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Old 02-24-2006, 08:59 AM   #1
IndyRacer
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Default Where is atmospheric pressure sensor located?

I have been doing some work on my intake system, and was wondering where exactly the atmospheric pressure sensor is located. Is it internal to the intake system, or does it measure underhood pressure, external of the intake system?

Since our boost systems are based on relative pressure, it would seem that any increase in atmospheric pressure would directly correspond to more absolute boost, and thus more power. I obviously can't change the actual atmospheric pressure, but if the sensor is in the intake system, there may be ways to artificially raise the value, or at least make sure it is not lower than actual atmospheric.
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Old 02-24-2006, 09:44 AM   #2
Jon [in CT]
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There's a barometric pressure sensor on the ECU's circuit board and a manifold absolute pressure sensor just behind the throttle.
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Old 02-24-2006, 10:11 AM   #3
IndyRacer
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Thanks Jon. Not the answer I was hoping for, but the answer none the less.

Now, how does the ECU adjust boost (manifold relative pressure) to account for differences in atmospheric pressure? Does it use the sensor in the ECU to account for elevation changes, weather, etc.
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Old 02-24-2006, 10:14 AM   #4
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the atmospheric pressure is sensed by the map sensor after ignition power is applied but before the engine turns over.
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Old 02-24-2006, 10:14 AM   #5
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Quote:
Originally Posted by Jon [in CT]
There's a barometric pressure sensor on the ECU's circuit board and a manifold absolute pressure sensor just behind the throttle.
jon, are you sure there's actually a sensor on the oem ecu board?
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Old 02-24-2006, 11:16 AM   #6
hondaeater69
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for reference the stock barometric compensation table for WGDC looks like this:


baro- 8.51 9.75 10.98 12.22 13.36 14.7
WG% 18.75 18.75 18.75 18.75 18.75 0.00

expressed as a % added to WGDC.



Boost limits are also cut under lower atmospheric pressure.
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Old 02-24-2006, 12:20 PM   #7
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Quote:
Originally Posted by ride5000
jon, are you sure there's actually a sensor on the oem ecu board?
Yes. For instance, the only step in the diagnosis of a P1110 trouble code (Atmospheric pressure sensor low input) is to replace the ECU.
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Old 02-24-2006, 12:38 PM   #8
ride5000
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very interesting!

well in that case, strike my earlier comments on it determining atmospheric pressure via the underhood MAP sensor.
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