LH Fuel System
LH 2.4.2 fuel system: I16Operation
The LH 2.4.2 fuel injection system is controlled and monitored by control unit 200.
The system controls the opening times of the injection valves, thus supplying the engine with the optimum quantity of fuel for combustion in any situation. For this purpose, the electronic control unit employs incoming information on a number of parameters, such as the air flow (engine load), engine temperature, road speed, engine speed and the oxygen content in the exhaust gases.
The features of the LH 2.4.2 system are as follows:
^ Adaptive (self-instructive) Lambda control system.
^ Adaptive idling control system with built-in "limp-home" system. If a fault should occur, AIC valve 272 will run the engine at a fixed idling speed of 1200 r/min.
^ Built-in deceleration function which will interrupt the fuel supply during overrun braking within a certain engine speed range.
^ Electrically operated vent valve 321 for the charcoal canister of the fuel vent system.
^ Shift-up indication (US, CA).
^ Connection of the AC, controlled by control unit 200.
^ Built-in fault diagnosis system. Provides flashing fault codes on the CHECK ENGINE lamp or can be read by means of the ISAT.
Power supply
The system receives its positive supply from fuse 22 when the ignition switch is in the start or drive position, and a constant +30 supply to relays 229 and 102.
Signals to the control unit
The system calculates and controls the opening times of the injection valves on the basis of the data stored in the control unit and incoming information received from various transmitters.
The control unit receives information on the engine speed from the ignition system.
Throttle angle transmitter 203 provides information on the throttle angle. The potentiometer gives information continuously at angles from 0~ (idling) to 720 (full throttle).
Temperature transmitter 202 of Negative Temperature Coefficient (NTC) type provides the control unit with information on the engine coolant temperature. If the signal is lost, the control unit will simulate an engine temperature of 45 °C.
Air mass meter 205 is built into a plastic housing and has no CO adjusting screw. In the event of loss of signal from the air mass meter, e.g. if the filament should fail, a "Limp-home" function will come into operation and will enable the car to be driven, although with limited driveability.
CHECK ENGINE lamp 47P in the combined instrument will light up when the Limp-home function is in operation or if some other serious fault should occur in the injection system.
Modulating valve 390 controls the control pressure to the EGR valve. The open/closed modulation ratio of the valve is determined on the basis of the engine load, speed and temperature at any given time. The open/closed ratio determines the value of the control pressure which, in turn, controls the EGR valve.
Fuel supply
Fuel is supplied to the engine by fuel pump 323 which draws fuel from the tank and pressurises it in the system.
Air Conditioning (AC) and Automatic Climate Control (ACC) systems
Cable 405 connected to pin 14 of the control unit provides the fuel system with information on whether the AC system is in operation. Pin 11 of the control unit then earths pin 85 of AC relay 156. When the AC compressor is running, the control unit will compensate for the increased load caused by the compressor at engine idling speed.
At full throttle, the earth circuit to the AC relay via pin 11 on the control unit is opened, which disconnects the AC compressor.
Test connector
Test connector 204 is used for fault tracing. By connecting pin 2 of the test connector to earth, any fault codes stored can be read from the flashing of the CHECK ENGINE lamp.
Lambda exhaust emission control
The system is connected to an adaptive (self-instructive) Lambda system which compensates for variations in the fuel/air mixture caused by changes in the fuel system. Lambda sensor 136 continually measures the oxygen content of the exhaust gases, thus enabling the control unit to adjust the mixture to as close as possible Lambda = 1. The sensor is heated by preheater 271, protected by fuse 1.
Cars with automatic transmission
When the selector lever is in one of the drive positions, switch 76 will close, and the control unit will then compensate for the increased load applied by the automatic transmission.
Shift-up Indication
Shift-up indication is provided on cars with manual gearbox, destined for the USA and Canada.
The system helps the driver utilise the engine characteristics in the best possible way, thus minimising the fuel consumption. This indication is provided by lamp 47K in the combined instrument lighting up when the engine speed and throttle setting are such that the driver should shift up to a higher gear.
When the engine load is below a certain value (basic injection time) and the engine speed has reached a certain value, the control unit will earth lamp 47K via pin 26. The engine speeds at which the lamp lights up are dependent on the gear which is engaged, as follows:
1st 2000 r/min These values are approximate
2nd 1900 r/min and may vary with the variant
3rd 1850 r/min of the car and the model year.
4th 1775 r/min
The control unit determines the gear which is engaged on the basis of information received from speed transmitter 132 and the engine speed.
The lamp will also light up, regardless of the load, if the engine speed is above 5000 rim in when 1st, 2nd, 3rd or 4th gear is engaged.
To avoid incorrect indications, the system is inoperative under the following conditions:
^ when the signal from engine temperature transmitter 202 is below its value at normal operating temperature of the engine
^ at idling speed, when throttle angle transmitter 203 is in the idling position
^ when 5th gear is engaged
In addition, all input signals must have been recorded for at least approximately I second.
Fault tracing hints
Note: Activate and read any fault codes before disconnecting the connector from the control unit, since the contents of the memory will otherwise be erased as soon as the connector is disconnected.
1. Check fuse 22 and check that the supply to it is live. Also check fuse 1 for the Lambda sensor preheater.
Caution: Never disconnect the control unit connector when the control unit is live. After the ignition has been switched off, it takes about 30 seconds for the main relay to trip. So always wait at least 40 seconds before disconnecting the control unit connector.
2. Disconnect the 35-pole connector from the control unit and the connector from the air mass meter. Take all readings at the rear of the connectors, since taking readings directly at the terminal pins may cause contact problems and maloperation. Corrosion in the connectors may give rise to maloperation. Check and clean as necessary.
3. Disconnect the electrical connections from components which are suspected of being faulty.
4. Use a universal meter or the ISAT - not a buzzer - to carry out check measurements in the wiring.
Note: The common earthing point G7 of the system is important for the correct operation of the system. Do not change the location of this earthing point or the connections to it.