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Throttle Position vs Fuel Consumption


DOCTORBILL
07-16-2008, 12:28 PM
PLEASE - I am not looking for opinion here. Does anyone KNOW the answer?

An explanation....

I have an Audiovox Cruise Control (CC) on my '93 Geo Metro 3 cyl.

Going up a hill in 5th usually causes the CC to floor the gas pedal.

I worry that the CC solenoid will get damaged by trying to pull on the gas pedal
with full force (it is quite powerful !) when it cannot move any further.

So, when this happens, I touch the brake pedal to disengage the CC and take over with my foot.

This is when I notice something odd.

The car has reached some maximum speed that it can achieve going up the hill - it
cannot go any faster.

But I notice that letting up on the gas pedal does not make the car slow down!

Another way to say this is, there is a maximum gas pedal depression beyond which
no more power is achieved.

I think this is "The Sweet Spot" some speak of.

Question:

With the Computer Controlled Throttle Body Fuel Injector, when the car is being
taxed going up a hill, does the Fuel Injector push more or excess fuel into the TB when
the pedal is pushed PAST the "Sweet Spot"?

With the old carburetored engine, flooring the gas pedal dumped excess fuel into the Intake Manifold -
poor combustion but high power - lot of smoke out the tailpipe.

With these Computer Controlled Metros, does the computer pump only the required fuel into
the TB even if the gas pedal is to the floor?

When I go up a hill, should I hold the gas pedal at "the sweet spot" or doesn't
it matter if the pedal is past that point or not?

Another way to say it - is there a direct correlation of gas pedal position with
the amount of fuel being sprayed out by the Injector?

Does the computer "know" when more gasoline being dumped by the injector is
futile and cuts back even if I floor the gas pedal?

I don't know any other way to word this question....

Does anyone actually know the answer to this?

DoctorBill

MrPink
07-16-2008, 11:01 PM
I could give you a response from a software designer's point of view, combined with a knowledge of control electronics, but you've asked us not to do that.

-Pink

older'n'dirt
07-18-2008, 08:20 AM
Doc - From my limited experience: given that all the sensors are working properly and the ecm is functioning as it should, there will not be "excess" fuel delivered as the input from the sensors would then show a "rich" condition which will be corrected. Fuel delivery is determined by information supplied by the readings and parameters of the affected sensors working in conjunction to provide what is demanded by your foot. Air flow through the throttle body, vehicle speed, throttle position, gear selection, ambient temperature, engine temperature and a whole lot more will regulate fuel flow. If the pump/regulator/injectors delivered fuel by throttle position only, theoretically, you could drown your engine under load.

Anyone else?

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