AFR calc from Diacom data... was RE: Adding another O2 sensor

[Romans, Mark]

Steve, if Diacom shows you are commanding a 12.5 to one afr then
you are in PE, not regular closed loop.
The 15.5 (If it's 89 Code) is Hwy Fuel, a commanded leaner afr
for fuel economy.  I had mine set at 16.0 to one and got a lean
misfire. So I went back to 15.5 at speeds above 52 mph, light load
ect.
Mark
----- Original Message -----
From: "Marteney, Steven J." <smarteney at xlvision.com>
To: <gmecm at diy-efi.org>
Sent: Monday, November 06, 2000 7:14 AM
Subject: AFR calc from Diacom data... was RE: Adding another O2 sensor


> Burp! Oh, excuse me.  I think I've had too much food for thought lately.
:-)
> Hee Hee, bad joke.  I have not checked anything you mention, and have
> thought about them but the thing I am getting hung up on is predicted gas
> mileage.  I use the rpm figures to calculate the time period of one
> revolution.  From this I can get the injector duty cycle, reported PW div
by
> revolution period.  I then take the lb/hr injector rating times 8
injectors
> times the duty cycle and divide by 6 lbs for a gallon of gas.  (Is that
> right 6.0lb = 1 gal go juice?)  This gives me gallons per hour.  I then
take
> the mile per hour report and get mpg from that.  I've been suprisingly
> accurate at predicting the car's gas mileage as calculated from the
odometer
> and gas pump data.  That gave me confidence in my fuel equations.  The MAF
> is reading is a mystery to me.
>
> Now to complicate matters, I tried this method out on a friends car.  It
is
> actually my old 87 IROC 305, bone stock.  We did the same test, 70-ish mph
> on the highway.  I rated his injectors at 19lb/hr and stock fuel pressure,
> but didn't verify them.  Ran the same equations on the data and got a
> predicted mileage of 24-ish mpg.  That's right where the car ran when I
took
> it to Ohio last year.  Yet again, I think my fuel calcs are right.
>
> Now the plot sickens...  The AFR ratio calcs from the MAF reading and my
> fuel calcs for 3 data sets yielded 14.5:1, 14.8:1, and 15.5:1.  The 15.5:1
> may be invalid.  I think there is some coast down data from an I-95 off
> ramp, I'll check.  So, I'm confused.  Here's a car that is getting 24mpg
and
> says it's running at 14.7:1.  My car says 17mpg, but also says 12.5:1.
So,
> I'm trying to determine is the MAF just reading wrong and the BLMs are
> compensating and I'm really running at stoich?  Or, is the O2 sensor
reading
> false lean and I'm really running at 12.5:1 AFR all the time?
>
> Thinking out loud again, thanks!!!
> Steve (considering heated O2)
>
>
> -----Original Message-----
> From: rr [mailto:RRauscher at nni.com]
> Sent: Friday, November 03, 2000 6:21 PM
> To: gmecm at diy-efi.org
> Subject: Re: Adding another O2 sensor
>
>
> Steve,
>
> There may be some additional items to check in your quest for AFR from
> BPW. Have you checked the 'raw' bpw values to see how accurate the
> diacom software is? The other is the actual bpw itself. A bpw of 2 msec
> won't give 2 msec worth of fuel. There is the opening time to contend
with.
>
> Food for thought,
>
> BobR.
>
> Marteney, Steven J. wrote:
>
> > I kinda started drawing the conclusion that they were indeed pretty good
> > when switching.  It's a rather clever solution to get a non-ideal
product
> to
> > work, and work well.  I've been banging on the list about AFR and O2
> > inaccuracies thinking that my car is lying to me.  Still investigating.
> > Went through all my Diacom data since day 1 and the calculated AFR is
> > consistently 12.5:1 +/- 0.3.  The interesting thing is the calculated
AFR
> is
> > gradually rising as the gas mileage also rises.  I'm going to attempt
this
> > weekend to do the same highway test on my friend's bone-stock IROC (with
a
> > new MAF sensor.)
> >
> > Still playing!
> > Steve
> >
> > -----Original Message-----
> > From: Bruce Plecan [mailto:nacelp at bright.net]
> > Sent: Friday, November 03, 2000 2:33 PM
> > To: gmecm at diy-efi.org
> > Subject: Re: Adding another O2 sensor
> >
> > They are at least as fast if not more so then the oem ones.
> > Remember the ecm is shooting for a 14.7:1  AVERAGE, do it hammers things
> > real rich and lean.
> > The oem one's ******errors****** is when folks try to read them as a WB.
> > They develope cross counts at the same rate as the oems, from what I can
> > see.
> > At the Powwow we had a scope on the WB and you could see the individual
> > cylinder firings, and how they swung rich lean.
> > Bruce
> >
> > > Any comparisons to a wideband to show how GOOD they are at measuring
> > 14.7:1
> > > in switch-mode?  Are they extremely good at it, or still full of
error?
> > > Steve
> > >
> > > -----Original Message-----
> > > From: Bruce Plecan [mailto:nacelp at bright.net]
> > > Sent: Thursday, November 02, 2000 12:40 AM
> > > To: gmecm at diy-efi.org
> > > Subject: Re: Adding another O2 sensor
> > >
> > >
> > > IF, all your doing is reading side to side for 14.7:1 comparisons,
Sure
> > why
> > > not.  The oem  sensors are of a switching type.  They are not meant to
> be
> > > WBs.
> > > Bruce
> --------------------------------------------------------------------------
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