Checking Fuel Pressure (Low Pressure) Using The Pressure Gauge

Toxic substances 

• Danger of poisoning or suffocation
• Danger of burns to the eyes and skin

→ Ventilate the work area well.

→ Never ingest or inhale.

→ Read specific information on the Hazard Sheet.

→ Do not smoke, eat or drink in the work area.

→ Avoid contact with hot parts or sources of ignition.

→ Use suction to remove ignitable vapours.

→ Attach warning sign in a clearly visible position.

1. Place a cloth under the fuel supply line (low-pressure) → Junction point for lines in engine compartment (3.6 l V6 naturally aspirated engine)  and open the line using two open-ended wrenches. Counter at the center piece while doing this and loosen the union nut at the engine side.

   → Fuel low-pressure line 

   Fig 1: Locating Junction Point Of Engine Compartment (3.6 L V6 Naturally Aspirated Engine)

   Courtesy of PORSCHE CARS NORTH AMERICA, INC.
   Fig 2: Locating Junction Point Of Engine Compartment (3.0 L V6 Biturbo Engine)

   Courtesy of PORSCHE CARS NORTH AMERICA, INC.
   Fig 3: Adjusting Fuel Low-Pressure Line

   Courtesy of PORSCHE CARS NORTH AMERICA, INC.
2. Checking fuel supply pressure (low-pressure) => 
   1. 2.1. Connect test equipment. The tool setup must be fitted with sealing rings (copper, aluminum, or plastic, etc.) between the individual components. The setup must be fully sealed. → Pressure measurement connection in vehicle (3.6 l V6 naturally aspirated engine) 
      1. Low-pressure line connection on engine side
      2. Low-pressure hose connection on body side
         Fig 4: Checking Fuel Supply Pressure (Low-Pressure)

         Courtesy of PORSCHE CARS NORTH AMERICA, INC.
   2. 2.2. Start the engine and leave it running at idle speed. Read off the fuel pressure on the pressure gauge. The pressure gauge pointer can oscillate slightly at idle speed. With increased idle speed (accelerator pressed slightly), the pointer deflection calms down. The fuel low-pressure system operates at a fuel pressure of 5.5 to 5.8 bar  . The pointer oscillates at around this value. Measurements under load (particularly on the turbo engine) can even generate values of below 5 bar (4.5 bar) briefly. This is not a sign of a defect.
   Fig 5: Checking Fuel Supply Pressure (3.0 L V6 Biturbo Engine)
   Courtesy of PORSCHE CARS NORTH AMERICA, INC.
3. Checking fuel retaining pressure (low-pressure) => 
   • Engine cold
   • Workshop air-conditioned to normal temperature
   • Fluctuations may occur if the engine is warm or if the outside temperature is high
   • Fully sealed measuring tool setup
   1. 3.1. Same tool setup and connection as for measuring the fuel delivery pressure (see above).
   2. 3.2. Allow engine to run for a few minutes. Switch off engine. Check the pressure drop. Drop in fuel pressure after "ignition is switched off" must not exceed 1 bar after 1 hour  . Make sure that the tool setup itself does not have any leaks (even the slightest leak). The fuel retaining pressure will decrease extremely rapidly and falsify the measured result with even the tiniest leak.