Computerized Engine Controls: Sensors

The computer receives information from its sensors. Most sensors are simple sending units that are either grounded or open (like an oil pressure switch) or provide a varying resistance (like a fuel gauge sending unit). Some engine data comes from existing sensors (engine temperature) or a connection to an existing circuit (coil or distributor pick-up).

On some systems (Ford EEC), the computer sends a reference voltage out to each sensor. Varying resistance in the sensor drops the voltage a certain amount, and the computer uses the return voltage as a signal.

Computer decisions are based on the pre-programmed information put in by the manufacturer and sensor input. The most common sensor inputs include:

• Air/Fuel Ratio (from oxygen sensor)
• Engine Speed (from distributor or crankshaft sensor)
• Engine Temperature
• Engine Load or Vacuum
• Throttle Position

Other sensors are used by some systems to provide additional information. Some of these are:

• Intake Air Temperature
• Intake Air Flow
• Barometric/Manifold Pressure
• Vehicle Speed
• Fuel Temperature and Pressure
• Detonation
• Transmission Gear Position

Two different systems may both require the same input, but use different sensors to obtain it. For example, one of Ford's MCU systems uses an Idle Tracking switch to tell the computer when the throttle is against the idle stop. Another MCU system uses a vacuum switch which provides the same information. In spite of the variety of sensors, computers make their decisions based on the same kinds of inputs.