Re: thanks and one more question

[John Greenstreet <jgreenst@motown.ge.com>]

> From quattro-owner@swiss.ans.net Wed Aug 31 12:55:29 1994
> From: David Erickson <davide@Rational.COM>
> Subject: Re: thanks and one more question
> To: quattro@swiss.ans.net
> Date: Wed, 31 Aug 1994 09:16:47 -0700 (PDT)
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> 
> > 
> >   The symptoms are basically that the engine needs about
> >   3-5 seconds of cranking before starting.  (I remember
> >   that my '83 5000s non-turbo car started up after one or two
> >   cranks)  This happens everytime the engine has been off
> >   for more than, say 1/2 hour or more.  What I mean is
> >   that once started, even if I turn off the engine right away,
> >   it will then start right away.  However, if after starting
> >   I turn off the engine and let it sit for more than 20-30 mins,
> >   the hard-to-start behavior comes back.

> Could be just the normal build-up of "varnish" which eventually causes
> the injector spray patterns to deteriorate.  Try running a few tanks
> of Chevron gas or add the Chevron fuel additive (Pro-Guard???) that has 
> Techroline in it.  Costco carries it, and it is a lot cheaper than
> an unnecessary visit to the mechanic... 
> 

What exactly is the failure mode here?  How does "varnish" figure into
this?  Does it creep up over the injectors while the car is sitting and
then go away after a few more hours?  Have you ever actually looked at
a fuel injector?  This "varnish" stuff is crap perpetrated by know-
nothing mechanics unable to admit they don't have an answer.  The
pressure in most FI systems can approach 100 psi, and at less than that
pressure the injector will clean itself.  If varnish were ever a
problem with FI, what would it have done to carburetors, which basically
function on gravity and good luck?

The only time I've had an injector problem in the 16 years that I've
owned injected cars it was caused by using STP injector "cleaner." This
stuff basically dislodges grit upstream and allows it to accumulate in
the narrowest point in the system, i.e. the injector's orfice.  This
blockage leaned-out the mixture on cylinder #3 necessitating a new
injector and a new head for $600+.  I have never used it since 1979 and
have never had any injection or other engine problems since.

It is therefore for good reason that most manufacturers do not allow
the use of this cleaner, or at least discourage it.  M-B allows the use
of Techron for cleaning dirty intake valves, but only if such a problem
exists and cannot be remedied by more agressive driving.

The bottom line is that 3-5 sec cranking on a warm engine is not
unreasonable, and could possibly be caused by temperature differentials
between the control pressure regulator and combustion chamber.  I would
check that after installing new spark plugs, if you haven't done so
already.

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John Greenstreet, Senior Engineer           (jgreenst@motown.ge.com)
Martin Marietta Government Electronic Systems    Moorestown NJ 08057
WPI Class of '75, Temple Class of '94

My new car history:
1972     1975       1978      1982       1986        1989      1992
 VW  ->   VW    ->  Audi  ->  Audi  -> Mercedes -> Mercedes -> Audi
SBug   Scirocco   Fox GTI     4000S    190E 2.3    190E 2.6    100CS

POSSLQ's* new car history:
         1978       1981       1985      1988        1990      1993
       Triumph ->  Toyota ->  Toyota  ->  VW    ->   Audi   -> Audi
       Spitfire    Tercel     Corolla   Jetta GL      80       90S

*POSSLQ = Person of Opposite Sex Sharing Living Quarters
Note: All Audis and Mercedes above were sold to friends or family.
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