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 

• It is best to check the low-pressure area using both test methods (Tester and pressure gauge)  .

General information for converting pressure => 

• 10000 hPa = 10 bar = 10000 mbar
• 1000 kPa = 10 bar = 10000 mbar
• 1 MPa = 10 bar = 10, 000 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. 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 B220 Fuel low-pressure actual value.
3. 2.1. DME => Actual values/input signals => B220 Fuel low-pressure actual value

   The fuel low pressure (actual value) should be max. 0.5 bar below the required fuel pressure (setpoint value, B210 Fuel low-pressure setpoint value, FUP_EFP_SP)  .

4. Check the fuel system for leaks => 

   Information 

   The fuel holding pressure must only drop to max. half the stop pressure in one hour.

   1. 3.1. Read out the fuel low-pressure actual value  in the DME control unit using the PIWIS Tester.
      • The fuel holding pressure must only drop to max. half the stop pressure in one hour.
      • Compare with required pressure (DME --> Fuel low-pressure actual value/setpoint value "FUP_EFP_SP"). Monitor the fuel low pressure for about 5 to 10 minutes. Values of up to 0.5 bar  below the required pressure are permitted.
      • The pressure is not maintained. In other words: the fuel low-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 low-pressure actual value has only dropped slightly.