O2 threshold MV for better/lean idle on LT1?
Thread Starter
TECH Regular
Joined: Aug 2005
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O2 threshold MV for better/lean idle on LT1? Does anyone know what these tables do and or need to be changed to for a modified engine to assist in idling?
I understand that the voltages are a little high for modified engines and need to be lowered for bigger camshafts etc, as your combustion chamber is less efficient and the tables for stock dont allow the O2's a good range to adjust air fuel ratio at idle etc.
It was suggested I go to 400mv for the "0" table?
These are my tables: And mods are:
396 LT1, P&P CNC heads XE230/236 camshaft 114LS, 58MMtBody LT headers.
0 579/ 597
32 522/ 557
64 548/548
96 513/513
128 495/495
I understand that the voltages are a little high for modified engines and need to be lowered for bigger camshafts etc, as your combustion chamber is less efficient and the tables for stock dont allow the O2's a good range to adjust air fuel ratio at idle etc.
It was suggested I go to 400mv for the "0" table?
These are my tables: And mods are:
396 LT1, P&P CNC heads XE230/236 camshaft 114LS, 58MMtBody LT headers.
0 579/ 597
32 522/ 557
64 548/548
96 513/513
128 495/495
I don't think they need to be changed a lot, but you can try driving
the mV thresholds lower at the lower airflow mode cells to get the
switchpoint into the indicated-lean region.
You may want to alter the mode vs airflow to cover the cam-
overlap-corrupted space better. See what your minimum idle
airflow and your (say) 2000RPM airflow readings are and make
sure there are a good number of mode cells allocated in this
range.
Then you can make with the wideband and closed loop, push
down the mV in the mode cells that surround idle airflow point
and see how the WB reading gets pushed.
You want to stay maybe 100mV or more above the minimum
O2 voltage you observe across the driving envelope. The big
swing in AFR is going to come near bottomed, the relation is
sort of asymptotic (looking at AFR vs mV curves, whole lot of
nothing between 700mV and 300mV and then it "rolls over" to
big AFR for little mV change. Same level of uselessness going
lean as going rich, for accurate but you can still tweak to a
result (whether or not that is stable, you'll have to see).
the mV thresholds lower at the lower airflow mode cells to get the
switchpoint into the indicated-lean region.
You may want to alter the mode vs airflow to cover the cam-
overlap-corrupted space better. See what your minimum idle
airflow and your (say) 2000RPM airflow readings are and make
sure there are a good number of mode cells allocated in this
range.
Then you can make with the wideband and closed loop, push
down the mV in the mode cells that surround idle airflow point
and see how the WB reading gets pushed.
You want to stay maybe 100mV or more above the minimum
O2 voltage you observe across the driving envelope. The big
swing in AFR is going to come near bottomed, the relation is
sort of asymptotic (looking at AFR vs mV curves, whole lot of
nothing between 700mV and 300mV and then it "rolls over" to
big AFR for little mV change. Same level of uselessness going
lean as going rich, for accurate but you can still tweak to a
result (whether or not that is stable, you'll have to see).
Thread Starter
TECH Regular
Joined: Aug 2005
Posts: 430
Likes: 0
Thanks for the guidance. I will see how this affects everyhting by trying to do one thing at a time. I went ahead and lowered the numbers 100mv, and it didnt idle as well as before. So, I am going 50mv up each time till I can compare graphs, just on this one threshold table thing.
There are so many things to do here, and fooling with a tune already real good is me just learning. And its amazing how little things can change allot.
Thanks again, Steve
There are so many things to do here, and fooling with a tune already real good is me just learning. And its amazing how little things can change allot.
Thanks again, Steve
