13 31... Notes on fuel pressure check (reference pressure: environment)

Feature 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 precondition: 

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 depressurised 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.

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

• Line cross-sections in fuel feed are constricted or fuel filter is clogged,

  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.

If the measured value is greater than the nominal value + 0.2 bar: 

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

If no kinks are visible:

• Replace return lines

If measured value remains too high, then pressure regulator is in all probability 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 has dropped by more than 0.5 bar: 

• Start engine and wait briefly for a stable pressure increase.
• Switch off the engine and immediately pinch off the delivery line just before the pressure gauge with the special tool 13 3 010.
• Note down measured value
• Read off measured value again after approx. 20 to 30 minutes while engine is stopped

If the measured value has now dropped by less than 0.5 bar, the following faults can be present: 

• Fault in delivery lines
• Fault in in-tank delivery hose
• Faulty pressure-holding non-return valve in fuel pump

Check components. Replace faulty components.

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

• Replace pressure regulator