Aftermarket EFI, speed density etc.

[Matthew Lee Franklin]

Peter wildly guessed:
>First the threottle position is the correct way, then the MAP sensor.
>It seems that Robert is going to be right no matter what the answer is.

Robert is quite correct here, as usual.  MAP is far more useful than 
throttle position, if it can be measured.  For a given throttle setting you 
could have a wide range of manifold air densities.  For a given MAP the 
intake density is pretty well nailed down (and even better with an ideal 
gas correction from the MAT).

In fact, you could do a simple control without a map.  Just make fuel 
injection pulse width a linear function of MAP.  It's like a one-hole map.  
If you really wanted to, you could estimate rho = P/(R*T) with the help of 
a MAT sensor, too.  (This assumed that volumetric efficiency doesn't change 
with speed, but a simple 3rd or 4th order V.E. vs. RPM curve would probably 
correct for that, too.)   

Things like this are probably better left to mechanical engineers with a 
strong EE emphasis (or EE's with a strong ME emphasis), and not marketing 
guys.

Later,
Matt