Clogged Cat 8
 

I have a 2004 M/T 8 with a little over 120k miles on it. Tuesday the check engine light came on and I figured it was just a leaky gas cap. As it turns out, it was for a clogged cat. How long will the car drive with the cat clogged? I've put a little less than 400 miles on the car with the light on. I am in college so I don't really have the money to put a new cat in at the moment. I get out for Winter Break in a week, the 14th is my last day. I will have to drive the car home with the cat clogged, about 160 miles plus another 120-ish miles for work this next week. My only question is, will the car be able to make it for a week and a half with the cat like this? I know that it needs to be fixed ASAP but a week is the best I can do. The car will stay parked unless I have to go to work. What would you guys recommend? Thanks for your help!

I would NOT drive the car with a clogged cat. Since it will need to be replaced anyway, remove the catalytic converter, gut it out, and reinstall. Yes the car will be louder, and smell more, and a check engine light will remain on since there is no cat, but it won't cause engine damage. Just do NOT operate the car with a clogged cat! In severe cases the over heating on the clogged cat and extreme heating of the engine can set the car on fire. Not common, but it has happened.

Alright, I know I shouldn't drive the car at all but I don't have a choice. It is my only car and seeing as how I live 2 hours from all my family, I have to take it to work. One of my friends offered to drive down to help me Monday but I have work today and Sunday. It is about 50 miles for both days, do you think the car could make it then?

If you cannot do the "gutting" yourself, try to find time and have a shop do it for you. It's better to spend a $100 than $5,000 to replace your blown engine because you drove the car with a clogged CAT. After one of your drive from work, take it in a dark parking lot and check under your car. Look for your O2 sensor and see if there is a red glowing ring around it. The red ring is one of the indication that your CAT is bad/clogged, take action. If not, then you are in borrowed-time. Worst case scenario; if you really must and I know everyone here will not recommend prolonging the problem, you can drive it on your trip home but do not try to put too much load on the engine. Stay at a lower RPM.

This is what I experienced when my CAT went bad last year(11/14/2014), I did not even have the P0420 but instead I was having a P0301 trouble code. The car felt hesitant and the CEL will flash everytime I get close to 5,500 RPM. My car had the symptoms for three weeks until I finally replaced the whole ignition system(which is what you should do right away because a weak and old ignition system will certainly cause the CAT to go bad).

I remember that I have driven it for at least a month after putting in new coils, plug wires, and spark plugs; while driving on the freeway for 15 miles the engine is still pretty slow reaching the redline. One of the time I redlined it the engine response felt better on the foot like it had freed up "SOMETHING". Then I remembered the glowing-red-ring-of-death. So, before going home, I drove it in a dark parking lot and looked under the driverside and there it was... The glowing red ring around the O2 center. The next morning I dropped the CAT and the front packing material had broken in peices; I did not even hear the marbles-in-a-can, as some have discribed it, when the packing came loose inside the CAT. The O2 sensor still didn't pick up anything for the P0420 CEL until I removed the peices and gutted it. I now have a gutted CAT and the CEL light sometimes turns off but the P0420 trouble code is still there.

https://scontent-lax3-1.xx.fbcdn.net...c7&oe=56EF9EB3

Good news, I have a friend from back home driving down to help me in the morning. We're just going to straight gut it. I did have to drive it to work today but I didn't notice any issues. I used the torque app on my phone (something I would highly recommend to EVERYONE) and kept an eye on the Cat 1 Bank 1 temperature sensor. It stayed where it usually is, around 1,800F and it didn't increase so maybe the cat is not clogged too bad and I caught it just in the nick of time. I'll post pics and updates in the morning once we finish the gutting.

So wait, how do you know it's clogged? There isn't a code for that exactly.

Well, it's throwing a P0420 fault code which usually indicates "Catalyst System Efficiency Below Threshold" which means that exhaust isn't flowing through the cat efficiently as it should be which would indicate a clog in the cat, correct?

Mine had that code when it went bad along with loss of power at higher RPM.
*EDIT* Be sure it's bad before gutting it. If the front half isn't broken up or melted, shine a light through it.
Also, if the back half is broken up, some pieces can get stuck in the pipe or muffler.
Be sure to take your oxygen sensor out before gutting it so you don't damage it.

I'll make sure to have a good look tomorrow when we're taking the cat apart. I'll update with pics and maybe a video in the morning.

Save those 'moon rocks' for scraps, sell them at a metal recycling center.

I've done some reading about cat temps. It seems like the normal is 1200-1600F for a healthy cat. You seem to be getting 1800F. Isn't that too high? I'm sure someone more experienced than me can shed some light here.

It is, that is why he is going the gutting-route.

