Computers and Control Systems: Description and Operation

Engine Management Schematic:

Legend To Engine Management Schematic:

PURPOSE
The Bosch LH/EZL Computerized Engine Control system electronically regulates the air/fuel mixture, idle speed, and ignition timing to achieve optimum engine performance. Optimum performance means the best possible compromise between the demands of high power, low fuel consumption, and the cleanest possible exhaust emissions.

CONSTRUCTION
This engine control system uses five interconnected Electronic Control Units (ECU's); two controlling the fuel injection system, two controlling the ignition system and one controlling the electronic accelerator system.

The engine management system features self-diagnostics and fault code storage. All fault codes are accessed through the 38-pole diagnostic socket (X11/4) or the push-button with LED (X11/21s1).

SELF-DIAGNOSTICS
The self-diagnostic system is performed by the diagnostic module (N59). The module constantly monitors engine performance by comparing its programming "window" with the values it receives via the controller area network (CAN). When a programming parameter has been exceeded, a retrievable fault code is stored.

If the diagnostic module detects a serious fault in the engine control system, it activates the "CHECK ENGINE" light. By extracting the fault codes using diagnostic socket X11/4 or s1, you can determine what component or components need further testing or replacement.

FUEL INJECTION SYSTEM (BOSCH LH):
The two LH fuel injection systems are based on the Bosch multi-point fuel injection system with mass air flow sensor (LH-Jetronic). Two separate systems (one ECU per system) are used to operate the injectors. One system for cylinders 1 - 6 and the other for cylinders 7 - 12.

The ECU's use electrical input signals from various devices and sensors to calculate the engine load and condition. With this information they adjust the injection duration and timing to provide the optimum air/fuel mixture for performance, driveability, and emissions compliance.

ADAPTIVE MEMORY
Time and mileage affect the operation of both the injection and the idle control systems. To compensate for wear and deposit accumulation, the LH system modifies its basic programming (within a "window" of operation), to provide efficient operation under all driving conditions. If the system determines that it must modify its basic programming beyond the "window", a fault code is stored in the self-diagnostic memory.

LIMP HOME OPERATION
If an ECU determines that the mass air flow signal is incorrect, the system enters a pre-set "limp home" function. In "limp home" mode, a pre-set injection duration allows the vehicle to be driven to the nearest garage.

IGNITION SYSTEM (BOSCH EZL/AKR):
The two EZL ignition systems are based on the electronically controlled Bosch ignition system with knock control (EZL/AKR). Two separate systems are used to control ignition timing (one ECU per system). One system for cylinders 1 - 6 and the other for cylinders 7 - 12.

The ECU's use electrical input signals from various devices and sensors to calculate the engine temperature, load and speed. With this information the ECU's adjust the ignition timing to provide optimum performance, economy, and emissions output.

ELECTRONIC ACCELERATOR SYSTEM:
This engine control system is equipped with an electronically controlled accelerator pedal/throttle plate. The electronic accelerator ECU (N4/1), controls the idle speed. This system keeps the engine in a constant RPM range when at idle. The system will compensate for cold engine, high engine load or other influencing factors.