General Description, All Systems
LH System, General
The Bosch LH-Jetronic (Luftmassenmesser Hitzdraht) air mass meter with hot tilament sensor (mass air flow sensor) is a fuel injection system in which the best properties of different fuel injection systems are combined with mass air flow sensing, i.e. the density of the air is taken into account.
The LH-Jetronic system measures the air mass used by the engine, taking the composition of the air (temperature, pressure and humidity) into account as it flows through the mass air flow sensor.
This system gives an exact measure of the amount of oxygen supplied to the engine by the air mass and determines the amount of fuel needed for efficient combustion.
The system has the following advantages:
- Compensates for different temperature conditions.
- Adjusts the amount of fuel to the amount of oxygen in the air when driving at high altitudes.
- Few components.
- Low weight.
- Few moving parts.
- Good means of adapting the amount of fuel to actual needs (warm-up phase/acceleration phase).
There are tour versions of the LH-system: LH 2.2, 2.4, 2.4.1 and 2.4.2. The LH 2.2 and 2.4.2 versions are fitted to cars both with and without a catalytic converter while the LH 2.4 and 2.4.1 versions are fitted only to cars with a catalytic converter.
The most important differences between the different systems are that:
- the LH 2.4, which is a further development of the LH 2.2, has a control module with expanded memory capacity. This provides diagnostic capabilities.
- the diagnostic capability of the LH 2.4.1 is additionally expanded. The accuracy of the mass air flow sensor is also higher. Time delay of AC engagement is now obtained from the control module instead of from a relay as it was earlier.
- the fault diagnosis capability of the LH 2.4.2 system is expanded through design modifications to the control module. The throttle position switch has been replaced by a potentiometer. Idle speed control has been changed through an idle air control valve of new design.