DFI, Batch Fire, and other myths

[Greg Hermann]

>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 carbon (more accurately coke, the black kind)  is residue from the
gasoline. Run av gas and it won't happen :-) !! It can also restrict
breathing pretty drastically.

Greg
>
>diy_efi at efi332.eng.ohio-state.edu wrote:
>>
>> Recent research on fuel droplet sizes has shown that injecting fuel onto a
>> closed intake valve, then letting a shot of exhaust hit it when the valve
>> opens (reversion) produces better and smaller droplets than the injector
>> itself can generate.  See the SAE Journal from a month or two ago.
>>
>> With this info, SFI could be used to insure that all the fuel is injected
>> while the valve is closed, not open.  How are the SFI systems actually
>> timed?
>>
>> Gary Derian <gderian at cybergate.net>