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MAP sensor calibration

Discussion in 'FAST Support Forum' started by hwholder, Apr 3, 2019.

  1. hwholder

    hwholder New Member

    Joined:
    Aug 17, 2013
    Location:
    Blanco, Texas
    I have XFI.
    My FAST MAP sensor is a 3 bar FAST sensor and the calibration values are in accordance with the XFI manual.
    Without the engine running the MAP sensor reads 94 kPa and Raw MAP(V) is 1.51.
    The barometric pressure at the time of this reading was 30.22 In Hg which is 102.3 kPa.
    I have a new 3 bar FAST sensor (spare) that I plugged in and got the same readings.
    I have 5 vdc and a good ground going to the MAP sensor.
    The calibration is linear - 0.00 @ 0 kPa to 5.00v @ 315 kPa.
    Questions:
    What causing the difference between what the MAP sensor is saying vs the actual?
    Is there a different calibration than the one in the manual which is what I have set up?
    Could there something wrong with the ECU that would be causing this?
     
  2. Fastmanefi

    Fastmanefi Well-Known Member

    Joined:
    Jun 4, 2011
    Location:
    Sonora, CA
    It's not unusual for map readings to be a little off. The error increases with the map sensor range. I would just correct the calibration manually and go from there.
     
  3. hwholder

    hwholder New Member

    Joined:
    Aug 17, 2013
    Location:
    Blanco, Texas
    Thanks for the reply.
    Is the difference in readings between real pressure and what the ECU is seeing from the MAP signal messing with the VE table?
    I have a pretty solid VE table right now - a substantial effort to get it tuned.
    I guess I can calibrate from atmosphere pressure to 30 psi and then check the shape the graph with a few points in between.
    Should I expect the calibration graph to be linear?
    When I recalibrate the MAP sensor in the XFI will that require that I rework my VE table and/or any other MAP related settings?
     
  4. Fastmanefi

    Fastmanefi Well-Known Member

    Joined:
    Jun 4, 2011
    Location:
    Sonora, CA
    Is the difference in readings between real pressure and what the ECU is seeing from the MAP signal messing with the VE table?
    Not really. VEs are just reference information. As long as the AF and timing are correct you'll have a good tune.

    I guess I can calibrate from atmosphere pressure to 30 psi and then check the shape the graph with a few points in between.
    Should I expect the calibration graph to be linear?
    "Sort of linear ...lol..." Actual results often have a slight bend to them. Temps sensors do this also.

    When I recalibrate the MAP sensor in the XFI will that require that I rework my VE table and/or any other MAP related settings?
    Maybe, since the numbers in the table don't change their position even though the axis values have. But the change is usually small enough that Learn will take care of it.
     
  5. hwholder

    hwholder New Member

    Joined:
    Aug 17, 2013
    Location:
    Blanco, Texas
    Thanks for the help
     

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