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The LH Jetronic is an advancement on the L and LE systems. It uses a hot wire air mass meter which measures the air inducted into the engine. This measurement is independent of the air density which is itself dependent upon temperature and pressure. I have not worked on an LH system but this system is very similar to the ECCS in that they both utilise the hot wire air mass sensor.

1:  Fuel Pump 6:  Engine Temp Sensor
2:  Fuel Filter 7:  Auxilary air valve
3:  Fuel Pressure Regulator 8:  Throttle Position Switch (TPS)
4:  Injector 9:  Oxygen Sensor
5:  Hot Wire Air Mass Sensor 10. ECU

(1) Fuel Pump:

 

The electric Fuel Pump and filter are located at the rear of the car, external to the fuel tank. The pump operates for a few seconds whenever the ignition is switched on. This allows fuel pressure to build up before the engine is cranked. It operates continuously when the motor is cranking or running. The fuel pump supplies fuel several times more than the required pressure to the Fuel Pressure Regulator.
(2) Fuel Filter:

 

Read fuel filter section.

(3) Fuel Pressure Regulator:

 

The Fuel Pressure Regulator, maintains the injector supply pressure in the fuel rail at 2.5 Bar (approx 37psi) and in this system not adjustable. It maintains the pressure in the fuel rail by restricting the amount of fuel returned to the tank. Manifold vacuum is applied to the regulator and when the vacuum drops as in acceleration, the fuel pressure will raise approx .5 Bar.

(4) Injector:

 

The entry point of fuel into the intake manifold. There is one injector per cylinder and they are electro-magnetically activated. The time they are activated is measured in m/s (milliseconds). The injector is designed to spray fuel into the manifold in an atomized state so that the fuel mixes effectively with the incoming air.

(5) Hot Wire Air Mass Sensor:

 

 

(6) Engine Temp Sensor:

 

The coolant sensor when cold, tells the ECU to richen the mixture. As the engine warms up the sensor tells the ECU to progressively return injection duration to normal as it reaches operating temperature.

(7) Auxilary Air Valve:

 

A cold motor needs to idle slightly faster requiring a little additional air and fuel. This system uses an Auxiliary Air Valve, which allows a small amount of air to bypass the throttle butterfly when cold, gradually reducing the amount as the coolant warms up. This is the same as holding the throttle slightly open. The ECU automatically supplies the matching fuel as dictated by the Air Mass meter and coolant temperature sensor.

(8) Throttle Position Switch: (TPS)

 
 

(9) Oxygen Sensor:

 

read oxygen sensor section

(10) ECU:

 

The ECU determines how much fuel is needed and controls how long the injectors are held open during each piston stroke. The ECU will vary this duration in accordance with inputs from the following sensors:

  1. The main input is the Hot Wire Air Mass Sensor which measures airflow by the cooling effect on the hot wire as air flows throught the sensor.
  2. Throttle position and relative movement of the throttle from the Throttle Position Switch (TPS), which is connected to the butterfly shaft.
  3. Coolant temperature from a Temperature Sensor, which is generally fitted in the cylinder head near the thermostat housing.
  4. Oxygen Sensor which measures excess air in the exhaust.