seasonal changes
There are two or three issues you may be dealing with.
1. There are seasonal changes in the gasoline blends, each major metropolitan area changes from winter to summer blends at different times due to local climate. There are also changes due to the seasonal requirements for oxygenates in some areas to control winter emissions.
2. The detonation sensitivity will go up as summer temperatures peak. If you set up your system during cool weather, you may have to turn up the injection rate or pull back timing a bit when it gets very hot. Once you get a tune that works in very warm weather you should not have to change its settings much except in very cold weather you might be able to either turn it off, or cut back the injection rates.
3. Due to the recent high gasoline prices the refineries may be adjusting the fuel blends to keep costs down. They are required by law to hit an average R+M/2 octane rating as posted on the pumps but they have some latitude in how far apart the Ron and Mon numbers are while still hitting the advertised AKI. High compression high performance engines and supercharged, turbocharged engines are more sensitive to the Motor Octane Number, so if they increased the difference between the Ron and Mon to use cheaper blending stocks it might show up in high performance engines but be perfectly acceptable in your average car.
You may want to experiment with a different brand, of fuel, they each blend a little differently.
Larry
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