OK...so Shane,
For the less technical people on the list, explain this:
"Lets be clear on this - it does NOT change the A/F Ratio!" and "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
jamming the accel pedal quickly for example."
Now if you're increasing or decreasing the pulse-width, you're essentially
changing the Fuel mixture...Rich/Lean. Explain how this doesn't change the
A/F Ratio (or Mixture for better wording.)
- Bernd
-----Original Message-----
From: owner-dakota-truck@BUFFNET.NET
Subject: Re: DML: Viper/Dakota Map Modifier
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.
Thanks - Latr,
Shane
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 11:57:23 EDT