L-jet

[Wouter de Waal]

Hi Andrew

I'm not quite sure if I understand what you're proposing, tell me if I read
this wrong.

You want to convert an air-flow meter (which is a flap connected to a
potentiometer (variable resistor)) to a throttle position sensor. Why?

Remember there is a difference between the ait flow and the throttle
position. Example: You're towing a caravan up a hill. Foot flat on the
floor, rpm @2500. Air flow will be 2500*engine displacement*2. On the other
hand, you're going downhill, foot off the throttle, engine revs @2500. Air
flow is now virtually zero, 'cause the engine is pumping vacuum and not air.
(What I'm saying is, in the first example, the pressure in the manifold is
equal to air pressure, in the second example it's a whole lot less. The
engine pumps the same amount of volume at the same revs, but of a much less
dense gas in the second example. Less dense = less oxygen = less fuel.

The air-flow meter measures the amount of air going into the engine. It
might happen that the throttle is fully open and the AFM only slightly open.
Some systems use alpha-n (example Fiat Uno SX in SA) where the throttle
position and revs are used to guess/compute the amount of fuel required. In
this case accelleration is a guess on top of a guess, so that errors
multiply. When you read the amount of air going into the engine directly,
accelleration is your first guess, so you can get better performance with an
air-flow type system than with alpha-n. (air-flow type, for this discussion,
is flap, manifold pressure, or hot-wire. Each of these has it's own pros and
cons, hot-wire is the most accurate but also the most expensive (read
hi-tech), reverse for manifold pressure (MAP))

OK, so if I've completely misunderstood the question, lemme know. And tell
us what you're trying to do, and to what :-)

W

--
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