Fuel Shut Off

[Jim Cash <j.cash@xxxxxxxxxxxx>]

Jerry Cohen writes:

>  have a '98 328is and notice that when I ease off the throttle, 
> the gas consumption indicator increases up to about 40 mpg.  Then, if 
> I ease off a little more, but not all the way, it goes all the way to 
> the left (infinite ? mpg) and torque appears to decrease markedly, as 
> if the fuel injector has shut off fuel.  I  seem to remember that 
> this is a "feature."  If so, its a bit annoying in very slow traffic; 
> causes enexpected drag as the throttle is almost all the way off.   
> It also causes a similar phenomenon with the cruise control engaged 
> when going down a steep grade on the interstate, as if the breaks 
> were being applied lightly.  Is this a programmed-in feature to save 
> fuel?




Jerry 

This is a standard feature of BMW's - has been this way since at least
1982. (it worked that way on my 82 528eA).
As long as your engine RPM is above a certain level (I think about 1000
rpm), and the throttle is closed, then the fuel injectors are shut down
(infinite milage). They restart as soon as you touch the throttle, or
the RPM drops below that point.


It may be to save fuel - but it is also to provide engine braking as
soon as you take your foot off the accelerator.  

Personally, I always loved it in traffic because you have extra control,
often without having to touch the brakes.  Also useful on long downhill
sections

As you point out it also provides some braking going downhill with
cruise on - well it is just trying to keep you speed at the cruise
setting.

It has nothing to do with the consumption guage which just responds to
the use of fuel (or non use in this case) and distance travelled.


Works for me - in fact now when I get in a car that does not do this I
find I really miss it - use the brakes a lot more.


Cheers

Jim Cash
London, Ontario, Canada 
BMW CCA 102929
E39  97 540iA

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