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Old 12-05-2009, 08:22 PM   #1
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Default MAP sensor and weather changes

Heey there all,

So I was in Kure Beach, NC for the past couple of weeks and noticed something strange... When driving on a nice and sunny day, the car runs great and idles fine. Noticed that we had a storm coming in while driving and sonnofabitch if the car was being a ***** in the rain...

Seems that maybe with the barometric pressure change my MAP maybe was not calibrated or something? I don't quite know what to look for here when there is a weather system coming; but this is 3 times now that the car got really angry with a storm approaching.

Does anyone else here have this issue and what are you doing to quash the impact?

Thanks all and cheers,
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Old 12-05-2009, 10:47 PM   #2
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What are the symptoms? It would be interesting to see datalogs from both scenarios.
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Old 12-06-2009, 12:18 AM   #3
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I don't think the barometer changing with the weather has anything to do with it, but for ***** & giggles I looked up some numbers. The one place in the continental US with the biggest spread between its all-time record high and low barometer readings has a difference of 3.21 inHg, or about 11 kPa. But unless you have some really uncommon weather (probably too uncommon for you to experience three times with your car, but I'm no meteorologist) the barometer more typically stays within a range +/- 20 millibars (2 kPa). Even if your MAP sensor was that much off, it wouldn't make the car drive extremely weird.

But this is all besides the point, which is that your MAP sensor reads absolute pressure in the manifold. If the barometer drops, then I'd think your MAP at idle would also drop a little and the sensor should pick that up. The weather is an interesting observation but I think there may be something else going on. Maybe you drive less aggressively in the rain and your part throttle cells aren't tuned as well. Where's your IAT sensor mounted? Maybe rain water is hitting it and causing weird readings. I agree that you should definitely datalog this phenomenon when it happens.
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