An old idea but there has been some recent developments
   that might make it work. The idea is to measure the EGT
   and use that to adjust the mixture.

   The computer can increase the mixture and check the EGT.
   If the EGT goes up your EFI system is on the rich side
   of the EGT verses mixture curve. See the attached JPG.

   If the EGT goes down your system is on the lean side
   of the curve. It takes a few minutes to do this as the
   EGT probes are not very fast.

   It is easy to program this situation in BASIC as once
   the computer knows what side of the curve it is on
   it can tune for minimum fuel burn or max power.

   There needs to be a button on the instrument panel
   telling the computeryou want to lean for max MPG.
   Call it the leaning button. The default is maxpower.
   If you push the throttle all the way in it can go
   back to max power using a micro switch.

   Here is a circuit that will put out 5 millivolts per degree
   C. Feed it into the ARM A to D pin.

   Paul Lamar




Some car EFI systems have a similar feature using a wideband O2 sensor. It would be as easy or easier to implement and much more accurate. The output of the sensor I am familiar with is programmable so that it can be 0-1v or 0-5v or anything in between.

Josh Jacops

That should be simpler. What is the price now?
We could do both.  More information never hurts.
Which one do you use?

Paul Lamar