Bad cat?

[JDanW]

My wife's '98 Q45 has developed the rotten egg smell and after researching it, it seems to be the catalytic converter. We have been running regular unleaded, as the car dealer said it was OK. We have the CEL on for quite some time, but nothing seemed wrong enough to be concerned about. No need to bash me too bad, but a few answers and help would be appreciated...

1) Does lower octane gas vs. premium higher octane affect the CATS?

I understand the more likely situation, is maybe a bad O2 sensor or 2 or 4 causing it to run rich, which overwhelms the CATS. If this is the case, and we get the car running properly, with new sensors, or whatever it takes...

2) Can the CATS be "saved"? i.e. running properly, can they overcome the situation that they are in? Is there some "extra capacity" to what they do, that they can handle normal exhaust and undo any saturation or whatever of sulfer?

TIA...JDanW

[qship96]

First things first. Have the engine codes read with a obd2 scanner,most auto parts stores will read them for free for you-the codes will lead you directly to the reason your light is on,fix that problem and see where you stand. Guessing only leads to throwing money at parts,that may not even be faulty,like your converter.

use premium fuel,as the manufacturer recommends......

[BadQ45t]

2nd running super unleaded....your were told the wrong information. Get the scan before you start to replace parts, these ODB2 cars are very smart and will tell you what is wrong 99 times out of 100. You probably damaged your 02 and knock sensors with lower grade fuel, but get it scanned so you can figure out exactly what is wrong.

[elwesso]

Theres really no way to damage the knock sensors or o2 sensors by running unleaded fuel. The dealer is right, it won't do any damage but it certainly isn't going to make anything better. I would recommend ALWAYS running premium wherever recommended, it only costs like an extra $2-$4 a fill up so why not do it? Could probably forgo a McDonalds coffee for that...

One thing I've noticed is if you do a lot of short trips that can cause the smelly exhaust. What causes it is moisture mixed along with the sulfur in gasoline, so if you're only doing short trips (maybe <10 miles) every time the car starts up there could be residual moisture in the exhaust.

Otherwise, it could be the cat failing but I've not heard (on here) of too many Q45's having secondary cat problems.

[JDanW]

Well, I appreciate all the GOOD advise. Most I knew... get it checked out and stop speculating...posting this just so there is a resolution and something to search on...

It seems the alternator i replaced a few months ago, went bad and was overcharging the battery, which causes the sulfur smell. Codes were the knock sensor and another, unrelated to the smell.

We will start with the premium gas and try to preserve the Q.