My friend and I have been debating on how the electronic limitation of
maximum speed for a car works. I'd say the engine management system
limits the amount of fuel injected, where my friend says that the
engine is turned off (which is stupid, but he's stubborn) until the
speed is reduced to the limit, and turned back on.

Is any of us right? How does it work (in particular for Audi A6 2000
model, but a general answer would be good too)?

Thanks

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Clarification of Question by thenightfox-ga on 30 Apr 2005 15:52 PDT

Thanks for the answer, but the question was for the technical part.
Like, is the amount of fuel injected reduced at some speed, do the
breaks hit, so the car moves slower... I needed to know what is
happening inside the engine when the electronic limitation of maximum
speed kicks in.

Some German cars have governors that limit their max. speed,
especially for export models to countries with speed limits (vs
Germany, where on the Autobahn  - some stretches -  there are no speed
limits.  Floor-boarding just has no further effect.
Most places it is illegal to turn off the motor while the car is
moving, especially important now when servo brakes and steering would
be affected.

That's your "general answer", no specifics, references, and not a true
GA answer, just a comment (from Germany).  :)

Drive safely!

I am interested in the technical details of the electronic limitation
of maximum speed. In other words, what is happening inside the engine
to cause a maximum speed limitation.

The electronic speedometer at max. speed is cutting off the effect of
the floor-boarded accelerator, the engine just doesn't get more gas. 
It is as though you had let up on the accelerator and were just
maintaining the speed, which at that speed (with wind resistance)
requires continuing effort.

I know my friend has a subaru outback and when the governor kicks in,
it closes the fuel line completely, and it feels very abrupt.  No fuel
"management" or anything, just complete shut off.  As with the other
comment, I don't have any references, I just know that he really knows
all about his car and I'm sure this is how it works (at least in a
subaru).

I hope he isn't trying to pass on a two lane road.
I was going to make a comment about some foreign car makers, but ...

For the technical part:  the electronics just stops passing on the
instructions from the floor-boarded accelerator pedal.
No, it does not turn of the engine (your original question).
Make a bet with your friend for the price of renting an Audi A6 2000
and have a spin.  (Or talk an Audi dealer into to letting you or the
dealer test the max. speed.)

Here's an article that discusses speed governors on trucks. I don't
understand it, but I hope someone else can use it to give an answer to
thenightfox-ga.

http://www.heavydutytrucking.com/2004/02/052a0402.asp
On-Board Speed Manager