ikkake

I bought 04 rx8 3 months ago as my first serious car - Always wanted to have a modded car and I consider this my learning and training experience. Car was already quite well modified and recommended by a common friend who "knows his ****". It's a one previous owner car, and all the modifications were checked to be a high quality and installed properly. Car also had a Mazda service regularly, often before the due date/mileage. Car came in with CEL light permanently on as well as check coolant light.

Modifications list is as follows:

Blisstein pss9 coilovers
Stoptech front bake kit with uprated bake discs front and back.
HKS hi power cat back
Cusco roll bars front and back.
It was also sitting on pretty much brand new set of 4 potenzas (1 mm wear back and 1,5 mm front).

The car visually had a lot of rough spots, but mechanically and modifications were pretty much great. Except the CEL light and Radiator light which as far as I was assured are pretty much common for the car.

The mileage on the car was 68,000 miles but the engine was rebuild at 35,000.

First thing I did was to give it to a full service check out at an independent garage to see how well the car is maintained/does it have serious issues with it. It was ran though the computer, Oil filter and oil exchanged, Air filer checked and was clean, all the brake pads checked and, well pretty much full service. Computer returned that the CEL is due to bad o2 sensor.

Car was (and is) running amazingly well, has pretty much no problems starting up cold or hot, except nowadays when it close to zero degrees it needs around 1 maybe 2 seconds longer to start up.

Few weeks after I got the car I experienced a power loss as well as weird popping sound when revving down but the idle held well, it started up hot and cold no problem, so I assumed it might be a coil, grounded the car and ordered BHR ignition kit. Strangely enough the problem has not occurred again, car drove to the garage with no issues and computer has not returned a problem with any of the coils. Then again when I swapped the coils to the BHR ones one of the coils was cracked and a bit melted, so I assume it was on it's way out. None of the coils had brown or white discoloration.

After that the car ran amazingly well, I reset the computer memory as well and had no issues again with performance. Except one thing, it really stank from the back as in fume smell. I might have made a mistake of not adressing the CEL then but I was still paying some of the car down and could not afford another upgrade and those sensors are expeeeensiiiiive.

Few days ago I went to the garage for 2,500 oil change ( I made a lot of miles in last few months in this car) as well as trans fluid and diff fluid exchange. I also had a resonant rattle at 2,200 revs I wanted to get checked. The mechanic told me that he removed the heat shield that caused the rattle, it was on the CAT but he said that my CAT is gone - when he banged it the stuff is loose inside. I also got the rotten smell coming out of it but not constantly. Im not sure I had that before as I didn't really know what to look for.

Now the car still performs as it always did, goes fast has nice torques above 5000 revs, red lines with no issues. My mechanic told me that the cat does not obstruct the flow of exhaust fumes so it's basically a decated rx8 now but I read that cat failure can lead to the engine damage. Should I ground the car until I got the replacement? Is it good to drive except I'll just kill few polar bears more and melt some glaciers? I tried to research the topic but I really can't find a lot of specifics except that it will lead to the engine damage, my question is how exactly. Aren't there decated rx8 and they are not only fine but even recommended if not for the legal issues related to it?

Also I'm looking to buy the pettit racing hi flow cat which seems to have a very good reviews, but is it really better to go for BHR midpipe if I can get the MOT passed with it? Wont that mean that the fumes smell will always be there and rotten egg smell as well?

I care of the car greatly, it's always warmed up untill atleast the gauge moves, preferably to full temp. I premix with motul 710, topping up oil pretty much on weekly basis. Oil i use is Fuchs Titan 5W30. I live in UK.

The other symptoms the car has that I'm worried about (although they seem to be considered normal by some) are:

-Car backfires and I mean a lot. And it's not just the popping sound, I often wonder at night did I just got photographed as the flash seems to be quite substantial. I know it's cool as **** and I love it but
a) Isn't car with CAT on pretty much not supposed to backfire?
b) Doesn't that mean that my mixture is fucked and that supposedly killed the CAT?
How do I adress this problem if it even is a problem?

-Car has a problem launching from still, especially uphill, it stalls quite easily and on an incline sometimes it has no power to pull the car up. It is all well after 2-3k revs but I stalled it a lot so far. Issues or just the design feature of the Renesis?

