All gasoline engines through 1976 are designed to operate on leaded fuel of 91 research octane or higher, sold as Regular gas. All 1977 and later Mazdas sold in the U.S. use unleaded fuel of 91 research octane or higher. Regular leaded fuel may not be used in these models, because they are equipped with a catalytic converter for emission control purposes. Leaded fuel will render the converter useless, raising the emission content of the exhaust to illegal and environmentally unacceptable levels. It will also block the converter passages, increasing exhaust back pressure; in extreme cases, exhaust blockage will be raised to the point where the engine will not run. Most 1977 and later Mazdas sold in Canada are able to use regular fuel; however, converter equipped models must use unleaded fuel. In either case, fuel used in Canadian models must also have an octane rating of 91 or higher (research method).
Fuels of the same octane rating have varying anti-knock qualities. Thus if your engine knocks or pings, try switching brands of gasoline before trying a more expensive higher octane fuel. If you must use unleaded fuel, this may be your only alternative.
Your engine's fuel requirements can change with time, due to carbon buildup which changes the compression ratio. If switching brands or grades of gas doesn't work, check the ignition timing. If it is necessary to retard timing from specifications, don't change it more than about four degrees. Retard timing will reduce power output and fuel mileage and increase engine temperature.
The diesel engine in your Mazda is designed to run on No. 2 diesel fuel with a cetane rating of 40. For operation when the outdoor air temperature is consistently below freezing, the use of No. 1 diesel fuel or the addition of a cold weather additive, is recommended.