The engine timing system on a gasoline automobile works by providing a spark to ignite the compressed fuel at the right time, providing the maximum power from the expanding fuel. If the engine timing is not correct, the vehicle suffers a loss of power, uses more fuel and produces more emissions.
In early automobiles, the driver adjusted the engine timing as he drove. He moved a lever that advanced or retarded the spark so the engine ran as smoothly as possible. Later vehicles used a rotor, points and condenser. The shaft of the rotor had ridges that lifted the points, opening the gap like a switch. When the points closed, electricity flowed to the spark plug to provide the ignition spark. The vacuum of the engine advanced and slowed the spark.
As of 2015, most vehicles use an onboard computer to set the ignition timing. The computer gathers data from several different sensors on the engine and exhaust system to adjust the spark so that the plug fires at the proper time for the cylinder. Most of the computerized systems have greater fuel efficiency due to a better timing system. These systems do not use points but follow the position of the piston and adjust the spark as necessary for greatest efficiency.