I need to know what the car would be doing when or if the cat was clogged or melted on the FD? what would the engine do and would there be smoke from where the DP and cat connect?

 

most likely the engine will sound rough, choking itself, sometimes even start for a few seconds and die right away..
i had that happen to me before, not on the fd.

 

when the one on the GSLSE i had melted the car lost alot of power and when you put your hand over the exhaust there was very little pressure coming out.

 

The first symptom would normally be boost that falls off as rpm increases.

 

I had the front brick in my first hi-flow cat break apart. Idle was normal, as was low boost, but it would not boost past 4psi and was more quit. When I removed it for inspection, and tilted it, all these small pieces fell out.

 

I've had a main cat clog. A clogged cat is like a clog in a drain. Everything seems fine until you try and put more through the pipe than the clog will allow and then it backs up. That means in the case of a main cat clog things seem fine until high RPM when the exhaust flow goes way up.

In my case I was on the track and over the space of a lap or two the secondary boost fell from 11psi to no more than 7psi as I watched. The primary felt fine. Engine ran perfectly fine, turbos still switched over, no smoke no nothing. The only symptom was the secondary boost not building. Upon inspection one of the bricks had disintegrated and the wire mesh which held it in place was clogging the exhaust. All this was visible by peering down the front inlet of the cat with a flashlight.


https://www.rx7club.com/3rd-generation-specific-1993-2002-16/clogged-cat-pics-227840/

 

I guess I meant more at idle what would it do. I saw your thread searching DamonB but, the pics were not attached. I was having trouble passing emissions last week, got to the point where I replaced the stock cat with a new HF cat from Jason over at the 7store. Well, after putting it in, I am getting some really weird symptoms and it all leads to the cat. It is really rough idle, starts up ok, but is running like something is stuck in the exhaust. It is backfiring and also alot of pressure coming out of the tail pipe, also there was an instant plume of smoke from the DP area. I don't have any visable leaks of any kind, plus its instantaneous. Smells like fuel to me. Also after 3 minutes idling, I smelled like I slept in the muffler. Really bad exhaust smell? I noticed that when I give the car a little gas its real choppy and doesn't really rev properly, then starts the backfiring. I also looked down last time I started the car up, and after 2 mins of idling maybe, the cat is cherry red. I have the air pump hooked and the cat is brand new, I drove 20 miles on it and failed an emissions test, went back and changed all I could back to stock and this is what it does. I am wondering if the cat is the problem and how I would know. It was running awesome before I decided to change cats?

 

Did you reconnect the exhaust ground when you swapped cats?

 

That was the same thing mine did only mine was blowing the air pipe off the cat.

 

My car is doing something like that right now. The idle is perfectly fine, and when I rev the car it is fine also...but where i notice it is funny is when I rev it to just say 4000 rpm....it's when the RPM's are coming back down to idle that the car is choppy and i can hear rattling coming from the mid-section of the car, and occasionally some backfires ???????

Anyone any ideas on this or experienced it also ??

 

Thanx guys. My idle is really rough like a V-8. I tried to drive around the parking lot but it was not responding well. I put it back in the garage because I don't want to cause damage, since then I have started her up to the description above. Obviouly something is wrong and why is the cat cherry red after les than 2 minutes at idle cold? WTF? I think I might go back to the stock cat and see what happens. BTW, I did reconnect the ground on the cat?

 

TTT