1980 Cadillac Throttle Body

The 1980 Cadillac Eldorado and Seville was equipped with a throttle body injector system.

Also known as the DEFI, which monitors engine operating conditions such as temperature and engine load and electronically meters fuel to achieve desired air/fuel mixtures for exhaust emission control and driveability. This is done by the ECM, electronic control module, or computer.

The EMC signals the fuel injectors in the throttle body injection (TBI) unit to provide the correct quantity of fuel for a wide range of operating conditions.

Various sensors are used to monitor prevailing engine conditions and are electrically connected to the ECM. Each sensor operates independently of the others. Each sensor transmits a signal to the EMC advising of specific engine conditions and this information is continually up dated by the ECM. The ECM analyzes all signals received and transmits appropriate commands. The sensors include the Manifold Air Temperature Sensor (MAT), Engine Coolant Temperature Sensor, Manifold Absolute Pressure Sensor (MAP), Barometric Pressure Sensor (BAR), Throttle Position Sensor (TPS), and engine speed sensor which is provided by the Electronic Spark Timing (EST) distributor.

As an example of sensor input to the ECM, the amount of air entering the engine is measured by monitoring intake manifold absolute pressure (MAP), manifold air temperature, and engine speed (in RPM). This information allows the ECM to compute the flow rate of air being inducted into the engine and, consequently, the flow rate of fuel required to achieve the desired air/fuel ratio for the particular engine operating condition. In other words, the ECM performs high speed calculations and converts this multi variable input information into an injector electrical pulse width which opens the injectors for the proper time with respect to the cylinder firing sequence. Also the system automatically compensates for higher altitudes by the design of the Fuel Pressure Regulator and by the information received by the electronic Control Module from the Manifold Absolute Pressure Sensor (MAP).

The significant difference between the DEFI system and the Computer Controlled Catalytic Converter system is that the DEFI system does not include and oxygen sensor in the engine exhaust. Thus, the ECM, receiving other sensor information, calculates the required air fuel mixtures and pulses the fuel injectors for the particular engine operating condition.

The throttle body injection (TBI) assembly is centrally located on the intake manifold where for simplicity, air and fuel are distributed through two bores in the throttle body to the intake manifold similar to a normally carbureted engine. The throttle body is made of aluminum and consists of a housing with two bores of 42.86 mm to provide sufficient air capacity at higher air flows for power requirements. Air for combustion is controlled by two throttle valves, one for each bore, connected to the throttle shaft and lever assembly operated by the accelerator pedal linkage. The end of the throttle shaft, opposite the throttle lever, includes a lever that controls the throttle position sensor.

Fuel for combustion is supplied through two fuel injectors, one for each bore, mounted on the TBI assembly with the metering tip located directly above the throttle valves. The injectors are electrically pulsed or timed open or closed by the Electronic Control Module and normally are actuated alternately according to the engine firing order. The ECM receives inputs from the various sensors concerning engine operating conditions, performs high-speed calculations of engine fuel requirements, and pulses or times the injectors, open or closed, for precise deliver of fuel to each bore.

Updated on 12/01/2021

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