Why does PCM drive car to certain A/F Ratio?
09-28-2003, 01:58 PM
#1
Why does PCM drive car to certain A/F Ratio? Noticing a couple cars that after being tuned, coem back to dyno and a/f is down to 12.0:1 Every time. loses 20 hp doing so too 
Looking in edit, theListed Stoich ratio is 14.73 or F/A .0678
Figuring out conversion to go from F/A to A/F, i dug around the Fuel Air multiplier table. When is this table used? Is the temp coolant or air temp? guesing IAT
High load (100 kpa) and warmed up its listed as 1.13 F/A in open loop. 1.13 computes to a 255 A/F by my above ratio which doesnt jive. Take the now accepted ratio of 1/30 of the edit VE table to arrive at actual VE numbers and you get 1.13/30= around .055. now if I take my earlier ratio, I arrive at 12.09 air/fuel ratio as the target. Coincidentall this coincides witht eh 12.0 soem cars seem to get driven to and where stock cars A/F ration usually is.
What do you think?
Looking in edit, theListed Stoich ratio is 14.73 or F/A .0678
Figuring out conversion to go from F/A to A/F, i dug around the Fuel Air multiplier table. When is this table used? Is the temp coolant or air temp? guesing IAT
High load (100 kpa) and warmed up its listed as 1.13 F/A in open loop. 1.13 computes to a 255 A/F by my above ratio which doesnt jive. Take the now accepted ratio of 1/30 of the edit VE table to arrive at actual VE numbers and you get 1.13/30= around .055. now if I take my earlier ratio, I arrive at 12.09 air/fuel ratio as the target. Coincidentall this coincides witht eh 12.0 soem cars seem to get driven to and where stock cars A/F ration usually is.
What do you think?
09-28-2003, 10:24 PM
#3
Re: Why does PCM drive car to certain A/F Ratio?
Noticing a couple cars that after being tuned, coem back to dyno and a/f is down to 12.0:1 Every time. loses 20 hp doing so too
Looking in edit, theListed Stoich ratio is 14.73 or F/A .0678
Figuring out conversion to go from F/A to A/F, i dug around the Fuel Air multiplier table. When is this table used? Is the temp coolant or air temp? guesing IAT
High load (100 kpa) and warmed up its listed as 1.13 F/A in open loop. 1.13 computes to a 255 A/F by my above ratio which doesnt jive. Take the now accepted ratio of 1/30 of the edit VE table to arrive at actual VE numbers and you get 1.13/30= around .055. now if I take my earlier ratio, I arrive at 12.09 air/fuel ratio as the target. Coincidentall this coincides witht eh 12.0 soem cars seem to get driven to and where stock cars A/F ration usually is.
What do you think?
Looking in edit, theListed Stoich ratio is 14.73 or F/A .0678
Figuring out conversion to go from F/A to A/F, i dug around the Fuel Air multiplier table. When is this table used? Is the temp coolant or air temp? guesing IAT
High load (100 kpa) and warmed up its listed as 1.13 F/A in open loop. 1.13 computes to a 255 A/F by my above ratio which doesnt jive. Take the now accepted ratio of 1/30 of the edit VE table to arrive at actual VE numbers and you get 1.13/30= around .055. now if I take my earlier ratio, I arrive at 12.09 air/fuel ratio as the target. Coincidentall this coincides witht eh 12.0 soem cars seem to get driven to and where stock cars A/F ration usually is.
What do you think?
I believe it's Coolant temp as 140* C = 284*F.
AFR and F/A are basically target values. I don't see the logic in applying 1/30 to the AFR or F/A targets. Maybe I'm missing something?? I don't follow...???
joel
09-29-2003, 01:55 PM
#5
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Re: Why does PCM drive car to certain A/F Ratio? I think it works by taking the AF Stoich ratio constant divided by the current F/A cell in the table.
14.73 / 1.13 = 13.03
When I get my clutch done I'm going to try and tune using my wideband to make the actual AFR match the Desired AFR (shows up in EFILive).
Eric
14.73 / 1.13 = 13.03
When I get my clutch done I'm going to try and tune using my wideband to make the actual AFR match the Desired AFR (shows up in EFILive).
Eric
