Is it more likely for a car to pass a smog test with gas of a low octane level such as 87 or of a high octane level such as 91? Or does it even matter?

I doubt octane rating will affect your emissions much but I don't know for sure. What definitely will help is to get some methanol and mix it in with your gas. I've mixed it 3 parts gas to 1 part methanol and being an oxygenated fuel it lowers your emissions.

Originally posted by Marck

Is it more likely for a car to pass a smog test with gas of a low octane level such as 87 or of a high octane level such as 91? Or does it even matter?

 

Unless you have a higher compression ratio. The higher the octane the slower the burn.

Ron

I just took another smog test today. It failed again. This time I got 197ppm for the HC at idle. Back in April I got 1011ppm for the HC at idle. So at least it improved. I need to have 120ppm of HC or less to pass. My car passes on all the other tests. I replaced the oxygen sensor, spark plugs, ignition coil, spark plug wires, fuel filter, oil, oil filter, air filter, thermostat. PCV is new since December of 2002. I put some Redline fuel system cleaner in. I checked the EGR and it is good. The only thing I think I have not replaced is the cat. What am I missing? I think I am ready to give in and use something else besides 91 octane gasoline. So is methanol or ethanol too corrosive? Which should I use? Will it ruin anything such as my cat, new O2 sensor, or EGR. Where do I get it? What other options do I have????????????????

 

BTW, this is for my sube in my signature.

HC is Hydrocarbons, which is raw fuel. You are running rich in other words. Check your fuel system, and your fuel pressure regulator. Bad cat MIGHT do it, since that is one of the things that the Cat scrubs from your exhaust. Another thing that can do it though is if oil is sneaking into the exhuast, from worn rings, or valve stem seals. There is some "emissions reducer" crap you can get from the store, that in most cases is guaranteed to make your car pass or they pay for the test or sumpin.

 

My auto teacher told me something about running the car a quart low on oil and putting like, a cup of Formaldehyde in the gas tank??? He said something about it eventually damaging the motor, but ti will pass emissions.

Methanol is used as one of the components for oxygenated fuel. It's used in Utah for the winter months by EPA regulations. The gas stations use up to 15% MTBE or methanol. It doesn't hurt any of the components on your car or they couldn't use it. It does however clean the crud out of the fuel system so the first time you use it there's a chance you might clog up your fuel filter a bit.

One thing that will help is to get the cat good an hot. Take it for a 5 mile or so blast down the freeway in a lower gear to keep the engine in the 3000 to 3500 range. If there is a long line at the test station don't wait in line, keep driving around untill the line gets short.