All fuel injected engines use the EEC-IV system. The Universal Distributor (EEC-IV) has a diecast base which incorporates an externally mounted TFI-IV ignition module, and contains a Hall Effect vane switch stator assembly and provision for fixed octane adjustment. No distributor calibration is required and initial timing adjustment is normally not required. The primary function of the EEC-IV Universal Distributor system is to direct high secondary voltage to the spark plugs. In addition, the distributor supplies crankshaft position and frequency information to a computer using a profile Ignition Pickup. The Hall Effect switch in the distributor consists of a Hall Effect device on one side and a magnet on the other side. A rotary cup which has windows and tabs rotates and passes through the space between the device and the magnet. When a window is between the sides of the switch the magnetic path is not completed and the switch is Off, sending no signal. When a tab passes between the switch the magnetic path is completed and the Hall Effect Device is turned On and a signal is sent. The voltage pulse (signal) is used by is EEC-IV system for sensing crankshaft position and computing the desired spark advance based on engine demand and calibration.
The heart of the EEC-IV system is a microprocessor called the Electronic Control Assembly (ECA). The ECA receives data from a number of sensors, switches and relays. The ECA contains a specific calibration for peak fuel economy, driveability and emissions control. Based on information stored in its memory, the ECA generates signals to control the various engine functions.
The ECA calibration module is located inside the ECA assembly. The calibration module is called a PROM.
On all vans, the ECA is located inside the truck on the left of the firewall, behind the kick panel.
A potentiometer senses the position of the vane airflow meter in the engine's air induction system and generates a voltage signal that varies with the amount of air drawn into the engine. A sensor in the area of the vane airflow meter measures the temperature of the incoming air and transmits a corresponding electrical signal. Another temperature sensor inserted in the engine coolant tells if the engine is cold or warmed up. And a switch that senses throttle plate position produces electrical signals that tell the control unit when the throttle is closed or wide open.
A special probe (oxygen sensor) in the exhaust manifold measures the amount of oxygen in the exhaust gas, which is in indication of combustion efficiency, and sends a signal to the control unit. The sixth signal, crankshaft position information, is transmitted by a sensor integral with the new-design distributor.
The EEC-IV microcomputer circuit processes the input signals and produces output control signals to the fuel injectors to regulate fuel discharged to the injectors. It also adjusts ignition spark timing to provide the best balance between driveability and economy.