Computers and Control Systems: Description and Operation
PURPOSEThe Bosch LH/EZK Computerized Engine Control system (CEC) 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
The system uses two interconnected Electronic Control Units (ECU's); one controlling the fuel injection system and the other controlling the ignition system.
Both systems feature self-diagnostics and fault code storage. Fault codes are accessed through a common diagnostic socket. The LH-2.4 fuel control system also features adaptive programming functions to compensate for the effects of time and mileage. Because the system is adaptive, no adjustments to fuel mixture, idle speed, or timing are necessary.
Fuel Injection System Schematic:
FUEL INJECTION SYSTEM (BOSCH LH2.4-JETRONIC):
BOSCH LH2.4-JETRONIC stands for:
BOSCH = manufacturer
L = luft (German for air)
H = heiss (German for hot as in hot-wire)
2.4 = model series
The LH fuel injection system is based on the Bosch multi-point fuel injection system with hot-wire mass air flow sensor (LH-Jetronic). The ECU uses electrical input signals from various devices and sensors to calculate the engine load and condition. With this information it will adjust the injector frequency to provide optimal air/fuel mixture, performance, driveability and emissions output.
Several notable features of the LH-2.4 fuel system include:
^ Adaptive memory,
^ Self-diagnostics with fault code storage,
^ "Limp home" operating mode,
^ Separate cold-start injector, and
^ Anti-knock enrichment.
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-2.4 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.
SELF-DIAGNOSTICS
The self-diagnostic system is a built-in function of the injection ECU. The ECU constantly monitors engine performance by comparing its programming "window" with the values it receives from various sensors. When a programming parameter has been exceeded, a retrievable fault code is stored.
If the self diagnostic circuit ("on board diagnostics") in the ECU detects a serious fault in the fuel injection system, it activates the "CHECK ENGINE" light. By extracting the fault codes using the diagnostic socket, you can determine what component or components need further testing or replacement. Federal and Canada market vehicles can store up to three fault codes, California market vehicles can store up to 17 fault codes.
LIMP HOME OPERATION
If the ECU determines that the mass air flow sensor 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.
COLD START INJECTOR
During cold weather starting additional fuel is delivered to the intake manifold by an electrically operated cold start injector.
ANTI-KNOCK ENRICHMENT
If ignition knock cannot be counteracted by retarding ignition timing, the fuel system ECU provides a richer mixture to reduce combustion temperature.
ECU INPUTS AND OUTPUTS
Input devices (the ECU receives):
^ Battery supply signal (voltage).
^ Ignition switch signal.
^ Oxygen sensor (lambda sond) signal.
^ Crankshaft speed signal from the ignition control unit.
^ Speedometer signal.
^ Crankshaft position signal from the ignition control unit.
^ Knock signal from the ignition control unit.
^ Coolant temperature signal.
^ Air mass meter signal.
^ Gear selector signal (automatic transmission only).
^ Throttle position signal.
^ A/C switch signal.
^ A/C pressure sensor signal.
Output devices (The ECU controls):
^ [1][2]System relay ground.
^ Suppressor relay by controlling the [1][2]system relay.
^ Fuel injector ground.
^ Cold start injector ground.
^ Idle air valve.
^ Air mass meter signal to the ignition system control unit (ignition ECU input device).
^ Shift indicator light (manual trans. only).
^ Diagnostic socket fault information.
^ "CHECK ENGINE" light.
Ignition System Schematic:
IGNITION SYSTEM (BOSCH EZ116K):
BOSCH EZ116K stands for:
BOSCH = manufacturer
E = elektronische (German for electronic)
Z = zuendung (German for ignition)
116 = model series
K = klopfregelung (German for knock control)
The EZK ignition is based on the fully electronically controlled Bosch ignition system with knock control. The ECU uses electrical input signals from various devices and sensors to calculate the engine load and condition. With this information the ECU will adjust the ignition timing to provide optimal performance, driveability and emissions output.
If the self diagnostic circuit ("on board diagnostics") in the ECU detects a serious fault in the ignition system, it will activate the "CHECK ENGINE" light. By extracting the fault codes from the diagnostic socket, you can determine what component or components need further testing or replacement. The system can store up to three fault codes.
ECU INPUTS AND OUTPUTS
Input devices (the ECU receives):
^ Battery supply signal (voltage).
^ Ignition switch signal.
^ Crankshaft position and speed signal.
^ Knock signal.
^ Coolant temperature signal.
^ Air mass meter signal from fuel injection control unit.
^ Throttle position signal.
^ EGR temperature sensor signal (Calif. only).
Output devices (The ECU controls):
^ Power stage.
^ Crankshaft speed (RPM) signal to the fuel injection control unit (fuel injection ECU input device).
^ Crankshaft position signal to the fuel injection control unit (fuel injection ECU input device).
^ Knock signal to the fuel injection control unit (fuel injection ECU input device).
^ Diagnostic socket fault information.
^ EGR converter ground.
^ "CHECK ENGINE" light.
^ EGR converter (Calif. only).