How could I lose 10 mpg in a week of BETTER driving?!

[Miller88]

Originally Posted by Diesel_Dave

Don't get me wrong, I'm not advocating going 20 mph on the freeway. But if we're talking strictly what's best for FE (with a manual tranny) slower is almost always better.

Instantaneous MPG on my Focus, with the cruise set at 35MPH was high 50s ... of course the engine probably wouldn't be too happy operating at 1000RPM for too long .

Edit - let me clarify - that was a PERFECTLY flat roads in the woods so there was no head/tail wind or hills. I did both directions.

[RedDevil]

I like to follow trucks and such on the highway, at a respectable distance of course. Anyone behind me will pass the truck too, so I'm not hindring anyone, and the >2 second gap I leave is big enough for anyone to exit or join the highway. Even 3 at a time, like this morning.

There's strong side wind for most of my commutes, annihilating any draft I could get from the truck. But the speed reduction alone makes it worthwhile. I do lose some time (2-3 minutes on my 22 mile commute) compared to driving at the speed limit but the driving is more relaxed, less noise. I have tinnitus, noise reduction is vital to keep my ears from ringing 24/7.

With no truck up front it does feel like hindring traffic, esp. where they upgraded the max speed to 130 kph and most of the traffic follows suit. And get less than 30 mpg from their small family cars.

[Atheria]

I'm yelling you guys, it's 42 mph. :-D

[Atheria]

Oops...damn phone...telling, not yelling.

[ali2015]

Originally Posted by RedDevil

I like to follow trucks and such on the highway, at a respectable distance of course. Anyone behind me will pass the truck too, so I'm not hindring anyone, and the >2 second gap I leave is big enough for anyone to exit or join the highway. Even 3 at a time, like this morning.

There's strong side wind for most of my commutes, annihilating any draft I could get from the truck. But the speed reduction alone makes it worthwhile. I do lose some time (2-3 minutes on my 22 mile commute) compared to driving at the speed limit but the driving is more relaxed, less noise. I have tinnitus, noise reduction is vital to keep my ears from ringing 24/7.

With no truck up front it does feel like hindring traffic, esp. where they upgraded the max speed to 130 kph and most of the traffic follows suit. And get less than 30 mpg from their small family cars.

It's hard to drive the speed limit around here,i have to do 5-10MPH over all the time or i get rear-ended by this reckless idiots on the road

[Frank Lee]

How many times have you been crashed into?

[Occasionally6]

If I can return to the OP.

Originally Posted by Atheria

Since then, I've been extra diligent about throwing the car into neutral and coasting as much as possible, etc. I was expecting to get 50 mpg on this fill-up, but nooooo....I averaged only 38.2 mpg! How can that be?! I've done the same percentage of highway vs. city driving I think, or at least approximately. I've not been gunning the car or anything. I can't figure it out and am really upset.

Atheria

I think that this is something that has been overlooked or not explained adequately:

"I've been extra diligent about throwing the car into neutral and coasting."

If you are coasting in neutral the engine is idling and consuming fuel. If you are coasting in gear sometimes it will not be.

The key is that while most of the time the engine will be driving the car, under some circumstances, such as when decelerating or coasting downhill, the car is capable of driving the engine. Under such circumstances the computer that controls the fuel flow to the engine may shut the fuel off.

Just as the engine is not capable of driving the car without a gear selected and the clutch engaged, the car cannot drive the engine without a gear selected and the clutch engaged.

Exactly when the fuel shut off occurs depends on what has been programmed into the computer but it is likely that it will only occur with the car at operating temperature, engine rpm above about 1500, and zero gas pedal. It will resume supplying fuel at a slightly lower rpm or anytime the gas pedal is depressed.

There is an easy way to tell when the shut off is occurring: look at the instantaneous consumption reading (additional stress not withstanding) and when you see "- -", the fuel cut off is active. You can adjust your driving to maximise the cut off time. You can start by leaving the car in gear!

Originally Posted by Atheria

It'll probably tell me I'm putting the car in neutral too much.

Atheria....vroom vroom!

Probably .

[ciderbarrel]

Originally Posted by Occasionally6

The key is that while most of the time the engine will be driving the car, under some circumstances, such as when decelerating or coasting downhill, the car is capable of driving the engine. Under such circumstances the computer that controls the fuel flow to the engine may shut the fuel off.

She is in the Southwest. There aren't too many steep hills out there

Were I am, I prefer clutch in coasting because the hills are steep enough that I can coast farther (and actually pick up speed) vs the engine drag where I will actually lose speed down hills. I have tried it both ways, and in my area neutral coasting is best. Ultraguage confirmed. It will jump to 100-200 MPG in neutral, but only to 80-90 MPG with engine drag.

[alvaro84]

And, if you use enutral coasting to slow down on flat, the absolute superiority of fuel cutoff is an old, busted myth. To go on zero fuel while engine braking you have to drive normally for a longer distance than if you coast in neutral, using your momentum better. The gain often outweighs the loss of the idling engine. Steep hills that let you DFCO without slowing down are mostly exceptions. There are exceptions of the exceptions, though: in ciderbarrel's case the Ultragauge confirmed that fuel cutoff doesn't happen, and it's the case with my Teresa too: she doesn't have any kind of FCD,but if you use the kill switch while engine braking the sound changes. The YARDIS is more diligent to cut off the fuel, sometimes she does even with a freezing cold engine.

[Occasionally6]

If you are slowing down anyway, so braking up to a red light or maintaining speed down hill for examples, DFCO (for Atheria, that's Deceleration Fuel Cut Off) must be better, simply because there is no fuel being consumed.

The alternative is to consume fuel idling the engine (vs one that is being motored), and because of the opportunity cost of not converting kinetic energy into electrical energy, hydraulic pressure (power steering) or cooling work (A/C).

In the case of the stoplight, you can either travel quickly up to the stop point and wait there with the engine idling, consuming fuel, or you can brake a little harder, early in the slowing down process, get into DCFCO, and "wait" with the fuel shut off and the engine accessories being driven, recovering kinetic energy, while still moving. If you do it right you will also maintain some momentum through the light when it turns green. Maintaining speed down hill simply by braking is, of course, a total energy loss.

Reading between the lines, I'm guessing that you guys are prepared to vary your speed a lot. (I'm not.) OK, if you are prepared to drop your speed way down going up hill you might gain more by avoiding the less efficient energy conversions and simply converting kinetic energy to potential energy with little loss.

How much drag the engine has with the fuel shut off will depend on the engine, what accessory load the engine is driving and on what the engine management does. Particularly with drive by wire throttle (DBW) control, but also with the way the idle control bypass air is managed with a cable throttle, the pumping loss of the engine will be minimised with DCFCO active by allowing more air into the engine than would be the case with the engine switched of and in gear. Any Exhaust Gas Recirculation (EGR) will also have an effect. You might not be getting a valid comparison if you're only cutting the injectors with a kill switch. What happens when you also open the throttle?