Using 87 in an engine designed (High Compression) for 91 can reduce MPG's when the ECU retards your ignition to control pre-ignition
(or spark knock) and reduces efficiency to burn more fuel for the same power.

 

I believe it is correct that there is no reason to use premium in a car designed to run on 87 octane. However the 2007+ MC and MCS are designed to run on premium. If you use a lower octane, the ECU retards the ignition timing to compensate. There has been much debate here as to whether this has any effect on mpg. I don't know. The engine compression ratio is high on the MCS, and even higher on the MC (since it doesn't have a turbo further compressin the air). Traditionally, high compression engines have called for high octane fuels.

The manual says to use "Super Premium/AKI 91". It also says you can use as low as 87 octane, but may experience knocking with high ambient temps or high altitudes. It goes on to warn that one should only "Top Tier Detergent Gasoline." Implying that lower price brands may contain more than "10% ethanol or other oxygenates with up to 2.8% oxygen by weight, that is, 15% MTBE or 3% methanol plus an equivalent amount of co-solvent" and damage the engine -- resulting in "unscheduled maintenance."

The injectors cannot be shut down at idle. The engine would stop. When I go down a hill near me at about 55 mph, in 6th gear, foot off the gas pedal, my ScanGagueII reads somewhere around 110-120 mpg. I believe the tach only reads upto 99.9, so you would need a ScanGaugeII to compare.

A decent pizza has protein, carbs, and vegies (at least tomato sause). I wouldn't consider it junk food unless it had too much salt, and not enough vegies. The problem with it is high calories. However, if you burn them off serving your country, I don't see a problem there.

Twinkies, dougnuts, etc. are the ones for a dad to worry about.

Wahoo!

 

No, the a/f stays at the ideal amount to keep the engine idling, if you are coasting out of gear. And if you are coasting in gear, the car's momentum keeps the motor turning, so there is no need to inject fuel, so the injectors turn off.

The injectors certainly DO shut off when you decelerate with the car in gear. Just roll down the windows at maybe 15 mph and hear for yourself.

--Dan
Mach V

 

Well said Robin. My point was that the injectors are still injecting with the car in neutral coasting or stopped, and basically shut down in gear/no throttle.
My joke on the junk food is (being in the health care business) if it doesn't make you fat and it doesn't make your cholesterol high who cares? And salt has not effect on anything with regard to your health (except in very few people with high BP and people who retain fluids-heart failure and kidney disease).
Coasting in a VW Bug is one of the most gratifying experiences of one's motoring life because they were so slow that they'd go faster in neutral than they would floored downhill. We all know that!

 

We can go over this on and on and on, and everyone can throw in whatever opinion they want to.

Technically, the injectors shut off constantly, as injectors pulse on and off to deliver fuel, but to stop pulsing entirely is a different story.

When you let off the gas, the throttle snaps closed, the oxygen sensor sees a rich signal, leans out the injectors as to not cause excessive hydrocarbon emissions.

This happens either way, coasting in or out of gear.

When you coast in neutral, the engine leans, then the PCM balances the a/f to whatever is proper at idle.

When you coast in gear, the car leans out ( roughly 18.0:1).


The car has no idea what gear you are in (In an auto, it is different). The car is using MAP signal, TMAP, TPS, FPP, O2 and other sensors to determine load and compensate for decel fuel cut.

If the car was to cut fuel entirely while coasting down in gear, it would fall on its face as if it had stalled. It is lean, but is there is still fuel being injected.


I have no experience with the DI 07+ engines yet, this is all based off of the MINI training I have recieved for Tritec MINIs.

 

---> Rick: I've done the datalogging on the R56, and on engine braking the injectors are shut off. The AFR is about 100:1 when you engine brake an R56 Cooper S. You can even hear the injectors turn off because they're very loud when they're on.

 

^^^

I just did a little research on direct injected off throttle decel fuel cut, and found this...

"A method is described for controlling the injection of fuel in a direct
injected, multi-cylinder internal combustion engine, to smooth transients
in engine output torque associated with a deceleration fuel cut-off mode
of engine operation. This is accomplished by detecting engine operating
conditions that call for the initiation of a transition associated with
the decelaration fuel cut-off engine operating mode. In response to the
detected operating conditions, a transitional period is initiated, during
which the injection of fuel into a varying portion of engine cylinders is
then interrupted. When the transitional period is associated with entry
into the deceleration fuel cut-off mode, the injection of fuel to a
progressively increasing number of cylinders is interrupted. When the
transitional period is associated with recovery from the deceleration fuel
cut-off mode, the injection of fuel to a progressively decreasing number
of engine cylinders is interrupted. The rate of entry into the fuel
cut-off mode is preferably fixed, while the rate of receovery is
determined in accordance with the position of an engine control element
for adjusting the amount of torque developed at the engine output.
Alternatively, the rate of recovery may be determined by the maximum rate
of positional change of the engine control element. "


It kills a predetermined number of injectors and that hops around. So i'm guessing on a 4, its 1-3, 2-4 until the parameters are back within limits.

