EFI newbiee ideas, few questions.

[Toby Atwater]

I just discovered this list a few days ago and I am reading everything I
can. Fascinating stuff. Just got a few questions and "what ifs"

First off my project is to "convert" a 1969 Austin Healey Sprite (1275 cc
inline 4) to Throttle Port Injection. I would hopefully keep my carbs and
just use them as throttle bodies and fabricate a piece that would fit
between the carb body and the manifold with the injector. X2 for both carbs.
I'm still in the research stage BTW.

As I understand it, fuel injection lets you keep the fuel ratio to a perfect
14.7 mixture throughout the RPM band. The injectors know how much they are
injecting therefore the only other variable is knowing how much air is going
into the engine. As I understand it, there are 3 ways to do this.

1) A "mass air flow" sensor that somehow measures the amount (and pressure)
of air coming into the engine and then in turn lets the ECU know and the ECU
calculates how much fuel the injectors need to inject.

2) An o2 sensor down the exhaust pipe inorder to tell the ECU how much more,
or less fuel in needs too inject on the next stroke to maintain the exhaust
o2 levels low therefore indirectly keeping the ratio correct to a 14.7

3) A throttle position sensor that just tells the ECU to inject more (pedal
to the metal) or less (idle) fuel into the system. This last choice seems to
be the "dumbest" method of doing it. It also depends on some kind of
variable in the ECU to know how much air is going into the engine for a
certain throttle position.

So my question is, as I understand it, modern cars have all 3? is this just
to be redundant and to MAKE SURE the mix is correct? Couldn't I just get by
with some sort of mass air flow sensor (#1). If I would ever supercharge in
the future, or I took the car too a higher altitude, I wouldn't have to
touch anything (just make sure the injectors are big enough to be able to
inject that much more fuel for SuperCharging.)

Thanks for your help. Let me know if my logic is no good either.

Toby Atwater
Santa Barbara, CA
1971 Toyota Land Cruiser
1969 Austin Healey Sprite.

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