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MAP sensor, whats it do, what are symptoms

This is a discussion on MAP sensor, whats it do, what are symptoms within the Technical / Maintenance forums, part of the General Discussion category; What exactly does this little pos do and whats it control? What symptoms do I look for if its bad?...

  1. #1
    loves Mickie James oldred95's Avatar
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    MAP sensor, whats it do, what are symptoms


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    What exactly does this little pos do and whats it control? What symptoms do I look for if its bad?
    1995 Silverado - ported vortec heads, 4L80E, efans, LT4 Hot Cam, Rear disc brake conversion w/drilled and slotted rotors
    1999 NBS Silverdo - transgo HD2 shift kit, 3 inch dynomax ultra flow, Ford keys and 305/70-16 Mickey ATZs

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    Registered User 98crewcab's Avatar
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    Re: MAP sensor, whats it do, what are symptoms

    here is a link for information on the MAP sensor

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    loves Mickie James oldred95's Avatar
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    Re: MAP sensor, whats it do, what are symptoms

    Quote Originally Posted by 98crewcab
    here is a link for information on the MAP sensor

    http://members.iatn.net/tech/gm/gmfid/3-7.html
    Says I have to be a member and login to view it.
    1995 Silverado - ported vortec heads, 4L80E, efans, LT4 Hot Cam, Rear disc brake conversion w/drilled and slotted rotors
    1999 NBS Silverdo - transgo HD2 shift kit, 3 inch dynomax ultra flow, Ford keys and 305/70-16 Mickey ATZs

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    Registered User 98crewcab's Avatar
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    Re: MAP sensor, whats it do, what are symptoms

    Manifold Absolute Pressure (MAP) Sensor

    The Manifold Absolute Pressure (MAP) sensor is a three-wire sensor. It is located in the engine compartment and connected to intake manifold pressure (vacuum)

    The PCM uses MAP information for:

    Fuel delivery
    Spark calculations
    Barometric pressure readings
    EGR diagnostics
    The MAP sensor measures changes in intake manifold air pressure. The PCM uses information from the MAP sensor, which indicates engine load, in order to calculate fuel and spark timing requirements.

    Manifold absolute pressure is the exact opposite of manifold vacuum. That is, MAP is low when vacuum is high (such as at closed throttle), and MAP is high when vacuum is low (such as at wide-open throttle). When the engine is not running, the manifold is at atmospheric pressure and the MAP sensor is registering barometric (BARO) pressure.

    The BARO reading is used at engine start-up for fuel delivery calculations, as well as during engine run for fuel and spark calculations.

    The PCM updates its Baro reading when the ignition is turned on and when the accelerator is at wide open throttle.



    Strain Gauge MAP Sensor
    The MAP sensor currently being used on GM systems is the strain gauge type. This sensor contains a silicon chip, approximately 3mm square. It is placed in a sealed housing which is connected to the manifold. A fixed pressure is sealed above the silicon chip and manifold (atmospheric) pressure is below it. When the engine is running and manifold vacuum is created, the pressure below the chip drops, creating a change in resistance.

    In operation, constantly varying vacuum from the intake manifold is applied to the sensor housing. Any change in applied vacuum causes a corresponding change in the sensor’s resistance. Electrically, when manifold pressure is low, such as at idle, the sensor voltage is low, perhaps 1 volt. When manifold pressure is high, such as at wide-open throttle, sensor voltage is high, perhaps 4.5 to 5 volts

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    Re: MAP sensor, whats it do, what are symptoms

    MAP = Manifold Absolute Pressure it basically tells the computer what the vacuum of the engine is and based on RPM and other variables your computer can accurately gauge the engine's load and adjust the fuel accordingly. A bad MAP will throw a code and you should run REALLY rich all the time.

