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  #1  
Old 08-03-2007, 10:28 AM
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budbaer budbaer is offline
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Not Exactly High Octane

Recently I have had a octane knock at low RPM's. I have tried just about every fuel system cleaner on the market with very limited if any results. Yesterday I tried 104 Octane's Maximum Octane, the first actual octane boost product I've used. Now I have no knock and greatly improved performance. I don't understand because I only use 93 octane or higher in my car and I have never had a knock until this summer. Is it possible that gas station is charging me for premium gas and selling be a lower grade? Is there anyway that I can test the octane level of the gasoline that I buy? Any input would be greatly appreciated and I welcome all opinions.
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Old 08-03-2007, 11:08 AM
dcarrb dcarrb is offline
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Showing my ignorance: Aren't properly-functioning knock sensors supposed to adjust ignition timing to prevent this sort of thing?

I used to run premium to keep my totally-ordinary 1990 Legacy from knocking; figured it was a relatively minor concession to its old age. Carbon deposits on the pistons, said the mechanic. In the SVXs I'm using an increasingly large percentage of 87 octane (still topping-off with 93), and both cars seem quite content.

dcb
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Old 08-03-2007, 11:53 AM
Kelvin Kelvin is offline
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Quote:
Originally Posted by budbaer
Recently I have had a octane knock at low RPM's. I have tried just about every fuel system cleaner on the market with very limited if any results. Yesterday I tried 104 Octane's Maximum Octane, the first actual octane boost product I've used. Now I have no knock and greatly improved performance. I don't understand because I only use 93 octane or higher in my car and I have never had a knock until this summer. Is it possible that gas station is charging me for premium gas and selling be a lower grade? Is there anyway that I can test the octane level of the gasoline that I buy? Any input would be greatly appreciated and I welcome all opinions.
Carbon buildup can cause increased compression, which would result in knocking. If I were you, I'd go to the hardware store, and by a gallon of either Xylol or Toulene, and dump half of it in your next tank, and the other half in the tank after that. A large percentage of gasoline is toulene/xylol anyway, and this will function exactly the same as a fuel system cleaner, but it will work better, and a lot cheaper. Plus it boosts your octane like crazy, and my SVX felt quite a bit faster with it.
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Old 08-03-2007, 02:54 PM
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Unleaded

I have always run just play old regular unleaded in ALL of my SVXs and have never had a one of them knock. I suspect you have some problem other than just the fuel. Before you say it, one of them has over 200K miles (in family for over 12 years) and is running strong and not burning oil or making any strange noises.

Lee
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Old 08-03-2007, 08:26 PM
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Knock sensors should compensate for lower octane gasoline, they would only throw a code though if they arent functioning - but your problem goes away when using race gas with higher octane
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