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About MAP Downside

EFI Tuning Fundamentals

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“ 07:33 One downside with using a MAP sensor is that the speed density calculation assumes that the relationship between airflow and pressure remains constant.

07:42 What this means is that if an engine is correctly tuned using a MAP sensor and then some mechanical aspect of the engine is changed resulting in increased airflow there's no way for the ECU to know this and the result could be an inaccurate air fuel ratio.”

Does changing a boost level means a “mechanical aspect of the engine that has been changed "?

Thank you:)

What they mean is that modifying the engine changes the Volumetric Efficiency. And then your MAP table isn't correct anymore.

If you're just raising the boost and not changing anything else, then you're not really changing the VE. Your table will still be correct for all the parts that are mapped. However if you raise the boost above what's been previously tuned, then you'll need to fix that area of the table.

Some ECUs are actually using fuel closed loop mode to maintain the commanded lambda value by using wbo2 sensor - that is optional feature...

Think more along the lines of changed cam(s), cam/port timing, intake filter/intercooler restriction, exhaust backpressure. An IMP:EMP based main load/VE table will assist with compensating for system elements external to the engine but not cam/port changes, MAF is required to capture that accurately.