Section 33 (EEC IV Theory/Operation): Description

Because of the volume of information and the size of the article, the EEC-IV article is divided into 4 articles and will be in this section as applies to the vehicle:

• Description, Operation and Pre-Test Instructions for all models.
• 2.8L Testing and Diagnosis.
• 4.9L Testing and Diagnosis.
• 5.0L and 5.8L Testing and Diagnosis.

For specific model DIAGNOSIS & TESTING procedures, see the appropriate EEC IV TESTING article in this section.

The center of the EEC-IV system is the Electronic Control Assembly (ECA). The ECA receives information from various sensors and switches. Based on information received and the operation program in the ECA's memory, the ECA generates output signals to control engine operation. The calibration module for EEC-IV system is mounted inside the ECA. The ECA is located in the passenger compartment, in one of the following locations: under the center console, under dash on left side of steering column, under passenger seat, or under dash behind right kick panel.

The EEC-IV system controls 3 major areas of engine operation: Air/fuel mixture, ignition, and emission control. Additionally the system can control A/C compressor clutch operation and idle speed. The system provides self-diagnostic capabilities.

The air/fuel mixture control is accomplished by use of a feedback carburetor. The ignition system is controlled by the ECA through a Thick Film Ignition (TFI-IV) module. Ignition timing (advance or retard) and dwell are controlled with this system to improve ignition system performance.

Emission control components controlled by this system include EGR and canister purge. These systems are normally off, but are turned on when the engine is ready to operate with the mixture change caused by EGR and canister purge operation.