TPS and RPM only?

[Tom Cloud]

>It seems to me that if you just use TPS and RPM, you wouldn't be able to
>compensate for load at various speeds.  Unless you feed back O2 readings,
>wouldn't the engine tend to run rich at low loads?

The ProJection seems to work fine for me, and it only uses TPS
and RPM.  In some ways it's more quirky than a carb, but I've
run it for over a year, and through two winters.  The winter is
when it's quirkiest ... namely the choke enrichment doesn't always
seem to work right, but once it's warmed up and/or at speed, it has
always worked okay.

The way I imagine the TPS/RPM only thing is, I visualize a straight
line on a graph.  Independent var (x-axis) is RPM, dependent var
is fuel.  Higher speed = more fuel.  Do the same for TPS.  More
throttle = more fuel.  Now, add those two.  If you're under load,
you'll have lower RPM, but higher TPS, so you still get more
fuel.  The ProJection has a delta-TPS (throttle pump) function
that injects more fuel when the throttle is rapidly pushed to
avoid stalling.

I have monitored this setup with an EGO and DPM since it was
first installed.  It has always worked fine.  It doesn't work
at stoich.  Rather, it's lean for cruise or decell and rich
for accel, which is what I want.  An EGO feedback can be added,
and I may do that some day so I'll have some automatic adjustment
when I go to the mountains and altitude changes.

Tom Cloud <cloud at peaches.ph.utexas.edu>