Sorry to be gone, finals week. I still havent got the cat off. Those dang bolts are stuck on there, don't worry though, the car has been parked. Also, on the subject of cat temp, I have constantly got about 1600F-1800F since I got the car almost a year ago but it has just now started to throw the code. It not always that hot, usually only when I thrash it around it when it get that high. Does anybody have any recommendations on how to get them off? I know they are 14mm but they are stuck as all get out. They're soaking in penetrating oil tonight and hopefully they'll be good by morning. Fingers crossed!!

You are talking about the rear flange, right?
The nuts on the back side with the springs come off.
The 'bolts' are pressed in studs.
PB Blaster is probably the best penetrant, WD-40 is borderline useless.

https://cimg9.ibsrv.net/gimg/www.rx8...c002b35a25.jpg

So, while we're on the subject, is 1600 to 1800F really too high?

Update: Still nothing haha. I ended up taking the car right down the street to a muffler shop. The mechanic was nice enough to break the nuts loose for us. He had to cut the bottom front one off with a torch. We got the car back to my apartment and still nothing. We did use some sort of penetrating oil, not sure on the brand though. I texted my dad so we'll have to go from there. He said a new cat would be my Christmas present but I'm not sure if I want a new one, I really like the way the car sounds catless.

The OEM one is the longest lasting.
They run around $1400.
Cheaper aftermarket ones don't last.
Good for temporary use to pass emissions tests, and that's about it.
You also have to be sure your ignition system is healthy, misfires kill cats quickly.

I replaced the wires and plugs back in March but never got around to doing the coils so that's definitely what killed my cat. I'm planning on putting some new coils in before the month is up, do you think I'll need to do the wires and plugs too since I just did them in March? I'm hoping I don't need to replace the whole system just because of faulty coils.

Your wires should be fine.
You should pull your plugs and check them just to be sure they're not fouled.
If they are, you might be able to clean them gently with a toothbrush and solvent.
Just don't use anything abrasive on them, they can be damaged by rough cleaning.
I and many others use midpipes in place of cats mainly for peace of mind, slightly better power, MPG, and the sound.
I like my BHR midpipe and stock exhaust.

Well, my dad couldn't get the bolts off either. We took it to an exhaust shop and talked to the mechanic. He said the light came on probably because I got some bad gas that had moisture in it and the water got stuck in the cat or there was some ethanol that didn't burn completely. He said the car sounded fine and since it wasn't running rough it's not the cat but I'm not sure. I'd rather gut it for the peace of mind. I'll get after new coils as soon as I can but for now the solid CEL is something I'm just going to have to live with, I guess. Thanks for all your input guys!

If I were you, I wouldn't take RX8 advice from an exhaust shop 'mechanic' unless they are knowledgeable about them.
Btw, I used to be one of those guys.:)

If you do not talk to someone with rotary engine experience, and more specifically, the Renesis rotary, your best bet is to get advice from this forum.

Trust me, I've learned a ton here in 3 years.
I had that same code 4 days after I bought it.
I have a substantial mechanical background with piston cars, and I thought my car was running way too good to have a bad cat, and I continued to drive it until it actually started losing power at higher RPM.
I finally dropped it, inspected it, and it was really bad.
I probably took some life off of my engine by ignoring it, and lucky I didn't totally kill it.

https://cimg2.ibsrv.net/gimg/www.rx8...4a49ca714.jpeg

If you can't get the cat off, you should take it to a shop that will take it completely off for you and inspect it.
They won't gut it or delete it, but you can pay them to take it down, inspect it, and put it back on with new bolts.
Offer them $20-30 cash, no receipt, guys love that.
If it isn't obviously broken up or melted, shine a light through it, if you don't see light coming through, it's clogged.

Okay, I'll call around a few more shops around town. The mechanic seemed to know a little bit about them. He did mention that if it was running smooth and not stuttering it should be okay. He also said that "when the cats go in these cars it'll sound like marbles in a jar" so maybe he did know a little bit of something. He also said that if the cat goes, the car will sound like a "vacuum sucking in air when you accelerate" but I'll get a few more opinions anyway... better safe than sorry.

He knows about catalytic converters, I do too.
You can drive piston engine cars with clogged cats with much less risk than a rotary.
I never heard either of those sounds, and could not confirm it was bad until I took it completely off.
The exhaust is so rigid on an 8, I think you'd have to smack it with a good sized deadblow to make it rattle.
Just call around and explain that you want to take it completely off to inspect it before you drive over there.
If you have to gut it, there is an actual DIY thread here for it.

Sorry for the late response again. I put some octane booster in it and it's been driving just fine. The check engine light did go off for about 5 days but it came back on again after I drove the car back home. Maybe it's just the coils not sending a good spark and not all the fuel burning, I really don't know. There isn't a loss of power anywhere in the rev range, it revs from idle to 9k just fine with no hesitation. However, it does seem to take a few more seconds to start once the car is warm which I'm thinking is the coils if I'm correct.