Engine Control Module: Description and Operation: Overview

EFI And Emissions Schematic (VIN 153560 - 0n):

NOTE: Jaguar made several mid-year production modifications during 1989, including change to a digital ignition system. When required, an explanation of significant differences will be provided.

The digital electronic control unit (ECU), located in trunk on right side, contains a microprocessor and separate electronic component circuits that interface with various input and output devices of the engine management system.

Incorporated into the ECU is a manifold absolute pressure (MAP) sensor used to detect engine load. It is made with a separate diaphragm system to measure and compensate for barometric pressure variations. The sensor is connected by a hose to intake manifold balance pipe.

The ECU performs primarily to regulate the fuel injection system. In order to maintain optimum air/fuel ratio, the ECU monitors exhaust gas oxygen content by way of input from a pair of oxygen sensors. When adjustments are needed, the ECU varies injector pulse width ("ON" time) as the means of controlling air/fuel ratio. Factors such as engine temperature, intake air volume and temperature, gear selector position and engine speed are also factored into ECU calculations. Starting with VIN numbers delineated under SYSTEM I.D., engine speed input is received from the digital ignition system, which is controlled by a separate ECU. Prior to this, engine speed information was obtained from the coil negative terminal via the ignition amplifier.