LSkrabut

This past weekend, driving in rather mountainous roads going downhill, I was downshifting using the paddles to keep my speed down instead of using the brakes in my E250 (Diesel).

Why watching the Command display – Fuel Consumption Indicator, usually after a few minutes or more, the fuel usage indicated 80MPG or better as expected. Now comes the interesting part, intermittently the fuel usage indicated “0”. The only photo I took is attached, but it happen randomly and I wasn’t able to pinpoint when or why, other than only when I started to use manual mode in the transmission and goingdownhill without any throttle applied for periods of time.

BTW, it never happen before that I noticed, not that I ever really view Fuel Consumption in mountains and manual transmission mode at the same time going down rather long hills - gliding mostly. I currently have over 41K miles on the motor and I feel it is running beautifully. No hiccups or any other sort of issues. Myself I feel this is some sort of Command/ECU issue showing its hand.

looney100

Maybe your Economy was too high to be displayed.

mikemargolis

No comment on the fuel chart, but only to say:

I set the cruise control going down long hills, and this car keeps you at the set speed, whether by engine braking or using the wheel brakes if needed.

How awesome is that?

looney100

I was pretty impressed when I first saw that too - and it's a pretty tight tolerance. It uses the brakes.
I don't know if it's an evolution of the technology or simply my movement into higher priced vehicles, but anything I owned prior to 2009 wouldn't brake at all during cruise. Our 2009 Acura would downshift and attempt to use engine breaking to slow you, but on steep hills it wasn't effective and you could find yourself going 30 km/h faster then you set the cruise. Our E-classes engage the brakes to keep you spot-on.

Arrie

Well, there are some old cars that did hold speed going down hills. I had a 1985 Lincoln Mark VII LSC. It had butterfly valve in the exhaust pipe to hold the speed when going down hills with the cruise control on.

And it also had the air pump that pumped air in the exhaust manifold with the car idling. I read this was a way to lean the exhaust emission test results so what is going on with VW at the moment may not be that new "behaviour" at all.

LSkrabut

Update:


This will occur in any of the transmissions modes, Manual, E or S.


I was able to determine this past weekend, going down the same mountain road, this will occur anytime no throttle is applied during one of the minutes cycles being displayed the fuel consumption indicator will register nothing.


Now this is a somewhat rare occurrence, got to have a rather long downhill drive where the throttle is not touch or increase from a completely closed status.

rediesel

Mine not only holds the speed going downhill it also slows to the flow of traffic - I love distronic.

Shadow5501

Fuel to the engine is completely shut off when coasting. All modern cars have this feature, both gasoline and diesel. It's called DFCO - deceleration fuel cutout.


I'm guessing you coasted for a full minute down the mountain. Hence no fuel at all was consumed during the measurement period for that bar in the graph. Fuel usage is the denominator in the fuel economy equation. But you can't divide by zero, hence the lack of a bar in the graph.


Most cars I've driven just go to 99MPG and call it done. But Mercedes always seems to do things a little bit different.