-I still have the CEL light on constantly. Mechanic thinks it's the CAT triggering it. But computer still says those are sensors. I'm pretty sure it's pretty much the same thing so when I'll be buying the replacement shall I buy the sensors as well? What would be the ideal package for this replacement.

I know the car is old, and I know the mileage is quite high but I love this car, and even if it seems to be a money sponge I regret nothing but I really want to keep it running as long as possible.

By the way the car was bought at a Police auction, so there is no way to talk to the previous owner, but the paper log is quite substantial and car seems to be very well maintained mechanically. All the modifications listed are from me inspecting the car and some receipts.

One last question; I was thinking about making a log thread here on the forums showing my adventure with the car from the pretty much a total noob to, well I don't know myself. Would you be interested in a thread like that? With some photos, thought processes and some links a research methods? What I would like to ask in return if you like the idea is for some advice on the each step of this adventure.

Thank you for reading and glad to be a new member of this community.

RIWWP

iTrader: (2)

Newbie posts are rarely this detailed, so thanks for being so complete about it!

Coolant level sensor failure on the coolant light. The sensor fails easily, and is integrated into the coolant bottle. The permanent CEL could be anything, though the cat failure could easily be it.

Yup, sounds like a failed coil. They don't typically melt, but if they have, it's certainly bad.

Cat failure, but at least the "good" failure of a blow out, rather than a clog.

Yup, cat failure. Will cause the CEL and the heavy fumes

A cat WILL obstruct the exhaust flow from the engine. Going to no-cat is a power increase as a result. You will have the fumes of course, but running catless is healthier for the engine than running with a cat. The cat failure that damages the engine is when the cat clogs and becomes a severe exhaust restriction.

The problem with a cat failure leading to engine damage is when the cat clogs up, which isn't what happened to yours. A clogged cat causes the exhaust pressure to build up, saps tons of engine power. Eventually the pressure post-engine is high enough that the engine has severe trouble getting the exhaust out, and the internal stresses start damaging seals. A catless RX-8 reduces the stress on the engine, and a catless rotary can't get engine damage from a later cat clog.

Yes, a catless pipe will always keep the smell around. There are actually some tunes that reduce or even eliminate the smell, but it's going to be pretty bad on the stock tune. High flow cats don't tend to last very long under the rotary heat, but I seriously doubt you could pass MOT without a cat.

You don't have a cat, since the cat element blew out. A catless rotary will pop and flame a lot, and it's entirely normal. When you let off the throttle, there is almost always at least 1 rotor face of the 6 that has received fuel but is now not going to be ignited. That gets dumped into the exhaust, where the fuel gets catalyzed if you have a cat on, but if you don't your hot fuel mixture is going to travel down the exhaust till it finds the 3rd thing fire needs: air. If you install a cat, even a high flow cat, you are going to reduce or eliminate the backfiring and flames.

Not a design feature, but yes, 1.3L engines without much leverage on the crankshaft trying to pull 3,000lbs uphill at low rpm don't generally do it very well. The rotary's peak torque isn't till ~5,500rpm, and it's power band is 4,500+

What are the actual codes? The missing cat code is typically P0420, but it is entirely possible that it will actually throw an O2 sensor failure code instead. Which code or codes you have will depend on what your options are, or even if you need to do anything at all. Get a bluetooth OBD2 adapter, pair it with your smart phone, get the codes and a ton more live data from the engine. No need to rely on the mechanic for that.

You are referring to a build thread. Lots of them exist, and you are certainly free to have one of your own. I even have one on here for a non-RX-8 (https://www.rx8club.com/general-auto...-build-244600/)

ikkake

Thank you very much for the very extensive reply. I actually just came back from the local exhaust specialist and he told me that the cat is not actually an rx8 cat at all, it's some other cat basically welded to the mid pipe. The mesh just started to move and it's not very loose yet but he recommends to get a new cat as soon as possible as the longer it takes the greater chance of the mesh actually rotating and clogging the cat is. I will be decating this rx8 as soon as I got money for BHR midpipe.