So last night, I installed the $45 MAF from the VW parts bin and here is my findings....
07-30-2002, 05:20 AM
#11
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Anybody know if you can get this part through Hitachi instead of junk Bosch?
I heard they were making Hitachi MAFS for S4s now which supposively are better quality...any thoughts on another source other than bosch?
07-30-2002, 09:13 AM
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I'm guessing that the thermistor is used as an ambient temperature sensor...
since this version of the maf might not have an external (input, correction ->
output for temperature correction. This sensor might drift more with external temperature fluctuations and the ECU might not be able to correct for it since there is no temperature output to the ECU.
output for temperature correction. This sensor might drift more with external temperature fluctuations and the ECU might not be able to correct for it since there is no temperature output to the ECU.
07-30-2002, 11:15 AM
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Made a correction to my above statement. The maf sensor works on the principle of hot film...
anemometry. I'm not an expert in this but this is how I think it works...
A heated element is placed in the flow stream (sensor head) where it is maintained at a constant temperature differential relative to the ambient air temperature. The amount electric power required to maintain the heated element at the target temperature is a direct function of the mass flow rate passing over the sensor head given the cross sectional area of the housing.
The maf sensor circuitry is a full bridge and the voltage across it must be balanced. Temperature sensitive resistors (thermistors) are used as both the ambient temperature sensor and heated sensing elements. Half the bridge is hidden from the flow whereas the other half or ¼ is exposed to the flow therefore it cools off so it takes more electric power to balance the voltage across the bridge. This process is done by the circuitry within the sensor. But the sensor and intake system are calibrated for a wide temperature range and I think this data lives in the ECU and final corrections are made to the data after the processor samples the maf sensor. I would be surprised if this process occurs inside the sensor itself. The sensor must have an embedded processor and storage for it to look up temperature correction.
A heated element is placed in the flow stream (sensor head) where it is maintained at a constant temperature differential relative to the ambient air temperature. The amount electric power required to maintain the heated element at the target temperature is a direct function of the mass flow rate passing over the sensor head given the cross sectional area of the housing.
The maf sensor circuitry is a full bridge and the voltage across it must be balanced. Temperature sensitive resistors (thermistors) are used as both the ambient temperature sensor and heated sensing elements. Half the bridge is hidden from the flow whereas the other half or ¼ is exposed to the flow therefore it cools off so it takes more electric power to balance the voltage across the bridge. This process is done by the circuitry within the sensor. But the sensor and intake system are calibrated for a wide temperature range and I think this data lives in the ECU and final corrections are made to the data after the processor samples the maf sensor. I would be surprised if this process occurs inside the sensor itself. The sensor must have an embedded processor and storage for it to look up temperature correction.