efi555

[Peter Wales]

At 01:50 PM 1/27/96 MDT, diy_efi at coulomb.eng.ohio-state.edu wrote:

>And so it begins.  The questions, I mean.  I think I have a pretty
>good handle on how this thing would work, but I have a few
>specific questions on the circuitry.  From what I have read, the
>unit just uses pulses from the MAF to fire an injector with a
>fixed duty cycle (at least for now) every X pulses (essentially
>every so many litres of air).  Essentially a fixed pulse width,
>variable frequency system.  Later, a CPU could be added to
>modulate the injector pulse width to compensate for temperature,
>acceleration enrichment, etc.  So far so good?


Correct


>
>Ok, now for the guts of the thing.  Is the 555 run as a one shot,
>triggered by the MAF pulse, with duty cycle adjustable by the 
>control pin? 

Yes


>
>How do you determine the number of MAF pulses per injector firing?
>What kind of frequency range does the MAF put out?  


We used 12 air pulses per injection on a 2 injector 4 cylinder 330HP engine


>
>Since the system is essentially asynchronous with engine firings,
>how do you ensure that the engine does not just get a slug of fuel
>on one cylinder, then nothing on the next, etc. 


Snip
Lots of injections per revolution will elad to problems at higher RPMs due
to the approx 1.5 mS dead time on the injector. If you consider the system
as a carburettor which has an uneven fuel flow, everything will fall into
place. Yes there are cylinders which don't get their full fuel supply and
others which get too much, but the variations are so small it seems not to
bother the engine at all. For example, if in a full cycle of a V8 there are
only 7 injections but the total fuel matches the total air requirement to
maintain a correct A/F ratio, over a period of 8 cycles, all cylinders will
have had the correct amount of air and fuel.

However, if this is something which worries you, then arrange the number of
air pulse to match the number of sparks. I repeat that this system was used
in a race car to ge t330HP from an engine designed to give 200HP and it
survived quite well. It won races and was never less than 2nd.

>Lastly, some questions on the MAF sensor you recommended.  I am
>not familiar with a Starion, 

Dodge Conquest or any Mitsubishi Turbo car or even normally aspirated for
all I know.


 Some details
>on what other models, makes, and years used this MAF would be
>helpful in a junket to the local boneyard.  


>Will this thing handle
>the required airflow for a V8 making 400+ HP?
>

Yes, simply bypass the meter and measure a percentage of the air entering
the engine to get the pulse rate you want. Ours went upto 4 KHz with the
bypasses increased by 25%



Peter Wales
President Superchips Inc
Chairman Superchips Ltd        "Timing is everything"
Superchips home page with all the answers http://www.superchips.com