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Old 03-18-2008, 08:25 AM   #1
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Default MAP sensor readings

Not sure if this is the right area, so move if needed.

I'm working with the author of Proscan software. I'm told from people here that my pressure readings are wrong. Here'* what I was told. So if anyone has the answers to this, please get them to me and I'll pass them on. Thanks.

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I pulled my SAE papers to double-check the MAP sensor calculations, and ProScan is reporting the MAP sensor correctly.

The MAP sensor returns a single byte whose value represents the pressure from 0kPa to 255kPa. At idle, your MAP is returning 0x24 which corresponds to 35kPa (5.08psi).

The MAP sensor returns the absolute pressure value, so I guess the pressure could be -5psi at idle, and then other differences could be associated with the positioning of your boost pressure sensor and the MAP sensor itself. I'm not familiar with supercharger setups, so maybe someone else can offer a better answer. I'd try posting on or searching some popular forced induction forums, and if you find additional information please post it back here.
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Old 03-19-2008, 12:17 PM   #2
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This is the closest I've been able to come on any figures...

The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold vacuum. The MAP sensor signal voltage to the PCM varies from below 2.0 volts at idle to above 4.0 volts with the key on and the engine not running, or the engine running at Wide Open Throttle (WOT) .

A section on testing said that at idle the pressure/voltage can range from 20-48kPa/0.75-2 volts, depending on altitude.
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Old 03-19-2008, 12:50 PM   #3
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Originally Posted by Archon
This is the closest I've been able to come on any figures...

The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold vacuum. The MAP sensor signal voltage to the PCM varies from below 2.0 volts at idle to above 4.0 volts with the key on and the engine not running, or the engine running at Wide Open Throttle (WOT) .

A section on testing said that at idle the pressure/voltage can range from 20-48kPa/0.75-2 volts, depending on altitude.
The real question here is, does the MAP readings corrispond to boost? 10 pounds of boost is giving me a reading of 25 pounds from the MAP. Should a MAP sensor be reading a vac. at idle, (about -9 according to my boost gauge), or the +5 I'm getting on my scanning software?
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Old 03-19-2008, 01:11 PM   #4
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As I understand it, the MAP sensor does correspond to boost. I believe that your year had a separate MAP sensor specifically to read that. The 2000+* only have one, so my knowledge there is limited. This is another description of the operation of the MAP from a '98 Regal GS.

Description and Operation

The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure. The PCM supplies a 5 volt reference and ground for the MAP sensor. The MAP sensor circuit provides a signal to the PCM relative to pressure changes in the manifold. With the key ON, engine not running the MAP sensor signal voltage to the PCM varies between 1.5 to 2.5 volts. With the engine running, the MAP sensor voltage to the PCM varies from below 2 volts at idle (low manifold absolute pressure - high vacuum) to above 4 volts at wide-open throttle (high manifold absolute pressure - low vacuum).
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