The Neighbourhood Mechanic: What's the right octane?

In an effort to meet the demands of the newly regulated government emissions standards, car manufactures were forced into abandoning the reliable carburetor for the new and yet untested electronic fuel injection system. All this occurred in the mid-80s. I find it hard to believe that it was over 20 years ago. As computing power increased, so did the level of sophistication of the EFI system. EFI systems no longer relied on preprogrammed maps, but the computer was able to react to its environment. Simply put, cars had the ability to think. Drivability improved, fuel economy improved and emissions improved. All this adjustability had other benefits too. The engine management system has the ability to adjust for “bad gas.” If the octane level is too low the computer could draw back on the timing and adjust the duration of the injectors, avoiding ping and lessening the chance of damaging the engine. Result, drivability was not drastically affected by the use of an improper grade of fuel. Check your owner's manual for the grade of fuel that you should be purchasing. You may actually be buying more gas than you need. Regular is 87 RON, while premium is usually 91 RON.

Q. We are all looking for a way out of paying at the pumps. The manufacturer of my vehicle (Mazda) recommends using mid-grade or higher. The average fill is $65-70. My strategy is to fill half the tank with regular gas and half with mid-grade, supplementing the fuel system with an additive/cleaner every third tank. Do you see this strategy as being a workable solution?
Looking For Relief


A. Your car should run happily on regular. No fuel additive is required. The vehicle's computerized injection system will make the necessary adjustments to the timing and injection pulse. If you notice any “pinging” under acceleration switch to mid-range. I doubt that you will notice any change in drivability.