Chrysler Full-Size Trucks 1967-1988 Repair Guide

System Description


The Throttle Body Injection (TBI) system is used on 1988 V6-238 and V8-318 engines. The system is controlled by a pre-programmed digital computer known as the Single Module Engine Controller (SMEC). The SMEC controls ignition timing, air/fuel ratio, emission control devices, charging system and idle speed. The SMEC constantly varies all settings to meet changing operating conditions.

Various sensors provide the input necessary for the SMEC to correctly regulate the fuel flow at the fuel injector. These include the manifold absolute pressure, throttle position, oxygen sensor, coolant temperature, charge temperature, vehicle speed (distance) sensors and throttle body temperature. In addition to the sensors, various switches also provide important information. These include the neutral-safety, heated backlite, air conditioning, air conditioning clutch switches, and an electronic idle switch.

All inputs to the SMEC are converted into signals sent to the power module. These signals cause the power module to change either the fuel flow at the injector or ignition timing or both.

The SMEC tests many of its own input and output circuits. If a fault is found in a major system, this information is stored in the SMEC. Information on this fault can be displayed to a technician by means of the instrument panel power loss (check engine) lamp, or by connecting a diagnostic read out tool and reading a numbered display code which directly relates to a specific fault.