Joeker,
You quote :
"Since your 02 sensor is a narrow band unit, how are you able to know the A/F accurately?"
Normally, this A/F electrinic device have to calibrate first, and normaliy, this O2 sensor output voltage is 0.1v ~ 1v. Off cause, wide band O2 sensor is much much better like LM-1.But, at least, you have a ref not allow your engine to run lean,right!.
I think the Apexi turbo timer have A/F reading, not bad at all,right!
You quote :
"If not mistaken narrow band 02 sensor is only able to read stoich / near stoich a/f (0.1 ~ 1V)."
You are right on output voltage but not in A/F
The actual reading is :
0.1v - 16.5
0.2v - 15.5
0.3v - 15.2( Lean )
0.4v - 14.9
0.5v - 14.8
0.6v - 14.7( stoich )
0.7v - 13.6
0.8v - 12.6( Rich )
0.9v - 11.6
Just a ref. You can get it from web site.
Good Luck.