The car is a 92 RS 5.0 TBI. The car has a k&n air filter, edlebrock shorty headers, and a 3in flowmaster cat back exhaust. The car is complete stock other than those few mods.

And on a side note it keeps going through muffler(s) and catalytic converter(s) but it is a single cat/muffler car.

Two years ago it failed a smog check for the first time. My dad was told the cat was bad so he replaced it and retested and failed. He then replaced the muffler too and barely passed, I do mean barely. Two years later now and the flowmaster muffler has begun to sound horrible, as though something has come loose inside of it. There is a loud rattling sound coming from inside the muffler. WTF!

Unfortunately smog check time has come around again and the car once again has failed. So before we put any money into the car I am here to find out what ya'll think. What exactly is causing these problems with the cat and muffler, and why is the car failing the smog test. Should I waste more money and put a new muffler on; perhaps a new cat too? I don't understand why these two components keep failing and exactly what do I do?

Any help is much appreciated guys, thxs.

P.S. I am in S.Cali for those of you who are interested.

 

what did it fail on?

 

The only info I got from my dad was that the tech said the after market cat was most likely the culprit for the failure. The tech said that most after market cats don't last long, but I disagree with that statement.

I am most curious about the muffler. It's a near new muffler, maybe a year old. So how could it have went bad?

If I can get the smog test results I will post them; however this is all the info I have as of right now.

Thnx again.

 

When was the last time you replaced the O2 sensor? Is your EGR working? When was the last time you gave the engine a full tune-up?

I had the same problem, I failed smog. I replaced the O2 sensor, the EGR valve, the plugs, cap and rotor, and the cat. After that, it passed with flying colors. Hint, the cat only works when it's HOT, so drive the car around for a while before taking it to the inspector, to make sure the cat is pre heated.

Also, you might want to run some fuel system/injector cleaner through it first. Go with the Chevron Techron or Gumout Regaine, they are the best.

 

First step is to drive around with a scanner and see what is going on. o2 seem to be crossing ok? blms ? etc. Any codes?

Could be a fault o2, egr, etc like mentioned, but without data your just gonna be replacing things until something seems to cure it.

-- Joe

 

I've also heard that too free flowing of an exhaust on the TBI cars will not have enough pressure to actuate the EGR since it doesn't use a negative backpressure EGR. A friend of mine had to swap to a stock muffler to get his EGR to work and hence, pass.

 

Knowing what it actually failed for would REALLY help figure it out. Without that, you could be wasting your money; or possibly even doing things that might make it worse. For example, EGR has essentially zero effect on CO or HCs; so if that's what it failed for, you can play with the EGR valve from now till Judgement Day, and it will never get any better.

It's easy to tell somebody, go to the dealer and spend 3 times as much for OE parts as you can buy them for elsewhere; funny thing is, there's ALOT of us (including myself) that have had NO TROUBLE WHATSOEVER getting cars through "enhanced" CA inspection, even with significant mods.

Best place to start, is the simple tune-up type stuff; spark plugs, cap & rotor, and wires if they're really old, and DEFINITELY a new O2 sensor.

Typical cat problems are caused by backfiring in the exhaust, blowing the catalyst to bits, which then gets blasted out the back of it into the muffler where it gets stuck and makes rattling noises. That in turn is often caused by a rich condition on decel, which is caused by a bad O2 sensor. That one sensor is utterly critical to the ECM's mixture control; it's its "eyes" on the results of whatever decisions about mixture that it's making. If the ECM is getting bad feedback from the O2 sensor, for example if the sensor says "lean" when the exhaust is really not lean, you'll end up with too much fuel, and all the other symptoms you describe will follow.

 

Ok, I have the smog test paperwork.

Here's where it failed:

HC(PPM)

MAX/ AVE/ MEAS

110/ 31/ 143
85/ 20/ 107


Everything else passed. The cat has pass(ed) next to it, so the tech saying the cat was the problem was BS.

 

normally high HC is caused by a misfire, but it can also be caused by a vacuum leak, or the engine running too lean or too rich along with some other things.
if you put a cheap cat on it, it could very well be bad, the cheap cats seldom last very long & they seldom clean the exhaust emissions as good as a factory cat does. the rattle from the muffler could be caused by the cat coming apart.

follow the advice above & check everything out, see if you find anything wrong, as was said, you may have a problem that caused the cat to go out sooner than it normally would have.

the cat passed the visual inspection,.. meaning they looked under the car & saw it, whether it works as it should or not is another thing.

 

When the inspector marks "pass" for the cat, that merely means that its presence was observed visually. It doesn't mean that it's any good.

If CO was within tolerance but HCs were out, then it's almost certainly an ignition system problem.... allowing unburned fuel to pass through.

If it was an actual fuel problem causing it to fail, like faulty injectors or O2 sensor or whatever, then the CO would have been sky-high too.

 

Yeah the " CO " was fine it's the " HC " that had major problems. So you are saying that for sure that it's an ignition problem; cause that will be where I start at if so.

I am also going to take the advice on a tune up, I'll be doing it asap.

 

Yeah, start with a tune up. Replace the O2 sensor with a Delco unit, not Bosch. Then get a pre-test so you can see where you're at (so you don't fail again).