[MiniTiger]

I recently started using the instantantious fuel consumption readout as shown in the thread from "Interior and ICE"
http://www.mini2.com/forum/showthrea...&threadid=3531

to determine if gas milege is better in one gear vs another. The comsumption is shown in tenths of Liters/100KM.

One expected obseravation...
As I coasted to a stop the engine has to use fuel to keep the engine idling therefore comsumption/km would increase. This can be observed because the reading slowly increases until you come to a complete stop. As the reading gets higher and passes 999, it zeros out indicating infinite comsumption.

Anyway I noticed that during slowing down that if you leave the car in gear or down shift ( let engine slow down the car), the car actually uses less fuel. In fact the reading goes to Zero (the numbers get smaller and actually zero out) until you approach low speeds and then the consumption returns to a minimum level to sustain the idle. The reading could be at zero due to round off error and still be a very small comsumption. If you touch the gas pedal during deceleration of course comsumption starts to increase again.

I believe that when you are downshifting the computer is actually providing less fuel than normal idle and therefore better gas mileage.

I wonder if this normal with fuel injected cars with a computer or specific to the MINI because it is drive by wire and the computer can very the supply of fuel to almost nothing.

Normal cable throttle cars would have a minimum opening for fuel and would always consume fuel, even with foot off pedal and engine slowing car down.

[IMAXMINI]

It would stand to reason that the EFI ECU would cut fuel on decel; you don't need it. It uses feedback loop information from the Manifold Air Pressure sensor, Throttle Position Sensor and the Oxygen Sensor in the exahust to figure out that you're decelerating. Also note that all modern cars have a TPS or Throttle Position Sensor. The drive by wire just means that there is no mechanical connection b/n the pedal and the throttle. On deceleration, an engine can deal with "air-only" with no problem so cutting the fuel to almost nothing is no big deal since you don't need to be making any power. Most ECUs are programmed to do this for two main reasons: A.) to keep emissions down and B.) to prevent backfiring. Loads of unburned hydrocarbons are released otherwise and all that extra fuel will explode in your tailpipe if it didn't cut it on decel. In the old days (1977) they used to use a pump to add air at the exhaust ports to burn that excess fuel before leaving the manifold and destroying your muffler. I'm not sure how the new "economy meters" work but the old ones were just vacuum sensors: Decel=high vacuum and that gave you a "good" economy reading. Accel=lower vacuum and that gave you a "poor" reading. At cruising speed you had a consistent level of vaccuum so that gave you an "average" reading. Real helpful eh?
I'm sure the new ones are a little more sophisticated and actually meter the fuel through the rail or dwell time of the injectors or something to give it a more accurate reading of "fuel consumed/distance".
Nice job catching that. I have yet to be able to experiment as my MINI is still on a ship.

Motor on.

I. MINI

[sjbartnik]

Fuel reduction or total fuel cutoff on decel has been around for years on fuel-injected cars. I'd be pretty sure the MINI and most other modern cars use this technique to increase fuel economy.

Doesn't have to be throttle-by-wire to make it work, either. If you are decelerating in a car with a throttle cable, the throttle will be closed anyway.

But there are other tricks to reduce fuel delivery, such as shortening the injector pulse time or disabling the injectors altogether (probably the most commonly used method).

You don't need fuel being supplied at all if you are slowing down with the car in gear and your foot off the gas. The rotation of the wheels will keep the engine spinning as long as you keep the clutch engaged. In this situation you can have total fuel and ignition cutoff and the driver will never know.

If you are coasting in neutral then you do indeed have to use fuel to keep the engine idling.