Gasoline Octane amount and Hydrocarbon level in exhaust

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I recently went to my Maryland state emissions test. My vehicle failed the "hydrocarbon" part of the test.

Our state standard is: 2.8000 GPM
My vehicle came in at: 3.0080 GPM

I usually take the test with a tank of "93 octane" gas, and I have always passed. This time I took the test, with a tank of "89 octane" gas, and failed.

For this question, I'll assume that the engine and emissions system are working properly.

I wondered whether the octane amount in the gas would influence the amount of hydrocarbons in the exhaust?

Does higher octane mean less hydrocarbon emissions in the exhaust?

Should you always take an emissions test with "93 or 94" octane gas?

Does the brand of gas effect hydrocarbon levels?


Any ideas anyone?
Thanks in advance!
 
I'd heard the opposite, that using too-high octane will *increase* emissions.
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For example, from http://www.dragtimes.com/race-gas-fuel.php...

Premium Gasoline
Certain high performance engines benefit from use of high octane fuel. For other engines, using a fuel with a higher octane rating than the vehicle requires sends unburned fuel into the emissions system and catalytic converter. This puts unecessary stress on the emissions system. For some vehicles, a rotten egg smell coming from the tailpipe signals use of too-high octane gas.
 
It's not the gas.
Normal wear and increasing inefficiency are the cause.
Get a good tune up, clean your injectors, change your oil and filter, and increase your tire pressures to the max.
Posssibly a new O2 sensor or cat convertor is necessary.
 
Assuming that the octane had something to do with it, the only way I can see it affecting emissions would be with the following conditions:

1) Your vehicle has an operational knock sensor.
a) The knock sensor detected a knock due to insufficient octane
b) The computer retarded the timing because of the knock sensor detecting knock
c) Incomplete fuel burn resulted from the retarded timing (which is why one gets lower fuel economy on vehicles with bad knock sensors where timing is defaulted to the retarded profile). If I'm not mistaken, this would raise hydrocarbons in the exhaust.

or

2) Your vehicle has a knock sensor that is defective, resulting in "c" above

I don't know how much a Maryland inspection costs, or the procedures that may limit the number of tests allowed (I don't have emissions testing here in Louisiana). But you may be able to pass it simply by using a higher octane gas (if your car recommends it). I've also read that one should fully warm up the car before having an emissions test done. This ensures the cat(s) are warm enough to function properly. If you have a FSM or Haynes for your car, there are ways to test a knock sensor (basically just checking the resistance, and comparing it to the specs in the book).

This is all assuming that the lower octane had something to do with it. It's possible you have something else wrong with the car, like O2 sensors or such. It would help to know what kind of car, mileage, maintenance, etc to help troubleshoot better.

Dave
 
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