[Diy_efi] Newbie with a simplified Motronic project

[Tlsalt at aol.com]

Eric D Byrd wrote,

One thing I don't get about MAF vs. MAP.  Everyone's making out like MAF
is self-correcting, and never any longer any need for fuel trim tables. 
How?  Both are sensors, that respond to a physical phenomenon by
generating a voltage, and all such devices experience variations in
response due to age.  MAF is no different.  The fuel map in the ECu is
fixed, and eventually the MAF will signal a slightly different value for
the same air flow, and the ECU will send a different fuel pulse.  Why
don't MAFs require fuel trim tables?  From the post below, it appears
they do, and that they get them from feedback from the O2.  And that is
no different from a MAP.

Hello Eric,

The point is not about the sensor wearing and generating a false signal, it 
is about the engine wearing and the ECU's ability to compensate.  MAF is 
measuring something directly related to fuel quantity and if a worn engine is 
pulling in less air mass at a certain load, the ECU will provide the correct 
fuel, within a range. All the MAP sensor knows is to look up a pulse width 
for a certain manifold pressure.  The pulsewidth is fixed for each pressure 
point and the ECU assumes it is correct.  This is only an issue for 
manufacturing, mass produced engines that need to meet emission standards 
without attention for 50,000 miles.  The MAP is a much better idea for a 
programmable, performance system.  It is a more reliable, less expensive 
sensor and if the fuel map is correct, it will outperform a MAF system 
because it has less restriction. 

Remember most system only operate closed loop at less than 30% throttle and 
the O2 loop is not designed to correct bad fuel mapping.  There are no "self 
correcting" closed loop systems for turbos under boost.   Fueling under boost 
is more about cooling that maintaining a narrow chemical balance for the 
efficiency of a converter.


Paul

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