"Bernd D. Ratsch" wrote:
> I've already been working with Sean Roe on this and in answer to your
> questions:
>
> Yes, it can change the A/F Ratio (+/- 20% PW)
Lets be clear on this - it does NOT change the A/F Ratio! What it changes is
the signal that the PCM is getting from the MAP sensor. Nothing is changing
the signal from the oxygen sensor. It is still a 14.7 to 1 oxygen sensor. The
PCMs main strategy (closed loop) is to hover around 14.7 to 1 Air/Fuel ratio.
It will do this with or without the VEC1 being hooked up. I would love someone
to be able to prove otherwise but only the high-doller aftermarket EFI vendors
can actually allow you to dial in say a 12.5 to 1 A/F ratio and run around in
closed-loop around 12.5 to 1 (best power).
So just what does it do? Well it is only wired into the MAP sensor circuit.
The A/F ratio MONITOR is just that - a gauge - nothing more. How can just
modifying the MAPs output change PW (pulsewidth) and timing? Its because
looking up PWs and degrees timing advance/retard in a table doesn't occur ONLY
during open loop. These pre-programmed values (either table-driven or even
calculated on-the-fly) come into play during closed-loop also. They are
related mostly to driveability - think of a carbs pump shot for example. Our
PCMs supply a "pump-shot" also based on load. Since load is measured using the
MAP sensor (among others) - this is how the VEC1 can change PW and timing.
During these transients, MAP is a major contributor to the table lookup or
computation as the PCM determines the optimum amount of PW and timing to add so
you don't feel a bog while jammin the accel pedal quickly for example. Now
when that 14.7 to 1 oxygen sensor picks up on that pump shot (by reading rich),
the PCM will back out the PW until it goes below 0.45V (14.7 to 1). So you
haven't really changed the A/F Ratio - you just got a bigger or smaller
momentary "pump-shot". I used the "pump-shot" as an example because most
people can relate to that. There are many of these driveability transients - I
would guess even more than 10 or so - that are also largely controlled by the
MAP sensor output.
>
> Yes, it can change the timing (+/- 11 Degrees)
This I believe for sure! Again, based on the momentary transients - not the
curve itself.
>
> and it hooks up to your existing O2 but without the common voltage bleed as
> with the other A/F Meters.
Give us more info on what you mean by "without the common voltage bleed as with
other A/F Meters"??? I haven't seen one yet as sensitive or with as much
resolution as my Autometer A/F gauge.
Thanks - Latr,
Shane
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 11:57:23 EDT