The principle of operation of the fuel injection system (BMW 3 Series E21)

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 1.7-2.4 kg/cm². 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, kg/cm²: 2.7-3.1.

Control pressure on a cold engine depending on the coolant temperature (see graph on page in the "Six-cylinder engine" section), kg/cm²: 0.5-2.0.

Residual fuel pressure in the system, kg/cm², not less than: 1.7.

Idle speed, rpm: 900±50.

Carbon monoxide (CO) content in exhaust gases, %:

• "318": 1,1;
• "320": 3,0.

Fine fuel filter

Brand: Purolator.

Type: "320i" until August 1987: GF 140/1; from September 1978 GF 140/1; "318i": GF 148.

Fuel storage tank

Make and type ("318i"): Bosch 0438 170 021.

Chamber volume, cm³ ("3201"): 20.

Working pressure, kg/cm²:

• "318i": 1,7-2.4;
• "320i": 5,0.

Mixture regulator

Brand and type:

• "318i": Bosch 0438 040 088;
• "320i": Bosch 0438 040 009.

Injection nozzles

Brands and type:

• "318i": Bosch 0437 502 006;
• "320i": Bosch 0437 502 007 EP/ LKE 7.

Injection start pressure, kg/cm²; 3,1;

Fuel spray cone angle ("320i"): 35°.

Electromagnetic starting nozzle

Brand and type:

• "318i" Bosch 0280 170 410;
• "320i": Bosch 0280 170 405.

Nominal voltage, V: 12.

Working pressure, kg/cm²:

• "318i": 4,5;
• "320i": approx. 4.5.

Operating voltage, V ("320i"): 7-15.

Power consumption, W ("320i"): 37.

Fuel spray cone angle ("320i"): 80°.

Thermal time relay

Brand and type: Bosch 0280 130 214.

Nominal voltage, V: 12.



Contact opening temperature, °C: +35.

Switch-on time, s, no more than: 8.

Control pressure regulator

Brand and type: Bosch 0438 140 005.

Nominal voltage, V: 12.

Maximum allowable voltage (short-term), A: 20.

Working voltage. V: 7-15.

Additional air supply valve

Brand and type:

• "318i": Bosch 0280 140 134;
• "320i": Bosch 0280 140 100.

Minimum voltage, V ("3201"): 12.

Maximum allowable voltage (short-term), In ("320"): 20.

Operating voltage, V ("3181"): 7-15.









(The original article is located on: «BMWMAN.ru»)