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Checking Fuel Pressure (Low Pressure)

WARNING: This page is about a different car, the 2010 Porsche Cayenne, 2009 Porsche Cayenne, and 2008 Porsche Cayenne. However, it is still accessible from the selected car via links, so may be relevant.
  1. Checking fuel supply pressure (low pressure) => 
    1. 1.1. Connect pressure gauge with stopcock tester K-Jetronic Tester V.A.G. 1318 WE 1291  using adapter 1318/7 and connecting line connection line 9705/3  ("female" rapid-action coupling) on the side of the stopcock. On the other side of the stopcock, connect adapter 1318/15 (one-piece connecting piece) and connecting line connection line 9705/3  ("male" rapid-action coupling). The tool setup must be fitted with sealing rings (copper, aluminium, plastic, etc.) between the individual components. The setup must be fully sealed.
      Fig 1: Identifying Tool For Fuel Delivery Pressure
      G09409777Courtesy of PORSCHE CARS NORTH AMERICA, INC.
      1. Connecting line connection line 9705/3  ("male" rapid-action coupling) => used for checking the fuel delivery pressure.
      2. Adapter 1318/15 (one-piece connecting piece); accessory for K-Jetronic Tester V.A.G. 1318 WE 1291;  => used for checking the fuel delivery pressure.
      3. Pressure gauge with stopcock tester K-Jetronic Tester V.A.G. 1318 WE 1291 
      4. Adapter 1318/7 from K-Jetronic Tester V.A.G. 1318 WE 1291 
      5. Connecting line connection line 9705/3  ("female" rapid-action coupling)
    2. 1.2. Connect measuring tool -2-  between the connection unit output -3-  and the fuel supply line -1-  . The stopcock is set to flow.
      Fig 2: Connecting Measuring Tool Between Connection Unit Output And Fuel Supply Line
      G09409778Courtesy of PORSCHE CARS NORTH AMERICA, INC.
    3. 1.3. Start the engine and allow it to run at idle speed. Read the fuel pressure on the pressure gauge. The pointer on the pressure gauge may oscillate when idling (due to the high-pressure pump switching between pressure stage and intake stage). With increased idle speed (accelerator pressed slightly), the pointer deflection calms down. The fuel low-pressure system operates at a constant pressure of 5.5 bar  . The pointer oscillates at around this value. A measurement performed while driving by a second person can also generate values of below 5 bar (4.5 bar) briefly at full throttle (with turbo in particular). This is not a sign of a defect.
    4. 1.4. Alternatively, each individual fuel pump in the tank can also be actuated using the adapter 9479 instead of the fuel pump relay. For assignment of fuel pump relays - see wiring diagram. Each individual fuel pump generates a constant pressure of 5.5 bar. 
  2. Checking fuel retaining pressure (low pressure) => 
    • Engine cold
    • Workshop air-conditioned to normal temperature
    • Fluctuations may occur if the engine is warm or the outside temperature is high
    • Fully sealed measuring tool setup
    1. 2.1. Same tool setup and connection as for measuring the fuel delivery pressure (see above).
    2. 2.2. 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.
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