DFI, Batch Fire, and other myths

[Kurek, Larry]

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.
> 
>