How is a/f calculated by the PCM?
Thread Starter
Launching!
Joined: Nov 2001
Posts: 299
Likes: 0
From: Savannah, TN
How is a/f calculated by the PCM? Looking at my autotap log after a WOT run on the street I've got:
RPM = 5652
A/F Ratio = 11.4:1
02 B1 = 845 mV
02 B2 = 880 mV
On the wideband dyno, A/F was about 12.9 at this rpm. Since then I've added 5% to the IFR table. I've got 42# injectors, longtubes, ORP (and a number of other mods).
Based on the 02s, it looks a little lean. Based on the A/F calculation from the PCM it looks rich. Which one is correct? What causes the inaccurate reading of the one that's wrong?
*I've had zero KR on a WOT run. I have had a couple spikes of 1-3 degrees below 2000 RPM but I'm thinking that this is false knock. LTRIMS averaged about -8 crusing around before I adjusted the IFR table by 5%. They now average about -4.
RPM = 5652
A/F Ratio = 11.4:1
02 B1 = 845 mV
02 B2 = 880 mV
On the wideband dyno, A/F was about 12.9 at this rpm. Since then I've added 5% to the IFR table. I've got 42# injectors, longtubes, ORP (and a number of other mods).
Based on the 02s, it looks a little lean. Based on the A/F calculation from the PCM it looks rich. Which one is correct? What causes the inaccurate reading of the one that's wrong?
*I've had zero KR on a WOT run. I have had a couple spikes of 1-3 degrees below 2000 RPM but I'm thinking that this is false knock. LTRIMS averaged about -8 crusing around before I adjusted the IFR table by 5%. They now average about -4.
Neither one is correct. The AFR from your autotap log is just the target value that GM programmed into the PCM. The GM engineers thought that 11.4 would be a good safe AFR at WOT. The mV output from your O2's at WOT is almost meaningless, and more missleading than anything else. Your wideband AFR reading of 12.9 is the actual AFR and a very good number to leave it on.
Thread Starter
Launching!
Joined: Nov 2001
Posts: 299
Likes: 0
From: Savannah, TN
Originally Posted by Cal
Neither one is correct. The AFR from your autotap log is just the target value that GM programmed into the PCM. The GM engineers thought that 11.4 would be a good safe AFR at WOT. The mV output from your O2's at WOT is almost meaningless, and more missleading than anything else. Your wideband AFR reading of 12.9 is the actual AFR and a very good number to leave it on.
Either way, I edited the timing tables as recommened by slowhawk, and edited the VE tables per ls1tuning.com. The surge and high idle have all but disappeared.
Only thing left right now is to install the fuel regulator from LPE and I'll get it back on the wideband. Then the nitrous will come
. 
