LH-Jetronic System Components
FUEL FEED PUMP (TANK PUMP).
Electrically operated vane pump, completely immersed in the gasoline in the fuel tank. It feeds fuel to the (main) fuel pump via a mesh screen and a check valve.
FUEL PUMP.
Fuel pump and fuel filter are attached to a bracket underneath the car, under left rear seat.
Electrically operated roller pump. Equipped with check valve and overpressure relief valve, which opens in case the system (particularly the fuel filter) becomes clogged and fuel pressure rises too high.
FUEL FILTER.
Fuel pump and fuel filter are attached to a bracket underneath the car, under left rear seat.
Has a paper element with a very small pore size and a mesh to trap any particles that may fall away from the paper element. The complete filter unit is discarded when replaced.
INJECTORS.
Located on the intake manifold and connected by the injection manifold, which has connectors for the line pressure regulator and the cold start injector.
The injectors are solenoid-operated valves. The electronic Control Unit controls the duration of the injection time.
LINE PRESSURE REGULATOR.
Maintains a fuel pressure of 43.5 psi (early production vehicles: 35 psi) above intake manifold pressure. Excess fuel is bled off to the fuel tank via a return line.
Fuel Pressure
Volvo P/N: 1306935, Bosch P/N: 0 280 160 214 - 35.0 psi
Volvo P/N: 1306965, Bosch P/N: 0 280 160 213 - 43.5 psi
COLD START INJECTOR.
Supplies extra fuel to the engine and is controlled by the thermal time switch. The cold start injector is a solenoid operated valve and operates when the starter is energized.
THERMAL TIME SWITCH.
Controls current to the cold start injector and is influenced by engine coolant temperature. It causes termination of cold start fuel injection at engine temperatures above 35°C (95°F) (early production vehicles: 15°C (60°F)). A heating coil, acting on a bimetal strip, provides for maximum injection time at low temperatures. Injection time decreases at higher temperatures.
The thermal time switch and cold start injector only operate while the starter motor is switched on.
VACUUM SWITCH.
"Used to indicate full load/idle (low ported vacuum) and part load conditions (maximum vacuum)."
ENGINE SPEED AND INJECTION TIMING.
Engine speed pulses are tapped from the low tension side of the ignition coil. Provide both engine speed and injection timing information to the Electronic Control Unit.
COOLANT TEMPERATURE SENSOR.
Is screwed into the cylinder head. As the engine coolant temperature increases, the resistance in the sensor falls, giving an analog temperature signal to the Electronic Control Unit.
Coolant Temperature Resistance Graph:
The graph shows how coolant temperature sensor resistance changes with temperature.
Below are three test point values, taken from the graph:
Values for certain temperatures:
80°C (175°F) 270-390 ohms.
20°C (68°F) 2,100-2,900 ohms.
-10°C (14°F) 7,000-11,600 ohms.
OXYGEN SENSOR (LAMBDA-SOND).
It measures the oxygen level in the exhaust gases and provides an electrical signal to the Electronic Control Unit.
Is located in the exhaust manifold.
FUEL PUMP RELAY.
Energizes the fuel feed pump (tank pump) via a separate fuse, and the main fuel pump.
SYSTEM RELAY.
Provides current to the Electronic Control Unit. It is energized during filament dirt burn-off after the ignition has been switched off.
AIR MASS METER.
Is unique to the LH-Jetronic system. It measures air flow by mass (CI fuel injection system measures by volume). The basic sensing information is provided by a heated platinum wire.
When engine is stopped, dirt build-up on the platinum wire filament is burned off electrically by raising the filament temperature to 1050°C for less than one second.
CO adjustment is accomplished by a screw on the air mass meter. The screw is connected by a spring to a linear potentiometer of 1000 ohms. The potentiometer is located on the circuit board inside the air mass meter. It has a range of 15 turns and lacks distinct end stops. The potentiometer adds a voltage to the output signal from the air mass meter. The amount of fuel injected can be changed by 40%. Zero ohms on the potentiometer, measured across terminals 6 and 12, provides maximum lean condition. Turning the screw counter-clockwise makes the idle mixture richer.
Idle CO should be 0.6% (0.4-0.8% permitted) with the oxygen sensor disconnected.
When delivered from factory, the CO adjustment screw is sealed by an aluminium plug with a hardened steel insert.
ELECTRONIC CONTROL UNIT (ECU).
It is the brain of the system. It receives and evaluates readings from the various sensors. It includes a microprocessor which calculates the correct amount of fuel to be injected. The micro-processor is programmed to take account of all possible variations in engine conditions and to produce a control signal to the injectors.
Removing Connector On Electronic Control Unit
Press lock tab UP, then FOLD out connector upper part. DO NOT pull straight out.
ELECTRONIC CONTROL UNIT CONNECTOR TERMINALS
KEY TO TERMINALS.
1. Input, engine speed from terminal 1 on ignition coil.
3. Input, from vacuum switch.
4. Input, from terminal 50 on starter motor.
5. Ground, for electronics in Electronic Control Unit.
6. Ground, for electronics in air mass meter.
7. Input, from air mass meter.
8. Control signal, filament burn-off.
9. Output, current to air mass meter.
10. Input, current from system relay.
11. Injector test.
12. Input, CO setting.
13. Input, from coolant temperature sensor.
14. Output, control current to injectors 3+4.
15. Output, control current to injectors 1+2.
16. Ground, for electronics in Electronic Control Unit.
17. Ground, for electronics in Electronic Control Unit.
19. Shield for wire to terminal ion ignition coil.
20. Input, ignition ON, from terminal 15 on ignition coil, or terminal 1 on AC relay.
22. Output, to LH-Jetronic system testing pick-up point.
23. Shield for wire to oxygen sensor.
24. Input, from oxygen sensor.
28. Output, control ground for fuel pump relay.
34. Output, control ground for system relay.