Old business....

[Michael D. Porter]

Ages ago, I submitted a question to the folks here about barometric
compensation on an old Lucas mechanical PI (petrol injection) system,
and I received a couple of helpful answers based on what I proposed to
do to solve the problem (minor adjustment of the unit's datum cam to
compensate for altitude differences).

That was before I had the unit in hand, disassembled, and had
considered, carefully, how the unit worked mechanically. It's a horribly
and unnecessarily complicated arrangement of adjustments to do,
essentially, one thing--move the metering unit pintle to adjust mixture.
The only real variable input to the entire system is vacuum. (!)

What I am contemplating is to do some sort of series loop input to add a
MAP to calculate vacuum, air temp sensor, and perhaps include an engine
speed signal on another line. If it turns out that barometric
compensation isn't well-managed by the MAP, to also put a barometric
compensator in the loop, then have a Motorola 68HC11 controller make the
outputs to a servo motor actuating the pintle actuator barrel in the
metering unit. 

The question here is about compatible components. I'd like to be able to
find sensors compatible with each other, i.e., all highs and lows
compatible in the right direction--all devices register highs for more
fuel, lows for less. It's just a way of minimizing inputs and making the
system simpler, since there's not a lot of room in the RAM available on
the board I found for fuel maps, nor enough clock rate for lots of
calculations to compare input to a complicated fuel map.

I could probably work out inverter circuits, etc., upstream of the A/D
inputs, but it would be simpler to just input the loop result to the A/D
port on the controller board (limited number of ports available) and
program for just that, and, as said, perhaps an engine speed signal. 

Funny thing. The control system on the Lucas system is a bit of a
horror, but the metering unit itself is reliable and fairly free of
difficulties, and the nice thing is that it is fully sequential,
mechanically. 

Yeah, I know, why not go digital, entirely? But, it's an older Triumph
and I wanted it to be more stock-looking than not, and also wanted to
take it to a show in 2001, which is being held at 9800 ft. altitude....
(!) The car's younger sister (brother? niece? nephew?) is getting the
digital treatment and a turbo.

Cheers, and thanks.

-- 

Michael D. Porter
Roswell, NM
[mailto: mporter at zianet.com]

`70 GT6+ (being refurbished, slowly)
`71 GT6 Mk. III (organ donor)
`72 GT6 Mk. III (daily driver)
`64 TR4 (awaiting intensive care)
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