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    Thread: Low fuel pressure at injectors, but pressure seems fine at pump

    1. Junior Member
      Join Date
      May 3rd, 2012
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      Portland, Oregon
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      1997 Jetta GLX VR6
      10-07-2012 06:40 PM #1
      I have a 1997 Jetta GLX with the 12v VR6. When I measure the fuel pressure at the injector rail I see 34 PSI, which rises to 44 PSI when I disconnect the vacuum line to the fuel pressure regulator. I tested fuel pressure at the fuel pump and find 96 PSI. I removed the (original equipment) fuel filter and found it to be pretty restricted (very scientifically -- I tried to blow through it) so I replaced it with a new one. This made no difference at all to my fuel pressure measurements -- I'm still seeing 34 PSI at the injectors when the Bentley says I should see 51 PSI at idle.

      Is 96 PSI a good reading at the fuel pump?

      What else might be plugged/kinked between the fuel filter and the injector rail? I don't see any issues with the fuel hoses.

    2. Member
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      Apr 5th, 2006
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      NJ
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      10-07-2012 08:34 PM #2
      maybe the regulator isnt regulating...

    3. Global CSI Moderator nater's Avatar
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      2008 Passat 4Mo 3.6L Wagon, 98 VRt, 2010 Routan/Caravan :)
      10-08-2012 09:05 AM #3
      You have the Bentley...what does it say your fuel pump should pump at?

    4. Junior Member
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      May 3rd, 2012
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      Portland, Oregon
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      1997 Jetta GLX VR6
      10-13-2012 06:38 PM #4
      I don't see a spec in the Bentley about pressure at the pump. However, I did just run the fuel delivery test and found just under 700ml fuel delivered in 30 seconds, with 10.9v across the pump terminals while running.

      The book's graph says to expect 725-845 ml at 10.9v

      I think I need a new pump :-(

    5. Junior Member
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      May 3rd, 2012
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      Portland, Oregon
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      1997 Jetta GLX VR6
      10-13-2012 06:50 PM #5
      I thought it might be the FPR too, but the readings are unchanged with the new FPR in place.

    6. Junior Member
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      May 3rd, 2012
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      Portland, Oregon
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      1997 Jetta GLX VR6
      10-18-2012 12:54 PM #6
      I have been working slowly at this over the last several weeks. I have:
      - found fuel pressure at the injector rail to be ~34 psi rather than 51 psi the Bentley recommends
      - replaced the fuel pressure regulator; no change in fuel pressure as measured at the injector rail
      - replaced my 15 year old fuel filter (no change in fuel pressure resulted)
      - measured fuel flow rate over 30 seconds; I found just less than 700ml when the Bentley calls for at least 725ml.
      - replaced fuel pump, again with no change in fuel pressure

      The fuel pump creates a static pressure of almost 100 PSI when I route the pump output directly to the pressure gauge, so I know the pump generates lots of pressure. The fact that the pressure is low at the injector rail leads me to think the fuel is leaking out of the supply lines either to the ambient, into the engine, or into the return line to the tank. I don't think it's leaking to the outside since I have no fuel smell or visible leaks.

      Can the injectors leak in some fashion that would allow enough fuel to escape to let the injector rail pressure fall ~17 psi?

      Has anyone seen a way in which fuel could leak around/past the fuel pressure regulator into the fuel return line?

      I'm having trouble thinking of where the fuel could be going.

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