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Good question.

The AFM relies on the air coming into the engine to cool a heated wire. The air in the IC piping is, in general, going to be HOTTER than the air coming into the Air Box / Pod. If the air is hotter, it won't cool the AFM sensor as much. Therefore the ECU thinks there is LESS air than there really is. So, it reduces the fuel.

ping, ping, ping. BANG!

Is this the right reasoning as to why Mr Nissan didn't mount the AFM in the IC piping?

Actually the hot wire flowmeters have two heated wires. One is in still air, and the other in the moving airstream. Airflow is the difference in temperature between the two wires. That way ambient temperature changes cancel out.

But I think you are right. Placing the flowmeter after the turbo will give sudden extreme spikes in temperature that would probably cause large short term errors in reading the airflow.

A flap type flowmeter might be better, but high boost pressure may burst it !

  • 2 weeks later...

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