Fuel Pressure Regulator

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As operating mode of engine varies, so does amount of fuel it requires, ranging from low at idle speed to high at full throttle. This requirement is set with the help of pressure regulator. Pressure regulator governs fuel pressure, controlling it between low and high to suit requirements. Fine adjustment of fuel injection quantity is performed using fuel injection period controlled by DME. Vacuum in intake manifold provides load connection for pressure regulation. This vacuum is applied to diaphragm in pressure regulator. At idle speed or when coasting, a vacuum develops in intake pipe. Fuel pressure reduces by this amount, starting from nominal value. Nominal value is embossed in housing of pressure regulator. At full throttle, intake pipe is approximately zero and pressure regulator controls fuel pressure to nominal value embossed on housing.

Remove fuel pressure regulator. Note code number and nominal pressure on fuel pressure regulator body. Install BMW Service Tester (133060) with Connecting Hose (133064) in fuel feed left line.
Remove fuel pump relay. See RELAY LOCATION table. Connect jumper wire between relay base terminals No. 30 and 87. Read off fuel injection pressure on pressure gauge.
If fuel pressure drops rapidly, seal return line (upper line) with Clamp (133010) and briefly operate fuel pump. If injection pressure in now stable, pressure regulator is defective. If injection pressure drops, check for leak in front of pressure regulator.