Shouldn't the injectors be turned off completely when you're off-throttle, in gear? That would give us a theoretical fuel efficiency of infinity miles per gallon, since there are 0 gallons being delivered.

And we all know you can't divide by zero...

http://3.bp.blogspot.com/_ZTt7ivF2m-...-blog-safe.jpg

Nope.. The engine needs fuel to stay running.. If the injectors shut off then the engine would just die.. Just like a engine idling the injectors are providing fuel..

Well we all know what happens when you shut off the injectors.

That picture is funny and ironically those things are called "Glory holes". Go figure.

GIGGITY!

From my short experience with opensource tuning of my 2005 WRX, data logs would suggest that injector duty cycle is at 0% when off throttle, in gear (obviously while driving, not just sitting in a parking lot). Off throttle in neutral showed something like 4% IDC.

But prove me wrong...

I'm confused... why would anyone think the fuel injectors... would stop spraying fuel... just because the car is sitting still while running and in gear....

if the car is RUNNING... its running because fuel is being sprayed into the compression chamber VIA the injectors... using fuel from the tank. The car doesn't stay running on air. LOL...

Most I got was 421 and it filled up 12.9 gallons (60% city/40% hwy).

Ummmm really? I know glory holes suck but.


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http://www.popularmechanics.com/_mob...l-fuel-economy

Coasting in gear uses 0 fuel. Coasting in neutral uses fuel same as idling.

DFCO=Deceleration Fuel cut off. Engine and Catalyst must be at operating temperature otherwise no DFCO.

DFCO (as my understanding) was part of the OBD1->OBD2 changeover so if your vehicle is newer than 1996 is should utilize DFCO in some form or another.


Here's an OBDII easy reader:
http://groups.engin.umd.umich.edu/vi...ganesan_w2.pdf


In this case, under DFCO, the momentum of the car via the wheels/drivetrain is running the engine.

Let's see, how would the Chief say it?
Uphill, engine run make car go.
Downhill, car go make engine run.

Well, it was funny in my head.

This here showed me what has changed since I've done my tests.. Back with my old 93 grobe GT, coasting down hill with the car in 5th showed the injectors firing, when the car had the ignition shut off and the injectors stopped firing, the car would decelerate much faster and harder, the engine exhaust would change and everything.. But that car and all cars when I came to my conclusion was OBD I I didn't realize things have changed that much since I did my testing back in 03

ifsofacto....

ur telling me, that when i start my car and start coasting down hill, NO FUEL is being consumed to keep the car running? It runs cause the gear is engaged, and the car is rolling, but no fuel is pumping into the combustion chamber...

Thats what your saying? I suppose the electric spark could be turned off and the engine would still run too then...

If thats what you are saying, and ur right then cool, but it sounds like BS. I'm just sayin...

Good info to know. All I know is that when I coasted in gear with my 2005 WRX my IDC was 0% and my calculated mpgs were always better than if I coasted in neutral. That's a habit I carried over to my STI and now to the BRZ as well. I'm returning ~30-32mpg in the BRZ going mostly 70mph on my commute (90 miles round trip per day).

31 mpg for my Manual BRZ
 

I average 31 mpg suburban driving in Washington D.C. on the winter time mixture. Summertime Mixture 32 mpg. Playing in the snow 27 mpg. D.C. to Philadelphia trip never exceeding 60 mph 37 mpg. Ny to Dc just after purchase during brake in averaging 70 to 75 mph and moving between 6th and 5th gear I averaged 34.2 mpg. I have a manual transmission and I subtracted 3% for computer error.

On a 1000 mile trip with my wife and I and maximum luggage the 10 foot trunk can hold. I averaged 32.5 mpg on mostly 75 mph highway driving in the rain.