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  1. #1
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    questions about AFR and Vac.

    i have a few general questions, i was experiencing a lean condition while cruising. idle AFR's were rock solid as well as WOT, cruising was rock solid under 2500 RPM's but above that my AFR's were jumping in and out of the 16.5 to 17.5 range while holding a steady pedal. as soon as i would push the throttle harder it would richen back up. thought it was a fuel pump but checked my fp and it was 65-68ish off throttle and 72ish on throttle so that wasnt it.......long story short it finally coded a crank position sensor which ended up being the culprit, i guess it was reading bad and the vanos was going nutso with the timing and fuel.

    this got me to looking at my guages regularly and i noticed something i havent before on my vac. guage. im not sure if its normal or not so thought i would ask a few of you with guages.

    at idle my vac reads 20 steady, except when i turn on the a/c it drops to 18 steady. is this normal for the a/c compressor to effect idle vac readings?

    also is 20 vac at idle right. i seem to remember at one time i was around 22 idle. when im driving if i quickly let off the accelerator and let the throttle plates slap shut it pulls 22.
    Click here to enlarge Originally Posted by TwinturboM3
    I bang the chickens on my farm 60-130 times a day.
    Click here to enlarge

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    Wish I could help, bumping as I think ccysykes may be able to shed some light on this.

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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Wish I could help, bumping as I think ccysykes may be able to shed some light on this.
    Sounds right to me.. mine does the same thing. AFR's are in the 14-15's when cruising.

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    Click here to enlarge Originally Posted by ccsykes Click here to enlarge
    Sounds right to me.. mine does the same thing. AFR's are in the 14-15's when cruising.
    Sounds like he has nothing worry about then and it is normal.

  5. #5
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    Click here to enlarge Originally Posted by Funkboy316 Click here to enlarge
    i have a few general questions, i was experiencing a lean condition while cruising. idle AFR's were rock solid as well as WOT, cruising was rock solid under 2500 RPM's but above that my AFR's were jumping in and out of the 16.5 to 17.5 range while holding a steady pedal. as soon as i would push the throttle harder it would richen back up. thought it was a fuel pump but checked my fp and it was 65-68ish off throttle and 72ish on throttle so that wasnt it.......long story short it finally coded a crank position sensor which ended up being the culprit, i guess it was reading bad and the vanos was going nutso with the timing and fuel.

    this got me to looking at my guages regularly and i noticed something i havent before on my vac. guage. im not sure if its normal or not so thought i would ask a few of you with guages.

    at idle my vac reads 20 steady, except when i turn on the a/c it drops to 18 steady. is this normal for the a/c compressor to effect idle vac readings?

    also is 20 vac at idle right. i seem to remember at one time i was around 22 idle. when im driving if i quickly let off the accelerator and let the throttle plates slap shut it pulls 22.
    Yes this is normal, your motor has to add some throttle/fuel to keep up with the extra load of the AC compressor and evaporator fan motor.

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    Normal Click here to enlarge 20 vac is where you should be at idle

  7. #7
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    drove the $#@! outta the car last night, for the first time after fixing the Crank pos. sensor.............amazing how one little sensor can make the car run like complete ass.........car feels great now and all my AFR reading are back to spot on.
    Click here to enlarge Originally Posted by TwinturboM3
    I bang the chickens on my farm 60-130 times a day.
    Click here to enlarge

  8. #8
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    Click here to enlarge Originally Posted by SlicktopTTZ Click here to enlarge
    Yes this is normal, your motor has to add some throttle/fuel to keep up with the extra load of the AC compressor and evaporator fan motor.
    gonna say the same thing, what vac it is supposed to be, i cant asnwer. What its showing is also up the the guage and what the guage is set to read at. For instance, my p3 can go to -60, but i have it set at a limit of -24 so thats all i would see,in park/neutral. in gear @ idle, ill see anywhere from -17 to -14 depending on conditions (AC included)

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