Computer Diagnostics and Tuning Technical discussion on diagnostics and programming of the F-body computers

What tables the ECM uses to calculate a/f in different modes?

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Old Oct 30, 2003 | 05:54 AM
  #1  
InjectedSS's Avatar
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What tables the ECM uses to calculate a/f in different modes?

OK I think i've got the closed loop's figured out it's just these damn open loop tables that im really unsure of.Someone else please fill in the other blanks.

OPEN LOOP & MAF -
WOT -
PART THROTTLE -
IDLE -

OPEN LOOP & SPEED DENSITY -
WOT -
PART THROTTLE -
IDLE -

CLOSED LOOP & MAF -
WOT - PE Tables
PART THROTTLE - MAF Tables
IDLE - MAF Tables

CLOSED LOOP & SPEED DENSITY -
WOT - PE Tables
PART THROTTLE - VE Tables
IDLE - VE Tables
Old Oct 30, 2003 | 06:35 AM
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Open loop uses the table Open Loop A/F ratio x 10 (not exactly that, but it's something like that) for when the car is in open loop. I believe that is both MAF and speed density.
Old Oct 30, 2003 | 01:34 PM
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Originally posted by DOOM Master
Open loop uses the table Open Loop A/F ratio x 10 (not exactly that, but it's something like that) for when the car is in open loop. I believe that is both MAF and speed density.
So it use's the afr x 10 open loop table for everything then? part throttle, wot, and idle?
Old Oct 30, 2003 | 04:20 PM
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No, just for idle and part throttle. WOT ignores the input from the O2s and uses the %Change VS RPM WOT and %Change VS Coolant Temp WOT regardless of open or closed loop.
Old Mar 27, 2007 | 02:32 AM
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Originally Posted by DOOM Master
No, just for idle and part throttle. WOT ignores the input from the O2s and uses the %Change VS RPM WOT and %Change VS Coolant Temp WOT regardless of open or closed loop.
I have a question, what is this value being based off of? You said it uses the %Change Tables but isn't the ECM calculating off of another table as well?
Old Mar 27, 2007 | 12:28 PM
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From: Warr Acres, OK
(1 - ([# in Temp Table] + [# in RPM Table])/100)*14.7
or
14.7/(1+Number in the Cool temp table/100+ number in the RPM table /100)

Either formula will compute the 'commanded' WOT A/F. That may not be what the 'actual' WOT A/F is as measured by a wideband O2 sensor.
Old Mar 27, 2007 | 04:23 PM
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From: Ocean Springs, MS
Originally Posted by 2xLS1
(1 - ([# in Temp Table] + [# in RPM Table])/100)*14.7
or
14.7/(1+Number in the Cool temp table/100+ number in the RPM table /100)

Either formula will compute the 'commanded' WOT A/F. That may not be what the 'actual' WOT A/F is as measured by a wideband O2 sensor.
Thats good information. Regarding MAF or SD... Need an accurately calibrated MAF for correct commanded A/F or accurate VE tables for SD. I gave up trying to recalibrate the MAF the previous owner hacked up.. no sense in trying to adjust around an unknown variable. I recently decided to try my luck on calibrating the VE tables for an SD tune and so far so good..
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