Checking the operation and replacing the fuel pressure regulator (BMW 5 Series E28)

Fuel is extremely flammable, so take extra precautions when working on any part of the fuel system. Do not smoke or allow open flames or unshaded lamps near the work area. Do not work in a garage where natural gas equipment is installed (such as water heaters or clothes dryers) with a wick. If fuel gets on your skin, wash it off immediately with soap and water. When working on the fuel system, wear safety glasses and keep a fire extinguisher handy.

If your vehicle's radio is equipped with an anti-theft system, make sure you know the correct activation code before disconnecting the battery. Before disconnecting the wire, refer to Section Anti-theft audio system and instrument cluster language.

If a message in another language appears on the instrument panel display after connecting the battery, refer to Section 1 for the language setting procedure Anti-theft audio system and instrument cluster language.

Examination

1. Relieve the pressure in the fuel system (see section Relieving pressure in the fuel injection system).

2. Disconnect the negative battery cable.

3. Disconnect the fuel line and connect a fuel pressure gauge (see section Checking fuel pressure/fuel pump). Connect the battery.

4. Create pressure in the fuel system (install the fuel pump fuse and turn on the ignition) and check the meter connections for leaks.

5. Connect a vacuum pump to the fuel pressure regulator.



6. Turn on the fuel pump (see section Checking fuel pressure/fuel pump). Read the fuel pressure gauge readings with and without vacuum applied to the pressure regulator. The fuel pressure should decrease as the vacuum increases.



7. Turn off the fuel pump and connect a vacuum hose to the regulator. Start the engine and check the fuel pressure at idle, comparing it with the value given in Table of sizes and adjustment data at the end of the manual. Disconnect the vacuum hose and watch the gauge - when you disconnect the hose, the pressure should suddenly increase to the maximum.

8. If the fuel pressure is low, close the fuel return line and monitor the pressure. If the pressure does not increase, the fuel pump is faulty or the fuel line is clogged. If the pressure does not increase abruptly, replace the pressure regulator.

9. If the measured fuel pressure is very high, stop the engine, disconnect the fuel return line and blow through it to check for blockage. If the line is not blocked, replace the fuel pressure regulator.

10. If the pressure value does not change as described in item 7, connect a vacuum gauge to the vacuum hose of the pressure regulator and measure the vacuum (the engine is idling).

11. If vacuum is present, replace the fuel pressure regulator.

12. If the meter does not register a vacuum, check for a leak or blockage in the hose and inlet.

Replacement

1. Relieve the pressure in the fuel system (see section Relieving pressure in the fuel injection system).

2. Disconnect the negative battery cable.

If your vehicle's radio has an anti-theft system, make sure you know the correct activation code before disconnecting the battery. Before disconnecting the wire, refer to Section Anti-theft audio system and instrument cluster language.

If a message in another language appears on the instrument cluster display after connecting the battery, refer to Section 1 for the language setting procedure Anti-theft audio system and instrument cluster language.



3. Disconnect the vacuum hose and fuel return hose from the pressure regulator, then unscrew the mounting bolts (shown by arrows).

4. Remove the pressure regulator.

5. Installation is the reverse of removal. Make sure to install a new O-ring. Apply a thin coat of engine oil to the ring before installation.

6. After installing the pressure regulator, check for fuel leaks.