Speed Density System

SPEED DENSITY SYSTEM
The Throttle Body Fuel Injection (TBI) is a speed and air density system. This system is based on "speed density" fuel management.
Three specific data sensors provide the control module with the basic information for the fuel management portion of its operation. That is, three specific signals to the control module establish the engine speed and air density factors.

SPEED
The engine speed signal comes from the Distributor Ignition (DI) control module to the control module on the crank reference high, CKT 430. The control module uses this information to determine the "speed" or RPM factor for fuel and ignition management.

DENSITY
Two sensors are used for the density factor, the Engine Coolant Temperature (ECT) and the Manifold Absolute Pressure (MAP) sensors.
The ECT sensor is a 2-wire sensor that measures the temperature of the engine coolant. The ECT sensor is a thermistor which changes its resistance based on temperature. When the temperature is low, the resistance is high, and when the temperature is high, the resistance is low.
The Manifold Absolute Pressure (MAP) sensor is a 3-wire sensor that monitors the changes in intake manifold pressure which result from changes in engine load. These pressure changes are supplied to the control module in the form of analog electrical signals.
As intake manifold pressure increases, the air density in the intake manifold also increases, and additional fuel is required. The MAP sensor sends this pressure information to the control module, and the control module increases the amount of fuel injected by increasing the injector pulse width. Conversely, as manifold pressure decreases, the amount of fuel is decreased.
These three inputs MAP, ECT, and RPM are the major determinants of the air / fuel mixture delivered by the fuel injection system.
The remaining sensors and switches provide electrical inputs to the control module which are used for modification of the air / fuel mixture, as well as for other control module control functions, such as Idle Air Control (IAC).