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 --


I am familiar with the Innovate LC-1
(http://www.innovatemotorsports.com/products/lc1.php)  It's about $200
for the kit.  It mentions that it self-calibrates for temperature,
altitude, and sensor condition.  You can only calibrate it in free air
(or after exhaust fumes have been purged from the exhaust system), so
be aware of that.  I suspect you may have to build in some logic that
compensates for the reducing exhaust pressure as altitude increases.
Maybe not so simple an installation anymore.

Also, leaded race fuel has been known to coat the sensors rendering
them useless until they are cleaned.  I personally never had an issue
using leaded fuel on the weekends and unleaded on a regular basis.
AVGAS is low-lead, so it does not cause as big an issue, but still
limits sensor life.  Unless you are ok with replacing the sensor every
200 hours, i would suggest using mogas as much as practical.

Someone good with electronics like yourself could probably build your
own circuit for a few dollars and buy the sensor for $80 or so if $200
is hard to swallow.  Including a pressure transducer in the circuit
for on-the-fly calibration could then be accomplished.

There is a lot of good information about the common Bosch LSU4 sensors
here including lead and altitude effects:

http://wbo2.com/lsu/lsu4.htm

And here is the technical data sheet for one of them:

http://wbo2.com/lsu/Y258K01005e03mar21eng.pdf

That site also sells build-it-yourself kits that you may be interested in.

Josh Jacobs

Back to the EGT's. :)

Paul Lamar

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