BMW 7 Series: Notes Regarding The Fuel Pressure Test (Reference Pressure: Surrounding Area)

The characteristic of this version with ambient pressure:

The connection for the vacuum hose of the fuel pressure regulator is located between the throttle and the air cleaner or on the air cleaner.

Test prerequisite:

The correct fuel pressure regulator is fitted.

• Using the EPC, check whether the fuel pressure regulator suitable for the car is fitted: Connect test adapter.

The regulating function of the fuel pressure regulator must be ensured under all operating conditions. The fuel pump must always be able to generate a fuel pressure that is higher than the pressure that is adjusted by the pressure regulator.

The DME controls the injection period for which the injection rate is adjusted.

The fuel return line is depressurized at engine standstill and ignition key position 0.

The pressure regulator will close at engine standstill and ignition key position 0. The fuel pressure in the feed will be maintained for an extended period of time. A non-return valve will close in the fuel pump. This measure will maintain the fuel pressure in the fuel system. Extended start times are thereby prevented.

• Let the engine run at idle and measure the fuel pressure.

When the measured value is less than the nominal value - 0.2 bar:

• The line cross-sections in the fuel feed are constricted or the fuel filter is plugged, or
• The voltage supply to the fuel pump function is not OK: For example, as a result of high contact resistance (corrosion) in the plug connection between the wiring harness and the fuel pump.

When the measured value exceeds the nominal value + 0.2 bar:

• Stop the engine and then monitor the measured value.
• When the measured value drops to the nominal value, the line cross-sections in the fuel return line are constricted or plugged.
• Check the fuel lines for kinks.

  If no kinks are visible:

• Replace the return lines.

When the measured value remains too high, the pressure regulator is most likely faulty.

Attention:

There is a low probability that the return line is completely closed due to obstruction. Fuel would then leak out under pressure when the pressure regulator is removed!

• Have a cleaning rag ready and catch and dispose of escaping fuel.
• Do not replace the pressure regulator. Replace the return line instead.
• Let the engine run briefly at idle and then stop the engine.
• Write down the measured value at engine standstill.
• Read the measured value again after about 20 to 30 minutes at engine standstill.

The following check requires special tool 13 3 010 (hose clip).

If the measured value dropped by more than 0.5 bar:

• Start the engine and wait briefly for stable pressure build-up
• Stop the engine and immediately disconnect the feed line just before the pressure gauge with special tool 13 3 010
• Write down the measured value
• Read the measured value again after about 20 to 30 minutes at engine standstill

The following faults may be present if the measured value now dropped less than 0.5 bar:

• Fault in the feed lines
• Fault in the internal tank feed hose
• Faulty pressure-maintaining stop valve in the fuel pump

Check components. Replace faulty components.

If the measured value dropped again by more than 0.5 bar:

• Replace the pressure regulator.
• All fuel hoses and their hose clamps that were loosened during the checks must be replaced.
• Read out fault memory of DME control unit. Check stored fault messages. Rectify fault. Clear diagnostic fault entries from fault memory.

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