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    loves Mickie James oldred95's Avatar
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    Re: MAP sensor, whats it do, what are symptoms

    Well I'm not gettin a code and I don't think its running rich. I did a search on google and it said that by unplugging the MAP sensor, the ECU will automatically run off a preset MAP setting. I think I may try this and see what happens. The only time it really acts up is when the engine is under a load (idling in gear, acceleration, cruising into head wind) and from what I've read the MAP sensor is operated off engine load (vacuum). I think I will try unplugging it and see what it does.
    1995 Silverado - ported vortec heads, 4L80E, efans, LT4 Hot Cam, Rear disc brake conversion w/drilled and slotted rotors
    1999 NBS Silverdo - transgo HD2 shift kit, 3 inch dynomax ultra flow, Ford keys and 305/70-16 Mickey ATZs

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    Big Block Chevy's Rule!
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    Re: MAP sensor, whats it do, what are symptoms

    Why do you think the MAP sensor on your truck is bad?
    90 460SS CC266HR cam/Edel 049 alum heads/alumRRs/Ross forged pistons/9.6CR/Edel intake/JET AFPR/Edel WP/Edel 6660 headers/March pulleys/MSD6a/coil/wires/GMPP dist & starter/SuperTrapp dual exhaust/Built TH400, & 97 Camaro SS 390rwhp

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    loves Mickie James oldred95's Avatar
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    Re: MAP sensor, whats it do, what are symptoms

    Because I've been having this missing/stalling/terrible idle/shudder problem and I've tried a good TPS and IAC off another truck and that didn't help. I've checked the EGR and even plugged it off with a screw but that didn't help. The map sensor controls the timing and fuel and what not and I've got a problem with timing or fuel to cause my problem so the MAP sensor is my next guess. BTW, I have completely eliminated the ignition system and the fuel system. The problem has to be one little sensor somewhere.
    1995 Silverado - ported vortec heads, 4L80E, efans, LT4 Hot Cam, Rear disc brake conversion w/drilled and slotted rotors
    1999 NBS Silverdo - transgo HD2 shift kit, 3 inch dynomax ultra flow, Ford keys and 305/70-16 Mickey ATZs

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    Registered User 98crewcab's Avatar
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    Re: MAP sensor, whats it do, what are symptoms

    I guess we are talking about your 95 truck?
    OBD1?
    Do you know if the plug wires are wired correctly?
    Also have you pulled the all plugs to see how they look.
    I would start there first.
    You can also put your DVM on the oxygen sensor to see if it changing voltage.
    Usually from .03-.08 Millivolts… let us know what the plugs look like
    ?

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    loves Mickie James oldred95's Avatar
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    Re: MAP sensor, whats it do, what are symptoms

    Plugs are almost new, maybe 1000 miles on them, wires are maybe 3000 miles on them, everything else is new to. Go here to get the latest details on how my truck is running. http://www.fullsizechevy.com/forums/...55#post1444855
    1995 Silverado - ported vortec heads, 4L80E, efans, LT4 Hot Cam, Rear disc brake conversion w/drilled and slotted rotors
    1999 NBS Silverdo - transgo HD2 shift kit, 3 inch dynomax ultra flow, Ford keys and 305/70-16 Mickey ATZs

  11. #11
    Big Block Chevy's Rule!
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    Re: MAP sensor, whats it do, what are symptoms

    Some things to check:
    Ground straps and connections
    Engine temp sensor
    Air leaks particluarly the two gaskets under the TBI
    Distributor; if you have high mileage you might want to replace it anyway.

    You need to be able to check for codes or access a scanner for more info.
    90 460SS CC266HR cam/Edel 049 alum heads/alumRRs/Ross forged pistons/9.6CR/Edel intake/JET AFPR/Edel WP/Edel 6660 headers/March pulleys/MSD6a/coil/wires/GMPP dist & starter/SuperTrapp dual exhaust/Built TH400, & 97 Camaro SS 390rwhp

  12. #12
    loves Mickie James oldred95's Avatar
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    Re: MAP sensor, whats it do, what are symptoms

    Checked all of those and I check for codes with a paper clip and there were none until I unplugged the MAP.
    1995 Silverado - ported vortec heads, 4L80E, efans, LT4 Hot Cam, Rear disc brake conversion w/drilled and slotted rotors
    1999 NBS Silverdo - transgo HD2 shift kit, 3 inch dynomax ultra flow, Ford keys and 305/70-16 Mickey ATZs

 

 

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