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

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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.

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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.

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

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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.

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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
MPa = 10 bar = 10000 mbar

Connect the Tester and get it ready. > 9818 - PIWIS Tester II
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.

Call up the test value B070 Fuel high-pressure actual value.

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.

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

View of both PIWIS Tester values together (illustration for Panamera, German)

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).

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

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.