It appears I was wrong in regards to the new engines! I only have experience with the Tritec engine, I haven't gotten any info on the new engines yet.





All these fancy pants new features, i'm starting to think becoming a BMW tech isn't such a good idea anymore, lol.

 

Guys, here's the deal on the injectors, decel, and idle fuel.

YES, on modern fuel-injected engines the injectors do "shut off" (meaning they inject absolutely no fuel) completely on decel when the engine RPM is above a threshold. On the Gen 1 cars, the threshold is about at 1500 RPM and you can feel a slight jerk when the fuel turns back on if you decel in gear down to this RPM. This cutoff is generally RPM based - the ECU simply starts injecting fuel again if it sees the engine getting down to near idle RPM where it knows the engine may need fuel to keep from stalling. (This is exactly what the C&D article says.)

The engine doesn't stall or "fall flat on its face" when the injectors turn off because if the RPM is above the threshold, then the wheels must be turning the engine. The engine doesn't suddenly lock up and stall when you stop feeding it gas; it just stops driving the wheels and the wheels start driving the engine.

The engine note doesn't change appreciably because the sound of the engine on decel is 99% the mechanical noise of the engine and the pumping of air through the engine, not "explosions". The tiny amount of idle fuel "explosions" wouldn't be audible anyway. (If you doubt this, turn the ignition off -- but don't lock the steering --- while you're deceling in gear some time. Nothing changes insofar as the engine noise or rate of deceleration.)

Carb'ed engines, unless they have a explicit idle cutoff system (which some did for emissions reasons in the 80's) keep giving the engine idle fuel under decel. So potentially these engines might get better mileage by deceling in neutral.

- Mark

 

This sounds like a patent application and may not represent technology in the current Mini (or any car for that matter). Because the point where idle fuel is reintroduced can cause the car to jerk, the car mfgs do look at ways to smooth the transition. What transition-smoothing mechanism is used in the Mini, I don't know, but the principle here is the same and is exactly what the C&D article says: no fuel (NONE, NADA, ZIP) is used by the engine while coasting/deceling in gear with the throttle closed.

- Mark

 

Am I understanding this correctly in thinking that it is just talking about the transition period to and from a state of deceleration?

 

hm wow, never knew that.
useful!!!

 

So if all this applies to manual transmissions, what's the story on automatics? I doubt that the wheels could ever drive the engine on an automatic.

 

Yes, they can.

At one time, it was common to 'push-start' automatics; torque converters work in both directions.

 

The problem with #1 is, you don't really coast when in gear, you decelerate. Their #1 is only true if you are going to stop or slow down in the time it would take to do it while in gear. So while I agree you will use less fuel per minute in gear, you won't get better milage than if you put it in neutral about 50% earlier and coast further before stopping or continuing on.

 

That would have to be tested to find out whether the air compression of the engine slows you down enough to compensate for the fuel burned with the engine idling. In 6th gear there may not be enough speed loss to make up for the fuel use. Since in gear is probably safer, I'll stick with not neutral coasting.

 

Thank you, that was my point too. Somehow everyone started talking about wanting to decelerate.

I would think coasting in neutral downhill (and also building momentum for the next) gives better gas mileage than driving downhill at 1/4 throttle to maintain speed against engine-braking, and then driving up the next hill beginning at a slower speed.

 

When I went to talk to my MA prior to buying my 09 I asked about gas and he said "regular is just fine to use with no problem". Then when I am taking delivery he tells me "be sure to use high octane or you will not get good mpg". Was this just the
party line" he had to say??

I used my computer to track a 125 mile round trip and it said "45.6 mpg". Can this be right?????

I see from the picture you posted that you got the "Mellow Yellow". I did as well, but the actual color of the car is more "lemon yellow" then the on line picture which is more "school bus" yellow. I was a bit disappointed. Is your really that dark a yellow?

Jim

 

Mini recommends high octane. I use 93 when available, 91 as often as possible. if your mileage seems too high check to see if you're using Imperial gallons in the settings. or don't complain

 

all right, that's it! My next tank fill I'm getting the lowest octane available to see what happens.

 

I got the 45.6 on 87.

Jim

 

Is that actual or indicated. Indicated is often at least 2 MPG higher than actual.

 

That is what the computer said, so I guess it was "indicated", still 43.6 (Converted to -2) isn't bad in my book.

Jim

 

Don't go below 87. Your results may be different in hot weather than in cold.

 

Now fess up-you were coasting in gear a lot weren't you.

 

I think it depends on how the car is programmed. I remember driving my parent's S430, and in normal mode, it goes to neutral when coasting down hill (RPM drops to idle speed). I was only able to force engine braking if I moved the lever over to manual mode.