LH Fuel System
LH fuel system 2.4: I16 Lambda, 1988Operation
Sixteen-valve engines with Lambda are equipped with version 2.4 of the Bosch LH Jetronic fuel injection system, which is an update of version 2.2. LH is an abbreviation of Luftmassenmesser Hitzdraht (Air mass meter with hot filament). The fuel injection system is controlled and monitored by control unit 200, which includes a microprocessor.
A number of new features have been introduced, such as:
^ Adaptive Lambda control system
^ AIC (Automatic Idle Control) valve with built-in "limp-home" function. When necessary, the valve provides a high, fixed idling speed of 1200 rlmin.
^ Adaptive idle control system. Normal changes are compensated for automatically. The idling speed is controlled by means of valve 272.
^ Built-in deceleration function. During overrun braking, it cuts off the fuel supply within certain engine speed ranges.
^ A new, electrically-operated relief valve (321) for the charcoal canister. Controlled by signals from the control unit. The charcoal in the canister absorbs fuel fumes in the vent line from the tank.
^ Built-in fault diagnosis system. Gives fault codes via the CHECK ENGINE lamp.
The system receives a positive supply from fuse 22 when the ignition switch is in the start or drive position, and a constant supply from +30 to relays 229 and 102.
On the basis of the data stored in the control unit and the incoming information from various sensors, the control unit calculates and controls the opening times of the electrically operated fuel injection valves (206). Control unit 200 receives information on the engine speed by sensing the pulses from the ignition system.
Throttle valve angle transmitter 203 provides information to the control unit on the throttle angle. The transmitter has two contact positions, i.e. 0~ (idling speed) and 720 throttle angle.
Temperature transmitter 202 is of Negative Temperature Coefficient (NTC) type and provides continuous information to the control unit on the engine temperature. In the event of loss of this signal, the control unit will simulate, by default, an engine temperature of +45 °C.
Air mass meter 205 is built into a plastic housing. In the event of a loss of signal from the air mass meter, e.g. if the filament should fail, an emergency system known as the "Limp-home" function in the control unit will come into operation. The car can then be driven, although its driveability will be limited. When the "Limp-home" function is operative, warning lamp 47P, CHECK ENGINE, will light up. It is located in the combined instrument, and is supplied from fuse 7. (The lamp can also be energised from EZK-type ignition systems.)
The engine is supplied with fuel by electrically driven fuel pump 103 and feed pump 101 drawing fuel from the fuel tank and building up a pressure in the fuel system.
The control unit is connected to the air-conditioning system via pin 16, "AC 156". When the AC compressor is running, the control unit will compensate for the increased load applied by the compressor at engine idling speed. A signal (earth) is applied from pin 3 at full throttle, which disconnects the AC compressor.
Test connector 204 should be used for all fault tracing. When pin 2 in the socket is earthed, flashing codes will be obtained on the CHECK ENGINE lamp.
Exhaust gas emission control, Lambda
The car is equipped with an adaptive 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 to X = I as possible. The sensor is heated by preheater 271 (protected by fuse 285 in the wiring).
Automatic transmission
Cars with automatic transmission are also equipped with switch 76 which will close when the selector lever is set to "Drive", and the control unit will then compensate for the increased load applied by the automatic transmission when the engine is running at idling speed.
Fault-tracing hints
When fault-tracing in the wiring for the fuel system, always observe the following:
1. Always disconnect the 35-pole connector on the control unit and the connector on the air mass meter. N.B. These two components can easily be seriously damaged if measurements are carried out on their terminal pins.
2. Always disconnect the connection to the suspected component.
3. Use an ohmmeter - not a buzzer - for checking the wiring.
Before checking the wiring, always start by checking fuse 22 and checking that the supply to it is live. Also check fuse 7 and the fuse in the wiring for the Lambda sensor preheater.
Earthing point 201 on the engine lifting lug is important for correct operation of the fuel system. If the location of the earthing point is altered, such as when other work is being carried out on the engine, the performance of the system may be disturbed.