CODE 91

[shawn13]

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

 

[5.0Droptop]

91 (R, M) System running lean - Fuel control
Could be a clogged fuel filter, bad o2 sensor, bad fp regulater. check your fuel press.

 

[HISSIN50]

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.

 

[5.0Droptop]

I played around with fuel press and a code scanner and when I got it rich and lean it read one bank only ...dunno why

 

[shawn13]

well thanx to all think Ill go out to my new home under the stang

 

[jrichker]

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.

 

[HISSIN50]

whahoo, 1800 posts and i finally made a good point. keep an eye out around 3600. i might have a gem. LOL J/K.

 

[5.0Droptop]

thats true I when i did the tests with the scanner it gave me both 41 and 91.... I forgot ...