Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSSAAB1993900 L4-2118CC 2.1L DOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSDESCRIPTION AND OPERATIONLH SYSTEMGENERAL OVERVIEW
1993 Saab 900 L4-2118cc 2.1L DOHC
General Overview
1993 Saab 900 L4-2118cc 2.1L DOHCSECTION General Overview
LH fuel injection system
General
The Bosch LH-Jetronic Luftmassenmesser Hitzdraht) fuel injection system, comprising a mass air flow sensor incorporating a filament (hot-wire sensor), combines the best features of different fuel injection systems with measurement of the air mass, i.e. the density of the induction air is taken into account - unlike earlier fuel injection systems.
In the LH-Jetronic system, the air mass consumed by the engine is measured, which means that allowance is made for the composition of the air (temperature, pressure and humidity). Measurement of the air mass is performed by the mass air flow sensor with the hot- wire sensor, which measure the air upstream of the inlet manifold.
This method provides a more exact measure of the quantity of oxygen supplied to the engine by the air mass, which determines the quantity of fuel required for efficient combustion.
In all previous fuel injection systems, only the air volume (quantity of air) and/or the atmospheric pressure has been taken into account.
The LH system has the following advantages over earlier types of fuel injection:
- Compensation for temperature variations.
- Adjusts the quantity of fuel to the quantity of oxygen at high altitudes.
- Fewer components.
- Lighter.
- Fewer moving parts.
- Wider scope for adapting the quantity of fuel to actual needs (warm-up period/acceleration phase).
General
The Bosch LH-Jetronic Luftmassenmesser Hitzdraht) fuel injection system, comprising a mass air flow sensor incorporating a filament (hot-wire sensor), combines the best features of different fuel injection systems with measurement of the air mass, i.e. the density of the induction air is taken into account - unlike earlier fuel injection systems.
In the LH-Jetronic system, the air mass consumed by the engine is measured, which means that allowance is made for the composition of the air (temperature, pressure and humidity). Measurement of the air mass is performed by the mass air flow sensor with the hot- wire sensor, which measure the air upstream of the inlet manifold.
This method provides a more exact measure of the quantity of oxygen supplied to the engine by the air mass, which determines the quantity of fuel required for efficient combustion.
In all previous fuel injection systems, only the air volume (quantity of air) and/or the atmospheric pressure has been taken into account.
The LH system has the following advantages over earlier types of fuel injection:
- Compensation for temperature variations.
- Adjusts the quantity of fuel to the quantity of oxygen at high altitudes.
- Fewer components.
- Lighter.
- Fewer moving parts.
- Wider scope for adapting the quantity of fuel to actual needs (warm-up period/acceleration phase).
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.