As of recently I've become more conscious of my gas mileage during everyday driving. As to alleviate this problem I've started tweaking my habits when shifting my standard transmission 4.6L '02 GT. When I know I'm going to need to slow down or stop I take the car out of gear (neutral) and coast using my brakes when necessary and popping it back into gear when acceleration is necessary. I have noticed an increase in gas mileage as predicted because idle is below 1K RPM, using less gas per second while coasting and maintaining speed.

I was telling someone I know about this when they informed me that I may actually be making my mileage worse by neutralizing the gear. They said that if you leave it in gear and engine brake (not necessarily engine braking but basically leaving it gear while braking, in other words not downshifting for the purpose of slowing the car via the engine) the engine realizes you are decelerating and does not inject fuel into the mixture while the engine continues to pump and moderately slow the car down (the slight engine braking i was talking about). By this logic, if there isn't any fuel being added to each cylinder pump you would be using zero gas while idling would use minimal.

I have no idea which is correct, all I know is idle coasting does save more gas then accelerating. Anyone care to weigh in on this idea?

 

i would say leave it in gear until you know you have to stop then put her in neutral. like you said the tach reads below 1k when coasting. ive been doing the same in my wifes gmc on 38's just trying to save some gas. and its an auto

 

i'm an old fart and i don't own a new ford so i don't know what the electronics are capable of doing.
i would think that your owners manual might say something about the proper way to approach this issue.
however, if you think about it, if the computer ..."does not inject fuel into the mixture"...,the car willdie. no fuel = no go put put.

 

The ECM will inject fuel into the intake to keep the O2 sensors heated.
I read a post here somewhere about shutting off the injectors while coasting down hills in gear with the engine turning.
http://forums.corral.net/forums/forumdisplay.php?f=339

 

the ecm does shut off the fuel injectors when coasting . its called "Coasting Fuel ShutOff " , & there are other parameters to decide when it kicks in , like rpm, speed & a few others. this aids in engine braking & engine cooling . you can clearly see this happening w/ a wideband .

 

doesnt fuel help to cool the cylinders?

 

yes . butits more efficient &will cool down a lot quicker by shutting off fuel & just having air pump through .
the ecm commands more fuel to cool down the 02 sensors , cats , & exhaust temps .

 

By coasting, you mean leaving it in gear but not accelerating, right? Or do you mean coasting as in neutral but still moving forward from the momentum of when it was accelerating.

Do the injectors use gas while the transmission is out of gear and sitting still? I'm still not sure which is better.

Again, when it's in gear but I'm not accelerating the Tach is between 1K and 1.5K, meanwhile the RPM idle at about 750 - 800 if it's out of gear.

 

yes , by coasting I mean leaving it in gear . here is a little more about coasting fuel shutoff . there are certain criteria that have to be met before the ecm will enter coasting fuel shutoff . this is how its setup from ford ,

minimumvehicle speedto enter= 25mph
minimum rpm to enter= 950
time at closed throttle to enter = 4
rpm below to turn fuel on = 800
vehicle speedbelow to turn fuel on = 3
minimum coolant temp to enter = 160


there's a few more parameters but you can see whats happening w/ these . so , say your going 25mph+ . you have to be off the accelerator for 4 seconds & then the fuel injectors will shut off.when you press in the clutch pedal & the rpm's drop to 800 the injectorsare turning back on which is sooner than if you had just left it in gear . well , in your case I would say you are probably putting it in neutral before the injectors shut off .

 

Wow that's pretty interesting. So if that is correct the ECU turns off the fuel injectors during those times,, that means there wouldn't be a noticable effect if Iturned OFF the ignition key???