Three types of timing are used for gasoline engines. Static timing establishes a physical relationship between engine crankshaft position and the distributor. This is fixed and should not change. Computer assisted vehicles use various sensors to modify the computer controlled timing program. The timing program changes are the equivalent of centrifugal and vacuum timing devices formerly used.
Computer controlled engines change timing more rapidly than mechanical systems.
Computer systems are more closely attuned to optimum timing points than the former mechanical devices. Optimum timing results in optimum fuel economy and reduced tailpipe emissions. Some manufacturers have field serviceable computer calibration chips. These chips modify the computer program and profile for that particular vehicle with specified accessories and equipment. If a vehicle has an improperly calibrated chip, reduced power, lowered mpg, and poor driveability may result.