functioning cat will gain around 10whp. It's one of the only sure power increases available for the RX-8. A clogged cat can kill as much as 120-140whp, so yeah, a huge gain over that.

5: depends on the metal and the driving environment

Aston177

Once again thank you for the information.

So a midpipe not made for an RX-8 ain't gonna cut it, right? If I'm getting one, I should get a BHR midpipe. Thanks. $500 is quite a bit, but I'll see what I can do.

About the rasp, gutting my cat won't make the exhaust too raspy, right? I've seen a lot of YouTube videos of gutted cats and, although they're slightly raspy, they're not annoyingly raspy. I really don't want a loud car with an ugly exhaust note

You said going catless increases power. Does having a gutted cat mean I'm catless? And if that's the case, gutting my cat will give me 10whp? One more question sir. Does gutted cat = midpipe?

Thank you so much

RIWWP

iTrader: (2)

Look at the picture above again. You have to have a midpipe or cat that is exactly the same length, have the same bends in the same angles, and have the same mounting flanges at either end. If the length is off half an inch, you either can't get it to fit between or it will never seal and you will have an exhaust leak. If a bend is off a couple degrees, the flange at one end will be out of place and in order to get the bolts lined up the pipe will be pushing against something, or it may never line up at all. If the flanges don't have exactly the same bolt pattern in the same orientation and number, you won't be able to bolt it at all.


No, a gutted cat will still be plenty raspy. And yes it will be annoying after a while. Feel free to experiment and see what i mean.

Yes, catless = no cat element cleaning the exhaust. Whether that is a midpipe or a gutted cat. A midpipe can have a cat element installed, and the term "midpipe" is technically just another name for the pipe that holds the OE cat. However we typically call a catless aftermarket pipe a "midpipe", the OE pipe with a cat a "cat", and any other combination by whatever the hell someone wants to call it

Aston177

Thank you so much. I'll gut my cat and see what it's like. After all, it's free :D

I'm getting a foul smell from the exhaust as well. I guess that's a combination of my clogged cat and bad plugs/coils.

RIWWP

iTrader: (2)

I'd inspect it before gutting it to be sure. If it's dead, it's dead. But if it isn't dead, then it is generally ill-advised to destroy a $1,300 part that still has value

Aston177

But all the symptoms lead to a clogged cat right?

High heat. Foul smell. Driving the car with old plugs and coils etc...

RIWWP

iTrader: (2)

Yup, agreed, the symptoms do point that way. Just do your due diligence to validate before taking blunt force objects to expensive parts

Aston177

Thank you sir. Will do thanks to everyone who helped me out. I'll report back after gutting my cat

Aston177

I sent you a PM RIWWP

Aston177

Hi guys. I just gutted my cat an hour ago

We first took it out and examined it. Taking it out was a missive pain. Those nuts just didn't come off. I think the extreme heat had something to do with it. Eventually we took it out. The first part looked intact. But we didn't know how good the second part was. My mechanic poured water into it and only a few drops came out the other side. It was clearly clogged. He told me that he can clean the carbon with oil, kerosine and pressured water, but I just told him to gut it. The top part (or grill. I don't know what you call it :P) was pretty easy to break. The second one was quite hard. But eventually we broke it, cleaned it completely, washed it with water and put it back on.

On first start there was a lot of white smoke coming out of the exhaust. The fumes were extremely rough. Made me choke haha. But at least it didn't smell like rotten eggs. A lot of smoke came out when I revved it but after about 10 mins it completely stopped.

To be really honest, I didn't notice a power increase. But maybe it's coz I've only had this car for a few weeks and even with the clogged cat, I never got the chance to properly floor it. It does sound slightly louder and deeper. I like it. After all it only cost me $30 :D

I'll try to do what I did earlier (check for flames hopefully I'll get some now) and see if the engine still refuses to rev after 30 secs of revving and report back.

Thanks so much for all the help everyone

Aston177

Here are some pics of how the inside of the cat looked and the debris.

niteshade247

After pulling that out of the cat go get a compression test with a clog that bad it could have done damige to the seals on the rotors. Normal piston engine just might have thrown a rod with that kind of back presure.

Aston177

Hi. Yeah I should get a compression test done Does the inside look bad to you? I thought the first part (the one shown in the pic) looks pretty intact.

I have more updates the center console still heats up :/. So does the foot rest. I'm guessing this is normal? :/

I drove the car for around an hour today and after I got home I thought of just checking the engine out. Guess what? It was BURNING HOT! I touched the stabilizer bar that runs across the engine bay and almost burnt my hand! Even the hood was pretty uncomfortable to touch. Is this normal? I know rotaries run hot, but THIS HOT?

I must say that it was around 92 degrees outside, so pretty hot. I also noticed that there were air bubbles inside the engine coolant tank. Again, is this normal? I searched around but couldn't find a proper answer. The coolant level was way over the Full mark as well.

Aston177

This is what I'm talking about. It's way over the full mark and it's got air bubbles.

RIWWP

iTrader: (2)

Yes, the tank is an expansion tank, it will develop bubbles. Your ambient temp is 92 degrees? If so, then yes, your engine bay components will tend to hover in the 190F-230F range, if I recall my IR thermometer tests correctly.