Originally Posted by rex.effect
This entire post confuses me. I am WAY to ignorant on tuning values for it to make sense. Anyway, MY local shop in MD, says stay away from BP, Citgo, etc, and recommends Shell or Sunocco. I have a very strong suspicion that gas "quality" beyond the nitrogen enriched labels, varies greatly by region/ supplier. I think a compilation list, by region (and eventually local area), would make for a great sticky once more information can be provided
A list by region would be an interesting sticky, but you would need hard data for it to be worth anything unless you just trust the butt-dyno.
Basically those numbers above are saying that my car was pulling timing and detecting knock while on Chevron and Shell. Shell being the worst. Once I ran the tank of Shell down to 1/8th... I reset the ECU and filled up with 76. After a full tank of 76, all hesitation has gone away.
"Quality" of gas is really down to what extra stuff they put into it since they all get it from pretty much the same handful of refineries.
Another thought: With the economy being what it is and gas prices where they are, I also suspect that people are buying less premium than before. Brands that have 10% ethanol might not see as much premium going through their pumps... Ethanol tends to attract water. I guess the best bet is to make sure your station is always fresh.