Checking Fuel Pressure (Low Pressure) Using The PIWIS Tester (Quick Test)

Information 

• Faults in the fuel high-pressure injection system can also be caused by defects in the pre-delivery system (fuel low pressure)  .
• In the event of problems in the fuel high-pressure injection system, the pre-delivery system should be checked first  .

Information 

A leak in the fuel high-pressure pump supplying the engine (mechanical drive) dilutes the oil. Check the engine oil and initiate appropriate remedial action if necessary.

Information 

The fuel system contains a fuel pump, which is controlled according to demand by a control unit, and a supply-driven sucking jet pump.

Information 

If you suspect that a pump in the fuel tank is defective (particularly if symptoms include a very low fuel level), always check the sucking jet pump for dirt or blockages.

Information 

• Checking the low-pressure area with the high-pressure sensor cannot be used as the sole reference  .
• The high-pressure sensor has a certain percent inaccuracy in the low-pressure area  .
• It is best to check the low-pressure area using both test methods (Tester and pressure gauge)  .

General information on converting pressure → 

• 10000 hPa = 10 bar = 10000 mbar
• 1000 kPa = 10 bar = 10000 mbar
• 1 MPa = 10 bar = 10000 mbar

1. Connect the Tester and get it ready. PIWIS Tester II 9818 
   1. 1.1. Connect a charger to the vehicle battery. The voltage should be approx. 12.5 V (no rapid charging allowed because the voltage is too high!).
   2. 1.2. The fuel pump can be activated and deactivated as follows:
   3. 1.3. [Diagnostics] => [Cayenne] => [DME] => [Drive link test/Tests] => [Drive links] => [Fuel pump 1]
   4. 1.4. 100% is displayed. The fuel pump starts to deliver fuel when you press [Start].
   5. 1.5. The fuel pump stops when the percentage value changes to 0%. Press [Start] again.
2. Call up the test value [B070 Fuel high-pressure actual value].
   1. 2.1. [Diagnostics] → [Cayenne] → [DME] → [Actual values/input signals] → [B070 Fuel high-pressure actual value]

      Fuel pressure is about 5800.0 hPa to 6100.0 hPa when the pump is running  .

      Fig 1: PIWIS Tester Values Screen Display

      Courtesy of PORSCHE CARS NORTH AMERICA, INC.
      1. Drive links/tests
      2. Fuel pump status (0% when pump is off - 100% when pump is running). Always confirm by pressing [Start].
      3. Fuel pressure in hPa (figure shows holding pressure shortly after switching pump off).

      Information 

      The fuel holding pressure must only drop by max. 1 bar (1000 mbar) in one hour.

3. Step 2: Check the fuel system for leaks (check holding pressure) → 
   1. 3.1. Read out the fuel high-pressure actual value  in the DME control unit using the PIWIS Tester.
      • Switch on ignition, activate fuel pump briefly, then switch off the fuel pump.
      • Nominal pressure is approx. 5000 to 5500.0 hPa. Monitor the fuel pressure for about 5 to 10 minutes.
      • The pressure is not  maintained. In other words: the fuel high-pressure actual value  has dropped considerably. There is an internal or external leak in the fuel system.
      • The pressure is maintained. In other words: the fuel high-pressure actual value  has only dropped slightly.