Suggestions on altitude compensation for mechanical FI system wanted...

[Gary Derian]

Are you doing hillclimbs or does your commute have large elevation changes
in it?  Since you are metering strictly with shuttle movement, you have to
rig up some means of adjusting that movement with a barometer.  If the fixed
end of the shuttle can be accessed (its been a long time since I looked at a
Lucas mechanical system) perhaps some king of screw adjustment can be added
there.  If that side is buried inside the fuel distributor, you have to work
with the mounting points for the springs in the vacuum unit.  That unit
could be attached to a moveable piece that was controlled by a stepper
motor.  This motor could then be controlled to provide mixture control for
temperature, barometer, O2 sensor, etc.

Modifying the vacuum signal would be tricky since it varies all the time.
Perhaps an adjustable bleed, which would only richen it up, could be added.
The base setting could be set for high altitude and the bleed increased as
altitude decreased.

Gary Derian <gderian at cybergate.net>

-----Original Message-----
From: Michael D. Porter <mdporter at rt66.com>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Thursday, March 11, 1999 1:15 AM
Subject: Suggestions on altitude compensation for mechanical FI system
wanted...


>
>Okay, I know it's nuts... but I bought, mostly for nostalgia's sake, an
>older Lucas PI mechanical fuel injection system, made for the TR6 2.5
>liter inline six. After lots of queries on the Triumphs list, and of
>people in England, it seems there was some very crude altitude
>compensation built into later units, but that it didn't work very well.
>
>The metering unit uses a baseline spring and cam calibration which is
>controlled by manifold vacuum. Higher the vacuum, the less fuel delivery
>at the injectors... It's mostly just controlling shuttle movement, I
>think.
>
>Anyone have any interesting ideas on including workable barometric
>compensation on such a system? Digitally, it's fairly easy, at least in
>closed loop mode. As I recall, the older L-Jetronic Toyotas had a sealed
>bellows with a strain gauge inside which altered the closed loop
>resistance.
>
>But, given the vacuum control system of the Lucas mechanical system,
>something like that would not be feasible, unless it operated a valve
>controlling a vacuum reservoir or some such which fed the metering unit.
>
>Cheers.