The injectors do get shut off during deceleration - the duty cycle goes to 0. It is called Deceration fuel cut, or DFCO. This is the case on nearly all EFI systems, unless an anti-lag setup is used. The duty cycle doesnt start up again until the RPMs drop down to near idle, usually somewhere between 1200-1800RPMS depending on engine temps, RPM drop rate, etc.
From the Mitsubishi Service manual for the 3000GT, cant find any direct Evo references:
http://www.stealth316.com/2-fuelinjection.htm#j4

Did find this though - a plug in replacement ECU for Evo VII - makes use of anti-lag and DFCO using the factory sensors:
http://www.gems.co.uk/downloads/guid...0Guide%20c.pdf

 

Jesus Christ, do you realize how many people I need to apologize to now? Starting with you. I was way off on this. I have never seen Decel Fuel Cut and never even read about it. I was pretty much just stabbing with the Data Logger thing and I have never had the need to pay attention to my logs in this category. Thanks for setting me straight.

Oh, I almost forgot.

Sorry for snapping on you like I was a know-it-all.

Josh

 

The first time I hit the fuel cutoff (rev limiter) in my Evo, it felt exactly like a throttle lift -- like removing my foot completely off the accelerator pedal.

So my "butt dyno" tells me that fuel cutoff (at high RPMs) is more or less equal to completely getting out of the throttle.


A little tangent of a question here, but related... If you were to engine brake down a very long hill (like ten or twenty miles), with no fuel going into the engine, would there be any potential issues with damaging anything?

For instance, you're now causing your plugs to repeatedly spark in what is essentially just air. Your fuel pump is active but not actually pumping anything. The catalytic converter is getting "cold" air pumped through it. Certainly all of these systems are designed to handle periods of fuel cutoff, but will they be okay with going twenty minutes without any fuel? Perhaps the ECU will reactivate the injectors before anything bad can happen... I don't know.

(And I've been on some hills in the California desert where coasting in gear for twenty minutes would be realistically possible...)

 

On that link it said that it was directly related to the radiator temperature. I guess it will keep the motor firing every now and then in order to keep things nice and warm. Just to be safe, you might want to take it out of gear every few minutes and rev for a bit, just to keep things going. I would be most worried about all that backpressure possibly spinning the turbo backwards possibly and not to mention, if you went from no fuel for extended periods of time to WOT at the bottom of the hill, I could see some ways for damage to occur. It might be best to get on the go pedal from time to time in these situations.

Hell, just stand on the gas while in gear. The car handles like it is on rails. Find out if it is really drag limited or not.

Hehe.

Josh

 

Last I checked, it's only illegal to coast in neutral when going down a hill. It's a failsafe in case of brake failure or the driver passing out/dying - basically the engine will limit your top speed to whatever the max is for that gear.

 

The track is not the place to learn heal/toe downshifting. Go out in the middle of nowhere, find a nice empty highway, and learn there. You have to do it right, every time, on the track.

 

Actually, you will use less gas if you coast in gear. When you're coasting in gear, the engine is just compressing air (no fuel, no ignition), so you're not burning any gas. Coasting in neutral, you'll be the same as idling - some gas use. Check your EGTs sometime...

 

The "No engine braking for the next 3 miles" refers to heavy duty trucks with compression brakes (a.k.a. Jake brakes). They're very loud and very disruptive, and thus are banned from use in many residential areas with heavy truck traffic. Feel free to continue using your car engine to slow you down...

 

The Jake brakes sounds like an impact wrench that can't loosen or tighten anymore...only an assload louder and deeper.

I learned about DFCO reaaaal quick with the EMS. My setting still aren't tuned and man does that kill fuel economy. Very good feature to know about.

 

The max rpm and gear is not going to stop a car from accelerating going down hill. Now if a person's foot get's stuck on the gas goign up hill it will only accelerate until fuel and or ignition cut and redline.

Go find a downhill stretch of road stick it in first and let gravity do it's thing, it'll keep accelerating well past the point the motor as destroyed itself slapping it's valves against the pistons. Now if the motor locks up, that might keep you from accelerating, but now your probably going to skid of the road after accelerating to a pretty high speed and having the motor lock up the drivetrain.

If shifting and all this silliness is such a concern to so many drivers maybe the novices should stick to automatics on public roads.

 

Sounds like a ripe, juicy fart from inside the truck.

 

Good point. I guess the theory is that it'll at least slow you down a bit, rather than accelerating to terminal velocity...