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correcting your AFR

EFI Tuning Fundamentals

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last night i started my question by stating i was confused but then amended that to claiming i had figured it out as i writing out my question. now i think i might have been a bit premature in reconciling my query. you match your actual lambda to target lambda by increasing injector pulse width to match the fuel required to satisfy a particular cell VE. BUT... you are not actually changing the VE are you??? my understanding is that VE is a function of swept volume and MAP or MAF independent of whether fuel is being delivered or not. am i wrong. is VE a function of actual firing of a cylinder. thanx blake

Correct but you dont actually know the VE of the engine. So you are calibrating the VE table to match your actual engines VE using measured lambda.

The ECU knows how much fuel it is injecting and it knows what air-fuel ratio it is aiming for so the only unknown is the mass of air it is inhaling. So if you adjust the VE table number until the measured lambda matches the target lambda then that means the ECU is calculating the correct air mass so the VE number must then be correct.

Obviously it is not as simple as that as there are many assumptions made and there are lots of other factors that effect air and fuel mass that arent even considered but that is the basic theory.

Using VE is an abomination in this application - it is the actual vs fully filled cylinder air mass.

What should be used is MASS Eficiency - the relative mass of air (oxygen) entering the cylinder Vs 100% fill of ambient air mass.

As Adam said, it is using two values to allocate a third value.