Turbo control in a GM ECM

[Tom Cloud]

>Now, the only speed density system I have ever worked with that has a throttle term
>to calculate base fuel (steady state) is a system that was put together strictly for racing.
>The only reason we did this was because on an individual runner intake system there
>isn't a convenient way to measure MAP.  All other systems I have worked with will ignore
>throttle unless it is changing rapidly.  You talk about turning the MAP signal into load, well


Jim ... I've not been in on this discussion, didn't even read *this*
post in its entirety -- scanned it  8^)   and this is in reply to what
I read as a statement that TPS is an unnecessary datapoint.  I'm no efi
guru, but I am opinionated  ;-)

someone on this list defined the different types of efi systems sometime
ago -- but I forget a lot ...

 - knowing the mass of the air entering the engine is what it's all
about (IMO) -- so you can determine the correct amount of go-juice
to add to the mix.  I'd say, in that regard, that rpm is a totally
useless datapoint (that's not true, I don't think, but it is in the
context of my simplistic statement above).

 - alpha-n is a system where the system uses rpm and tps only (think
that's right).  That's what the analog Holley ProJection system does.
It works fairly well, but there's a "dead" spot during part accel when
rpm hasn't caught up to the new tps setting and the mixture is lean
(this is only a problem for slow accel as there's a "Power" setting
that enrichens the mixture for WOT and an "Accelerator Pump" setting
that uses delta-TPS to richen the mixture).  The mass of the air is
deduced from pre-set values of TPS and RPM.  I'd say the main weakness
of this system is the change in air temp and barometric pressure /
altitude.

 - speed density uses TPS and MAP.  knowing the size of the opening
into the plenum (intake manifold) and the pressure diff across the
opening allows calculating / deducing the air mass entering the engine.
Adding IAT will allow it to be more correct.

 - mass air flow uses a sensor to directly measure the mass of the
air entering the engine.  Probably the most precise method, it has
drawbacks that actually made the speed density system preferable --
if you have the facilities for calibration (not the least of which
is a dyno  ;-)

 - EGO can be added to any of these systems to more precisely
control mixture -- if you really care (do you have a cat?).

Remember the caveat -- it's Monday morn, I'm getting ready to teach
a class, I don't know what I'm talking about .... etc, etc


Tom Cloud

 Clothes make the man ....  Naked people have little or no influence on society.