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couple noobiest questions: 1) why does engine rev up? 
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LQFP112 - Up with the play
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Joined: Fri Feb 01, 2013 4:18 pm
Posts: 147
Location: Jersey City, USA
Chicken or the egg question:

Why does the gasoline engine rev up when one presses the pedal? I mean, the control unit has nothing to do with that, right?
Is this all about the extra air sucked into the cylinders if I open the throttle, and consequently the bigger boom in the cylinder?

I have removed all the wires - the stock ECU does not know TP/MAP/MAF, I have implemented by own injector control with constant fuel squirts - and still, it does rev up if I open the throttle. Is that because in this particular case, with my constant width squirts, there is enough fuel to accommodate the extra air - and react with more combustion?

Is it the same deal when everything is running properly - the extra air increases the burning, the engine revs up - and the job of the ECU is just to react with proper amount of fuel and proper spark timing?

So, true/false: the extra air, mixed with the same amount of fuel as in the previous cycle, releases more energy, thus revving the engine up.

PS: if more air can produce more burning, does it mean there is always some extra fuel? Or does this all work because the same fuel can burn "better"?


Sat Mar 09, 2013 5:24 am
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Joined: Tue Jan 15, 2008 2:31 pm
Posts: 15240
Location: Home sweet home!
LOL :-)

Yep, more air = more power = more rpm.

With your simple system you've discovered that a very wide AFR range will still burn effectively.

Yes, ECUs without DBW are purely reactive.

True, likely because it was richer than stoich before.

Same fuel is burning better, but there is usually "extra" fuel to gain best torque due to incomplete combustion (goal is to use all of the O2).

One-hand Fred.

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Sat Mar 09, 2013 10:09 am
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