Re: Probably the most stupid question ever.... - NOT

[Jim Cash <j.cash@xxxxxxxxxxxx>]

MaZe (?) asks:

> I own a '86 320i, and I have no experience with fuel-injected engines
> whatsoever. I've been told a lot of different ways of how to best start your
> car: just turn the key, never, ever touch the throttle until the engine runs
> is one. Another: depress the throttle slightly then start the engine. And
> yet another one: depress the throttle once fully, fully release it, then
> start the engine.
> Which way is best? Which is worst? Which is the correct way? Does one have
> to tell apart differences in cold and warm engine starting?
> 
> And addtional: how about the choke? As i understand it's a complete
> automatic choke, so i don't bother about it, it does it's job when it is
> supposed without user-intervention? Or do i have to activate it one way ot
> another? And if: how and when?


Last question first - since it helps to understand the throttle item.

There is no choke.  A choke is only on a carburettor, and you "ain't got
one anymore Dorothy".  The choke is a flap that closes across the throat
of the carb to restrict the amt. of incoming air and thereby make the
fuel mixture richer for starting. It closes according to the amount of
tension supplied by a temperature sensitive spring. (remember those
little stepped cams that flip up under the idle control setting screw -
Gees I'm old).

The way your "injected' engine does it is to use a "cold start"
injector. This pumps extra fuel into the intake manifold during the
first few seconds of cranking. It has a control unit (Thermo-Time
Switch) which cuts off the injector after a few seconds to prevent
flooding. The same switch also senses the temperate of the coolant and
does not activate the injector if the engine is already warm enough.

The only time you have to worry about this is if your engine seems to
crank for a long time before firing - in that case it is probably time
to replace that control switch.




Regarding what to do with the throttle when starting - NOTHING (at least
usually).

Normally do not touch the throttle - just fire up the ignition and the
cold start injector system will do the rest. 

BUT
It does say that if your engine is "very hot" you should hold the
throttle open part way while cranking. I read in my current manual this
may also help if the car is "very". So it appears that at temperature
extremes it may help to hold the throttle partially open while the
engine cranks.  I can understand this on a hot engine - to help lean the
mixture a bit more - but not sure why on a cold engine.  
I have never bothered in any case and never had a problem.


So all the "old" recommendations about depressing once and releasing do
not apply to an injected engine. That proceedure was used for "setting
the choke". It won't hurt if you still do it on an injected engine, but
all you are really doing is proving to yourself that the accelerator is
still attached to the throttle - because you can feel the spring
tension.


Cheers

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

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