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    Thread: what is 3bar psi at idle??

    1. Member mveitenheimer's Avatar
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      04-05-2008 12:32 AM #1
      what does the 3bar FPR while idling? shouldent it be 43 psi? i have a adjustable FPR and i cant get my fueling tuned rite
      am i off somewhere here.ive got it set to 40 psi at idle is this wrong?
      Quote Originally Posted by macleanshaun View Post
      Imagine a really fat girl putting on a big belt around her stomach, but tightening it WAY too tight. Her stomach will push both up and down out of the belt.
      haha

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      04-05-2008 01:50 AM #2
      Your FPR just keeps a set pressure difference between the fuel in the fuel rail, and the intake manifold pressure/vacuum. Constant pressure difference across the fuel injectors means that you can accurately control the fuel with the ECU.

      So basically, your fuel pressure will only be 3 bar when the absolute pressure in your intake manifold is 1 bar (zero boost, wide open throttle in a n/a car). Average manifold vacuum at idle with stock cam(s) is 15"Hg, which is 0.5 bar vacuum. 3 bar FPR + (-0.5 bar manifold) = 2.5 bar referenced to atmosphere = 36.x psi.

      If you've got a vacuum section on your boost gauge (if you've got one), what does it read?


    3. Member mveitenheimer's Avatar
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      04-05-2008 11:21 AM #3
      20 hg but I also have a 270 cam


      Modified by mveitenheimer at 11:51 AM 4-5-2008
      Quote Originally Posted by macleanshaun View Post
      Imagine a really fat girl putting on a big belt around her stomach, but tightening it WAY too tight. Her stomach will push both up and down out of the belt.
      haha

    4. Member mveitenheimer's Avatar
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      04-05-2008 10:15 PM #4
      Quote, originally posted by 84_GLI_coupe »
      Your FPR just keeps a set pressure difference between the fuel in the fuel rail, and the intake manifold pressure/vacuum. Constant pressure difference across the fuel injectors means that you can accurately control the fuel with the ECU.

      So basically, your fuel pressure will only be 3 bar when the absolute pressure in your intake manifold is 1 bar (zero boost, wide open throttle in a n/a car). Average manifold vacuum at idle with stock cam(s) is 15"Hg, which is 0.5 bar vacuum. 3 bar FPR + (-0.5 bar manifold) = 2.5 bar referenced to atmosphere = 36.x psi.

      If you've got a vacuum section on your boost gauge (if you've got one), what does it read?

      so if i set my fpr to 34psi (because -.6bar due to 20hg" at idle) that would act as a normal 3 bar stock fpr? 2.4bar=34psi

      Quote Originally Posted by macleanshaun View Post
      Imagine a really fat girl putting on a big belt around her stomach, but tightening it WAY too tight. Her stomach will push both up and down out of the belt.
      haha

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      04-06-2008 12:31 AM #5
      Just keep it simple...
      1. With the engine idling, disconnect the vacuum/boost reference line connected to the FPR
      2. Temporarily plug the reference line to prevent a vacuum leak
      3. Adjust the FPR until you achieve 3 bar fuel pressure
      4. Remove the plug from the reference line and reconnect the line to the FPR
      5. Enjoy
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      04-06-2008 01:04 AM #6
      what he said take off the vaccum line hold it closed with your thumb adjust fuel pressure to desired psi or 3 bar. then put the vaccum line back on

      good to go

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    7. Member mveitenheimer's Avatar
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      04-07-2008 01:26 AM #7
      Quote, originally posted by bdcoombs »
      what he said take off the vaccum line hold it closed with your thumb adjust fuel pressure to desired psi or 3 bar. then put the vaccum line back on

      good to go


      thanks that worked great !!!
      Quote Originally Posted by macleanshaun View Post
      Imagine a really fat girl putting on a big belt around her stomach, but tightening it WAY too tight. Her stomach will push both up and down out of the belt.
      haha

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      03-12-2012 11:58 PM #8
      I know this is old but none the less.

      What adverse affects could I see if my base fuel pressure is off by 2-3 psi give or take?
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      03-13-2012 12:01 PM #9
      Quote Originally Posted by derekb727 View Post
      I know this is old but none the less.

      What adverse affects could I see if my base fuel pressure is off by 2-3 psi give or take?
      nothing. fueling would be off a tiny tiny bit

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