EFI newbiee ideas, few questions.

[nacelp]

> 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.

Don't forget about the TPS, that can be time consuming to design to get it
fail proof.
Throttle Posistion Sensor.

> As I understand it, fuel injection lets you keep the fuel ratio to a
perfect
> 14.7 mixture throughout the RPM band.

Not all the time.  Idle cruise, yes.  But it averages 14.7, it goes rich and
lean for the cat converter.  WOT (wide open throottle) is richer.

 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.

Two basic common strategies, MAF Mass Air Flow, where the air volume inhaled
is measured directly, and MAP  Manifold Absolute Pressure, where the ecm
calculates the amount of air the engine is using,, know rpm/intake vac
(short descreption).  Other less common ones available, but I'm assuming you
want to use any existing oem ecm..

> 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

Just for fine tuning really.

> 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.

There is a strategy for just using TPS, and RPM.

> So my question is, as I understand it, modern cars have all 3?

To have a closed loop system (which is about mandatory), uses the O2 sensor,
to meet todays emission standards you about have to have this.  I think if
you follow up with more reading about TBI, and TPI, some light will dawn
(lots of ink to read here).

 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).

That is what some systems use.

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.)

There is only a certain range you can work with.  Sizing injectors, and S/C
all take lots of prior research to get good results
Grumpy
>
> 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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