SS6ixSpeed

Please read because too many things happened to sum it up in a few short sentances.
It's a 96 trans am with 68,000 miles. M6 and stock besides a cat-back.
A few days ago my passenger side cat started rattling. Today, I leave work and it's rattling a little louder than usual so I get into 3rd gear and floor it up to about 4000 rpms to see if it'll quiet down a little before coming to a stop light but right at about 4000 rpms, it cuts power and starts coughing. No, it isn't the pump, I just had it replaced 2000 miles ago.
I get to the light and it idles fine, I get on the interstate and it coughs/falls on it's face if I give it too much gas. The fastest it would go was maybe 60 and if there was an incline it would struggle to make it. So I'm trying to make it home because a tow costs 95$ here and the service engine soon light starts blinking. The light has been on for a while due to the bad cat but it just now started rattling. I make it about half way and the car dies. I come to a stop and crank it a few times and it starts. As I take off, it sounds like I can hear a loud hiss from underneath and after a mile or so the hiss went away. I drive maybe 40mph the rest of the way home and as I got closer to home, it drove better. When I got home, I popped the hood and it sounds like a hiss coming from the driver side of the intake manifold. I don't know for sure if this was always there or just started.
Could a bad cat cause all this? For a while, it felt like the emergency brake was on. Obviously it wasn't. Or did it just go into limp home mode?
ANY HELP GREATLY APPRECIATED!!!!

Honda Hunter

iTrader: (8)

Yes it's a bad cat. Paypal me please.

Alex94TAGT

Well, first off, I don't think there's any need to pay anyone. This is why we have forums in the first place.


-How old is the catalytic converter? It sounds obvious that the catalytic mesh within the cat has started to fall apart. In which case, the cat needs to be removed/replaced (or at least hollowed out for the time being). Since you have a 1996, you should have dual cats. If that stuff is falling apart, it's possible for it to clog & block exhaust flow, which will clearly affect engine operation.

-A "flashing" SES light typically indicates misfire detection, but I'd recommend having it scanned for any possible diagnostic trouble codes. If you have more codes, post them here. You mentioned a "catalytic converter code," which would seem accurate, but that might also indicate a possible problem with that post-cat oxygen sensor.


One step at a time -- I'd take care of that catalytic converter, and see where that takes you.

SS6ixSpeed

It's the original cat but it only has 70K miles. Regardless, I know the cat is bad because when I bang on it, I can hear a chunk bouncing around.
Being that it's an OBDII car, how would that sensor have anything to do with a misfire? I thought the only purpose of the sensor following the cat was to let you know a cat was bad.
Can I get by with a catco high flow without throwing codes? If not, what's a cheap cat that will work without issues? Catco doesn't recommend their cats on OBDII.

the_merv

iTrader: (88)

Them Sensors are going to read the exhaust and tell the Engine what to do. Now if there is no or barely any Exhaust going through, or parts of the Cat burning, the Sensor will get the wrong reading. Yea, that Cat is definately clogged if it's losing power..

Alex94TAGT

Correct. The post-cat sensors have nothing to do with fueling -- strictly there for monitoring the health of the catalytic converters (as you said). This would have nothing to do with a misfire -- I was merely pointing out that, if you did infact get a DTC code warning you of a catalytic efficiency problem (ie, P0420 / P0430), that would be more proof that the cat is shot.

If the catalytic converter was OK, I would be suspicious of the sensor itself.

That's all I meant.


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As far as what you can replace it with, I'm not entirely certain. Those things are kinda in a strange location/shape -- if you have the money, it might be easier to swap in a Random Tech y-pipe, which has the cats already installed. Otherwise, you might have a local exhaust shop work on it. Personally, I would try to replace both catalytic converters -- you have low mileage, but they are 10 years old. I believe you're allowed to replace them under Federal law after 5 years.

Do you have emissions testing in your area? I'm not too familiar with the quirks of the OBDII systems, but if a high-flow cat gave you trouble with those post-cat oxygen sensors, you could always run O2 sims... or get those DTC's programmed out of the computer.

wicked_95z

iTrader: (8)

My S-10 was acting the same way. I found out that the honeycomb inside the Cat had broken off and was actually cloggin the exhaust up. Real easy driving and it was fine. Anything more and it was like driving a 3 cylinder Dihaitsu.

James Montigny

iTrader: (13)

Sounds like an excuse to install a high-flow cat

Azthrei

This has happened to a buddy mine, cat got clogged and acted the same way as yours. Once he pulled it off, saw that it was plugged tight with ****. Once the new one went on, it was back up and running normal.

Fire67

iTrader: (3)

Here's the deal on the OBD2... You have 2 cats. One is bolted directly to the exhaust manifold on the drivers side, while the other is under the pass. side floorboard.
You cannot replace just one because a new one is bound to flow better than your old one thats still 'ok'. That would create more back-pressure on one side of the motor than the other.

Your options as I see em, assuming you have emissions checks where you live are:
1) replace both cats with factory replacements (means buying entire y-pipe)
2) get a random tech y-pipe with high flow cats already installed (this will bolt directly to your stock exhaust manifolds even with the funny drivers side flange)

OBD2 cars have a different type of catalytic converter than OBD1 cars, they clean the exhaust better and your post cat sensors will be able to tell the difference. This is why catco recommends against using their stuff on your OBD2 car. With the Random tech catted y-pipe, you pick up diameter and flow, but your O2's wont tell the difference.

If you dont live in and emissions check state like me, I would skip all of the above and gut both cats completely. Then get O2 simms or have the codes programmed out of the PCM. Or what I did was buy longtube race headers and off-road y-pipe outta summit(pacesetter).

Either way, the aftermarket options would probably be cheaper than replacing the stuff with a new factory y-pipe.

redgto04m6

First off cats dont go bad for no reason. If you replaced the fuel pump for reason of drivability then the cat coulda been damaged by the lack or lump of fuel(rich or lean). If so then just replace or remove the cats. If not then you may want to check the fuel injection flow and the ignition system. Basicly anything that can produce a rich or lean condition.Remember... something caused that cat to go bad! catalytic converters are very expensive and you dont just want to go throwing those kinda parts at it.

Jditlfm

iTrader: (26)

sometimes when a cat is cloged the car will sound like a vacuume cleaner and the exhaust will get supper hot, like cherry red.