I was playin with a monte ss today then check eng. light game on ran the codes 91 came up checked for vac. leaks none hooked the vac. tester up to egr its good how can I check the O2 sensor it says its running in lean mode on bank 2 thanx
i would think both banks would be lean if a primary device was at fault (i.e., fuel filter, etc).
to check the lambda, check the repair manual. it should give specs. many lambdas run from 0.1 volts to 1.0 volt in their range. normally i would check it kinda cold and then real hot and see what the voltage readings are, compared to spec.
good luck.
HISSIN50 has a point - fuel system delievery problems like bad pump or clogged filter would trip the computer to call out 41 AND 91. The possible problem cause is either an injector that isn't opening or a bad O2 sensor. I would pick the O2 sensor first.
If you have a Chilton's shop manual, you can run the cylinder balance test. It will find dead cylinders, and that is what you would have if an injector didn't open.