How do AICs work?

[Daniel Houlton]

soren wrote:
> 
> >If I need to intercept and modify the MAF signal anyways, then I'd much
> >rather swap to larger injectors than run the rising rate FPR or plumb in
> >additional injectors.  It's much cleaner I think, doesn't have any bad
> >sides that I can see (so long as I don't go so big it won't idle) and
> >it's much more stealthy.  I'll have a much better chance of sliding this
> >whole thing by the smog police if I don't have a huge regulator or extra
> >fuel lines and injectors running everywhere.
> >
> >Any insight is appreciated.
> 
> 
>     I definitely agree that larger injectors are the way to go depending on
> your budget.  The lack of extra plumbing is definitely a plus.  However, if
> the ECM is reacting to the extra boost and going to 100% duty cycle on the
> stock injectors but cannot react to the change in fuel mixture caused by an
> additional injector (because it is in open loop), how could it react to the
> change in fuel mixture caused by the larger injectors when the ECM commanded
> 100% d.c.(again in open-loop)?  It appears to me as if they would be similar
> in actual function.
> 
> Soren Rounds


Regardless of how the extra fuel is added, the idea is to keep the ECM from 
commanding 100% d.c. by intercepting the MAF signal, changing (reducing) it,
and then passing it on to the ECM.  How much to reduce it is the tricky part
as the MAF output is not linear to the airflow through it.

In the case of the addition injector or higher fuel pressure, I'd have to 
figure houw much to reduce the MAF signal based on how much extra fuel the 
higher pressure or extra injectors will dump.  i.e. if the extra injectors are
dumping 30% of the total fuel, the MAF signal to the ECM would have to be 
reduced enough such that the ECM injects 30% less fuel.

With larger injectors that flow say 50% more fuel than stock, the MAF signal
would need to be reduced enough so that the ECM would inject only 66% of the
fuel it would of from the un-modified signal.

When it's in open-loop WOT, it reads the MAF directly and squirts an appropriate
amount of fuel.  The extra fuel from having larger injectors is offset by a
shorter pulsewidth (and therefore duty cycle) commanded by the ECM from seeing
a lower signal from the MAF.


--Dan