Fuel injection system characteristics (BMW 3 Series E21)

The 323i engine uses the K-Jetronic mechanical fuel injection system from Bosch.

The principle of operation of the fuel injection system

The fuel pump takes fuel from the fuel tank and delivers it to the accumulator in order to maintain the fuel pressure in the system within 1.5-2.4 kg/cm². The fuel is delivered under pressure through the filter to the fuel dispenser-distributor.

The air flow meter pressure disk, which is fixed on a movable lever and installed between the air filter and the throttle valve, deflects depending on the vacuum of the air in the engine. The displacement of the air flow meter pressure disk is transmitted to the distribution plunger of the fuel dispenser-distributor, thereby determining the amount of fuel supplied. The fuel quantity distributor, depending on the position of the air flow meter pressure disk, supplies the required amount of fuel to the engine cylinders through the injectors, ensuring the optimal composition of the fuel-air mixture. The fuel dispenser-distributor and the air flow meter form a mixture regulator.

Control pressure regulator (or a regulator of the working mixture composition when warming up the engine) reduces the pressure on the distributor plunger during engine warm-up. Reducing the control pressure with the same air flow leads to an increase in fuel supply and, consequently, to enrichment of the combustible mixture.

The additional air supply valve, installed in the air channel parallel to the throttle valve, supplies an additional amount of air to the engine during starting and warming up the engine, which leads to an increase in the engine crankshaft speed at idle.



To facilitate starting a cold engine, an electromagnetic starting nozzle is provided, the opening duration of which is regulated depending on the temperature of the coolant by a thermal time relay.

Data for adjustment

Fuel pressure in the system, kg/cm²: 4.5—5.2.

Control pressure on a warm engine or at idle, kg/cm²: 3.4–3.8.

Control pressure on cold engine: see graph.

Residual fuel pressure in the system after 20 minutes from engine stop, kg/cm², not less than: 1.5.

Idle speed, rpm: 850-950.

Content of carbon monoxide (CO) in exhaust gases, %: 1.0–2.0.

Fuel storage tank

Brand and type: Bosch 0 438 170 021.

Air flow meter

Brand and type: Bosch 0 438 120 086.
Color index: yellow-violet.

Fuel dispenser

Brand and type: Bosch 0 438 100 028.
Color index: black-red.

Mixture regulator

Brand and type: Bosch 0 438 060 025.

Fuel pump

Electric multi-section fuel pump.
Brand and type: Bosch 0 580 254 982.
Fuel supply pressure, kg/cm²: 5.
Pump capacity, l/h: 100.
Pump performance when tested on a vehicle with a 1/2 full fuel tank for 30 sec, cm³: 750.
Operating voltage, V: 7-15.
Current consumption. A, no more than: 4.7.

Injection nozzles

Brand and type: Bosch EP/LKE 6 0 437 502 006.
Injection start pressure, kg/cm²: 3.3.
Fuel spray cone angle: 35°.

Thermal time relay

Brand and type: Bosch 0 280 130 220.
Nominal voltage. V: 12.
Contact opening temperature,°C: +35.

Control pressure regulator

Brand and type: Bosch 0 438 140 005.
Nominal voltage, V: 12.
Maximum allowable voltage. V: 20.

Working voltage. V: 7-15.

Additional air supply valve

Brand and type: Bosch 0 280 140 118.


Nominal voltage, V: 12.
Operating voltage, V: 7-15.

Electromagnetic starting nozzle

Brand and type: Bosch 0 280 170 411.
Nominal voltage, V: 12.
Working voltage. V: 7-5.
Power consumption, W: 37.
Fuel spray cone angle: 80°.
Working pressure, kg/cm²: 4.5.