Will Moderate For Cigars
Date registered: Apr 2005
Vehicle: 2002 ML320, 2005 S430 4MATIC, 2010 F150 Crew Cab
Location: City on the TN River
Mentioned: 3 Post(s)
Quoted: 210 Post(s)
RE: Gas octane ratings
From what I understand about this, high octane fuel (91 and up) burns slower and cleaner while lower octane fuel burns faster and dirtier. The dirtier burning fuel lends to the carbon build up on pistons. The resulting effect seems like an oxymoron, purer burning cleaner but slower and cheaper burning faster but not clean (the faster the explosion, the less efficient the combustion of fuel). This results in minute amounts of carbon and raw gas being forced into the catalytic converter which clogs and damages it (a bad converter many times will smell like sulfur burning). This is also why engines will knock with cheaper fuel. There are actually 2 explosions taking place in the chamber which results in the effect of a hammer hitting the top of the piston giving it the metallic sound.
While the engine timing is adjusted to compensate for knock, hence allowing the fuel to burn cleaner, buying cheap fuel isn't in no way good for a car designed to run high octane. While many folks run cheap fuel in their vehicles, when 91 or higher is required, without noticeable damage, there are the many who are just as unlucky and damage their engine.
If running cheap fuel, I would definitely be more concerned with what it might do to my engine more than the converter, since the computer does compensate somewhat for low octane.
There are many other things that can damage your catalytic converter as well such as:
1. Driving with a bad O2 sensor
2. Plugged injectors (causes unburned gas to ignite in the converter, thereby damaging it)
3. Piston Blow by
4. Leaking head gasket
5. Fouled or bad plugs
6. Bad intake gasket
I am by no means an expert, but I hope this helps! [:)]