DFI, Batch Fire, and other myths

[andy quaas]

Wouldn't carbon hinder flow around the head of the valve?  I see that
as the problem.

Andy

---"Kurek, Larry" <lkurek at anl.gov> wrote:
>
> Ok then....explain how this works to me....
> 
> The carbon on the back of the intake absorbs fuel, so it results in
a lean
> condition? I can see this happening on startup...but what happens
when the
> carbon is saturated? It WON'T absorb any more fuel, so how does it
still
> affect fuel ratios? I doubt it is a matter of absorbing fuel when
rich, then
> releasing it when leaner...and I doubt it would have a significant
impact
> anyhow. 
> 
> I think this is one of those urban myths...or is it one of those
mechanic
> myth things? :)
> 
> Larry
> 
> 
> > 
> > On Thu, 21 Jan 1999, Shannen Durphey wrote:
> > 
> > > The sometimes less than accurate GM classes I've attended teach
that
> > > injection should occur when the intake valve is closed,and be
> > > completed immediately prior to intake valve opening.  This 
> > would make
> > > use of the heat in the head of the valve help keep fuel 
> > from pooling.
> > > This was mentioned earlier.  This might be GM's approach to sefi. 
> > > According to a service bulletin, the 3.8l engine suffers from
carbon
> > > accumulation on the back of the intake valve which significantly
> > > reduces performance.  I've seen the effects. It's very similar to
> > > losing the accelerator pump on a carb'ed engine, and the exhaust
is
> > > excessively rich.  My thought was the carbon is insulating 
> > the valve,
> > > preventing vaporization.
> > > Shannen
> > > 
> > The way I heard it [at a Mopar school] is that the carbon 
> > accumulation on
> > the back of the intake valve acts like a sponge, absorbing 
> > enough gasoline
> > that the A/F mixture is upset. IIRC, only at low and medium 
> > cruise power.
> > 
> > 
> 

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