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Thread: Map sensor reading low

  1. #1
    Advanced Tuner KFXGUY's Avatar
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    Map sensor reading low

    2004 GTO LS1 auto
    Turbocharged
    2 bar factory GM cobalt ss sensor
    2 bar custom os
    Map sensor linear is set at 210kpa, was as the default 200kpa and same thing. Map sensor offset is default of 10.33kpa

    So my map sensor reads off after 110kpa. In my chart, when it starts to wonder off, it reads 110kpa, my afr histogram reads 120kpa. As soon as it hits 115kpa, the histo now says 130kpa. 120.1 it says 140, 125.2 now reads 150.... And so on. The afr kpa is correct because that what my boost controller and boost gauge say. Help me understand what I need to change to make this fall in line, please.
    2004 5.7 gto
    7875 turbo
    Heads/cam

  2. #2
    Tuning Addict 5FDP's Avatar
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    By chance are you logging 2 different MAP channels?

    Only the 2 bar channel can be logged, if more than one is in there it can skew the rest of the readings.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Advanced Tuner KFXGUY's Avatar
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    Well that could be possible. BUT when I change the fueling in my tune, if I want to change fueling in the 190kpa range, I actually have to change it in the 150kpa range. If I change it in the 190 range, it makes no difference. So my tune falls in line with the lower map even tho I?m really at 12lbs boost. So my map sensor isn?t calibrated correctly is my suspicion. I just need to know what I need to do to calibrate it correctly.

  4. #4
    Tuning Addict 5FDP's Avatar
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    You have the linear and offset settings correct, not much else you can do with calibration on the MAP.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  5. #5
    Advanced Tuner KFXGUY's Avatar
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    Just to make sure, I deleted my current channels and then added a two bar channel back. But I don?t think that will affect my fueling kpa in my tune. I?ll drive it to work tomorrow and run a log. But if anyone else knows what my problem may be, I?m all ears.

  6. #6
    Senior Tuner cobaltssoverbooster's Avatar
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    Have you checked your wideband delay?

  7. #7
    Advanced Tuner KFXGUY's Avatar
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    Quote Originally Posted by cobaltssoverbooster View Post
    Have you checked your wideband delay?
    Not sure how to do that but I can tell you this, as soon as I see the lean out, I feel it nose over. So if there?s a delay, it ain?t much. That still wouldn?t have anything to do with the fact that in the tune, if I change my fueling in the 180-190kpa range, it makes zero difference in my afr. But if I change it in the 150kpa range, it makes whatever change I make, for 180-190kpa. According to my boost gauge and my boost controller gauge. So I know without a doubt, the calibration of the map is off. I just don?t know which way I need to go with it to bring it in line. I could experiment, but running the crap out my car repeatedly is not something I really want to do.

  8. #8
    Senior Tuner cobaltssoverbooster's Avatar
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    hold it in steady state in boost. if the data adjust where its recording in steady state then you have an o2 delay.
    if steady state isnt correct still then unbolt your sensor and perform this data collection steps:
    key on, engine off, scanner connected and reading channels
    your going to monitor voltage so get a pen or make an excel sheet.
    1) record free air pressure from local source such as local airport or local weather station. Later you will check your koeoff map reading to verify you are close to your local readings.
    2) use a vacuum tester to pull 15" and 20" of vacuum. record voltage at each point.
    3) use shop air to blow pressure into the sensor. i watch voltage and try to take a reading when the source pressure makes the output voltage read 3.5 and 4.2-4.5 volts. using shop air you need a source to tell you accurate pressure...i have a tube i pressurize that i keep a longacre digital pressure gauge installed in. this gives me a psi readout.
    if you cant test accurately with a shop air source then perform step 2 but collect data at 3" 6" 9" 12" 15" 18" 20"....

    if you convert the vacuum and psi readings to kpa then you can plot the kpa per voltage in an excel scatter graph. tell the graph to make a line of best fit 'linear' and modify the best fit line properties to show equation on graph. this equation becomes your linear calibration data for your sensor. (y=mx+b where b is your sensor offset and the difference from the y values at 0 and 5 become your linear 5 volt range. (y value at x=5) - b value = 5 volt range.

    insert data into editor file and check against value from step 1. you should be fairly close.
    Last edited by cobaltssoverbooster; 04-23-2019 at 01:06 AM.
    2000 Ford Mustang - Top Sportsman

  9. #9
    Advanced Tuner KFXGUY's Avatar
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    I?m not sure what I did, but it appears to be working correctly now.