more 747 questions

[steve ravet]

Gregory A. Parmer wrote:
> 
> On Mon, 8 Jun 1998, steve ravet wrote:
> > I'm still confused.  This table lists desired A/F ratios, right?  But at
> > WOT you're not measuring A/F because you're ignoring the O2 sensor.
> > Having a table of A/F values seems to imply closed loop operation in
> > that you measure A/F, compare to what's in the table, and adjust if
> > necessary.
> 
> Steve, and others,
>   If you haven't ran across it yet, the following URL offers
> some super insight. It describes the GN system but I
> expect it will apply to all delco systems. The ECM
> learns differences required to achieve appropriate A/F
> mixtures at part throttle conditions (and sets the Block
> Learn Multipliers) and applies the same multiplier
> even when you go WOT.  In other words "open loop" is
> not entirely based on a pre-programmed map. The BLMs
> provide a learned fudge-factor.

Now I think I understand.  At WOT, the ECM looks up what A/F ratio it
needs based on rpm or whatever.  It uses a block learn value plus the
base pulse width that it thinks will give that A/F ratio.  It doesn't
bother to check the O2 sensor to verify the A/F ratio, it wouldn't give
a valid reading anyway.  I don't know why I had such a hard time with
that.

--steve


--
Steve Ravet
International Meta Systems
http://www.imes.com
steve at imes.com