Clay Cooke wrote:
> > You can run the 24's if you want, but remember that your computer is
> > calibrated to run at a 19# flow rate. So the computer will think it's running
> > a certain amount of fuel, but it's actually running more. Now with the ram
> > air you might get better a/f ratio at speed, but I think you'll still run
> > rich at idle. If you're going to upgrade, don't go 30's.
>
> Actually at idle he should be fine, truck is running off the O2 sensor at
> anything but WOT. The computer will adjust the pulse width of the
> injectors at anything bu WOT for the correct A/F ratio, but at WOT the
> computer uses preset timing on the injectors so you will get more fuel
> then, which is usually when you need it most anyway...
This is mostly correct from my understanding. The computer also ignores the O2
sensor during the first few minutes of operation on a cold start. This is due to
the time it takes for the O2 sensor to provide valid information (warm-it-up to
operating temp). The O2 sensor is a heated type (has built-in heater) to shorten
that period. You can watch this behavior using an Air/Fuel meter. Ever notice the
faint white looking smoke out the tailpipe when cold? During these first few
minutes the computer is in open loop mode reading built-in table data for injector
pulsewidth. The factory uses a overly rich mixture here for cold-start enrichment
as well as to somewhat compensate for potential mods. Since there is no "feedback"
during open loop mode, the computer can't "close-the-loop" and actually KNOW what
the current A/F ratio is. Therefore, the factory wants to make sure it doesnt go
lean during the time it isn't verifying actual A/F ratio. Hence the overly
richness that is built-in to those tables (2 tables probably - 1 for cold - 1 for
WOT). This is two ways (cold rich table & WOT rich table) the computer attempts to
compensate for potential mods. Just about the time the O2 sensor gets excited
(this is known to the computer due to a bias voltage it uses with a comparator) the
smoke clears up and we are in closed-loop.
A/F meters are cool!
Anybody agree? 8-)
Latr,
Shane
-- '96 IndyRam w/lots of mods (mine) '96 IndyRam w/lots of options (wifes) - also a numbered (#142) "Track Truck" '74 Triple-Black Dodge Challenger Rallye 360 home-brew EFI R&D vehicle '68 Black Corvette Convertible 427 (For Sale)
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