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 delivery pressure (low pressure) cannot be measured during a test drive. When you drive the vehicle, only the measured value Fuel high pressure actual value  can be read out with the PIWIS Tester in the DME control unit via the high-pressure sensor. There is no "low pressure" actual value.

Information 

The fuel system has a fuel pump, which is demand-controlled by a control unit, and two supply-driven sucking jet pumps.

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 pumps 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] => Panamera => [DME] => [Drive] link test/checks => [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] => [Panamera] => [DME] => [Actual] values/Input signals => [B070] Fuel high pressure actual value

   Fuel pressure is approx. 5500.0 hPa to 5800.0 hPa when the pump is running. 

   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).
   Fig 1: Display - PIWIS Tester Screen
   Courtesy of PORSCHE CARS NORTH AMERICA, INC.

   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 => 
   1. 3.1. Read out the fuel high pressure actual value  in the DME control unit using the PIWIS Tester.
      • 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.