[LT7A]

You might want to post this in the engine part of the forum too, but folks in this part are more familiar with your specific engine. I was going to recommend a liquid engine treatment to clean carbon out of the combustion chambers like Seafoam or Berryman B-12 Chemtool and I was not really tracking with the idea of the lean condition that MikeB mentioned. I figured carbon buildup was effectively raising your compression ratio by taking up space in the combustion chamber -- not uncommon. But more pinging in cooler temperature seemed opposite of what should happen. So I thought about Mike's assertion that there might be a lean condition. The vaporization of gasoline is part of what cools the mixture as it goes into the combustion chamber and so if there is denser air, i.e. a higher oxygen to fuel ratio, more pinging is conceivable. Another note is that your engine isn't particularly high mileage either. Let us know what your plugs look like, post pictures if you can. I'm thinking that you may need at least a carburetor adjustment or maybe a rebuild. If you can swing it, new plugs, cap and rotor, plug wires if possible, then have the carb rebuilt and get it tuned. You'll get a better tune with the new parts and probably save in the long run with the distance you drive. You should be able to go back to 87 octane and be burning less of it on a good tune. My personal preference would be to run good gas (Chevron where I live, or Shell if no Chevrons close enough) since the Techron in Chevron gas is an effective cleaner, and then run a reputable fuel system cleaner every few tanks. That way you are also chipping away at any potential problems of carbon buildup. My guess is that your carb is the main source of the problem assuming your timing is on, and that carbon may have been a secondary contributor. Let us know how it goes. Thanks