Even though complex carb were mentioned--it seems that the modern car
with electronic emission controls vs. SUs is the discussion. (I came in
late can you tell) so on that note...
>The signal that they use to position the needle is outside of the throttle
>butterfly and, therefore, does not compensate for changes in manifold
>vacuum.
First, YES a signal (or measurement) is taken from the TPS (throttle
position sensor).
Second, This signal is used with many possible others: MAP (manifold
absolute pressure) sensor, MAF (mass air flow) sensor,MAT (manifold air
temp.) sensor, Knock/Noise/Detonation sensor, Vehicle speed sensor,
coolant temp. sensor...
NOTE: MAP sensor on a Throttle Body Injection system is used by the ECM
to control SPARK TIMING ONLY - after all, it just measures the vacuum!
Just like a vacuum advance distributor.
Third, fuel injectors are not position able. The needle is attached to a
solenoid which has only two states: open or closed. The amount of time
it is open or the number of times that is opened it the only thing that
can be adjusted.
>Concerning the use of oxygen sensors. My understanding is that most oxygen
>sensors are very sensitive right around stoichiometric but almost useless
>in the more rich or lean conditions.
Exactly right--as they should be. A typical GM O2 sensor gives a voltage
range of approximately .1 volts to .9 volts. The first would denote a
lean mix the later a rich mix. Considering that an O2 sensor has to be
HOT to work it can take several minutes before it even gives an output.
The ECM can and does run without it until it warms up. The point is that
a O2 sensor is just used to fine tune the mix and does not have to
register a excessively rich/lean condition. Before it would ever be
asked to perform such a feat the check engine light would light. By
using other sensors the ECM can hold the mix VERY close to ideal on it's
own. This is from personal experience using an active ECM interface on
an working vehicle. :] a very fun toy to play with!
>Am I suggesting that you dump your SU's? Not at all. The devices work
>quite well for their simplicity. The amount of money and time needed to
>replace them would never be retrieved in fuel savings. A good set of SU's
>provide acceptable drivability and isn't that what its all about?
I agree. Trying to upgrade to any type of electronic emissions would be
futile.
John Knight '73 MGB (under restoration)
"If uniqueness makes us who we are, why be like everyone else?"
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