Dudes,

me and some guys wonder, what the ecu does with the information from the air-mass sensor..
Does the ecu change the quantity of fuel relatively to the quantity of air that streams in ? Or is the quantity of fuel unchangable and an intake or K&N Filter will only affect better breathing ?

 

The AFR (Air/Fuel Ratio) of your engine has a significant impact weather your car is performance, economy, or emmision oriented. Here we will take a closer look at this subject.

The oxygen sensor detects the oxygen content in the exhaust gas and signals the ECU. In operation, the ECU receives the signal from the sensor and varies the duration during which fuel is injected. The oxygen sensor has an internal heater. The heater stabilizes the sensor's output." - Straight from the Honda Manual.

The purpose of oxygen sensor is strictly for emmision reasons. The conventional three way catalytic converter opeates in a narrow a/f window for optimum performance. Which happens to be 14.7:1 air to fuel ratio (at this ratio the mixture is also called "stoich"). All the mass produced oxygen sensor (also called narrow band because it is only accurate around stoich) have a response curve similar to the curve below (from Honda service manual).



Most ECU operates in two mode - close loop and open loop mode. Close loop means the ECU monitors the oxygen sensor and tries to maintain stoichmetry in order to ensure good emmision performance. When you go wide open throttle (gas pedal floored) ECU goes into the open loop mode which it ignores the oxygen sensor output. In open loop the ECU uses the fuel map programmed by the manufacture. These valves are more performance oriented and most engines make good power around the AFR of 12.5-13.0:1 or so. Honda motors are more efficient than most demostic cars, I have heard people think Honda motors like 13.0-13.5:1. I'm not really sure about that, but all we need is for somebody to have a wide range oxygen sensor setup and a dyno then we can know for sure.

 

Your answer is far more complex than what this guy is looking for.

Closed loop mode aside which is only used when on constant partial throttle, eg, cruising.

In open loop mode the ECU reads the MAP sensor (Manifold Absolute Pressure) and reads the RPM's. The ECU has a table of values that it checks, when the pressure is x amount and the RPMs are Y amount, then open the fuel injectors for Z amount of time.

Any modification that allows better breathing on the intake side will have the effect of changing the MAP reading to show more air being taken into the engine which will tell the ECU to give more fuel.

 

Also want to add, The fuel pressure regulator plays a part in all this also,, but ya he just open a can of worms.