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Old 03-18-2012, 11:53 PM   #25
AMMO-Duke
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Since this thread started out with a Duratec, all of my comments below pertain to the Duratec. I assume the Zetec is not much different, but I have never worked on one.

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Let's work out the logic: If the PCM is told it's running a few (and that's VERY important, if you eff-up your math and get it wrong by twenty degrees = not good) degrees cooler than it's been programmed to run 'optimally', it does what?! adds air and fuel to warm it all up; the net result is more power and a slight loss of mpgs.
I agree...lets work out the logic!
1-The PCM/ECU is programmed to react to the actual ECT and ACT by adding/subtracting timing.
2-It does not add air or fuel based on temperature. At WOT, fuel is added based on the mass of air the MAF sensor detects, not ECT. If the actual air temp entering the engine is lowered, the MAF sensor will detect a greater mass and will adjust fuel to match this amount of actual air.

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adds air and fuel to warm it all up
It simply does not work this way. The ECU does not have a target temperature and does not add air or fuel to change anything. If you trick the ECU into thinking the ECT or ACT is colder, all it will do is add timing. The problem is you dont know how close you already are to detonation. You might add a few degrees and be fine, or you might activate the knock sensor which can pull more timing than you added, taking a step backwards. Bottom line: Without careful datalogging, you really dont know what is happening!

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the net result is more power and a slight loss of mpgs
I am almost at a loss for words. I assume you are thinking that you added more fuel and this is where your power gains are from. This is kind of irrelevant, because what you are doing will not change the A/F ratio. For arguments sake, lets say you did add more fuel. How could you say you will gain power when you did not know the A/F ratio to begin with. Maybe it was too rich to begin with. How many stock engines have you datalogged? I datalogged mine when it was 100% stock and the A/F ratio at WOT was so rich it went off the range of my wideband at 10:1! If it was any richer, I think it would have died. Most naturally aspirated engines make their peak power around 13:1 A/F ratio. Chances are that your stock ECU is already running richer than this.

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based on it, and other sensors, the computer reacts to change a/f ratio to suit for the optimal setting in the stock maps
Once again, the ECU does not adjust A/F ratio based on ECT

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a cold engine creates more NOX and other pollutants, Ford engineered efficiency into the system for emissions sake, not power
You are correct in the above statement as it pertains to idle and part throttle cruising(Closed Loop Operation). Once you go WOT(Open Loop Operation) everything changes. The ECU is not programmed for emissions at WOT, it is programmed to run rich enough to be safe and is most likely too rich for max power to begin with.
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