1996 GMC Sonoma

My Service Engine Code is P0171. need help in what to do to fix it. Fuem milage went from 24 to 14mpg. Have replaced both O2 sencers and cat. Eng ine compression 1 185 2 195 3 185 4 185. Fuel pressure 35-37 lbs.

P0171 Fuel Trim System Lean Bank 1
check an exhaust leak this will make the computer think it's running lean.

I have a 1994 Sonoma. After replacing many things, including the O2 sensor twice, the CPU, EGR valve, cap & rotor, the spark plugs too many times to count (each time they were replaced it was worse - I did this almost monthly, if not 2 times a month,) it seemed to be better for a week, but then it went back it it...I felt...well, like this guy-->:banghead:.

But, finally the problem was found, the fuel injector, so I agree with amac209, but if that does not work for ya (cause I do NOT know anything about codes), I think you should for SURE, check that thing.

I have a 1994 Sonoma. After replacing many things, including the O2 sensor twice, the CPU, EGR valve, cap & rotor, the spark plugs too many times to count (each time they were replaced it was worse - I did this almost monthly, if not 2 times a month,) it seemed to be better for a week, but then it went back it it...I felt...well, like this guy-->:banghead:.

But, finally the problem was found, the fuel injector, so I agree with amac209, but if that does not work for ya (cause I do NOT know anything about codes), I think you should for SURE, check that thing.
hey jezzka you said you had to replace your injectors,what was your truck running like?I have a 94 sonoma with the 4.3 and like you I have replaced the o2 sensor cap wires plugs cleaned throttle body changed oil added injector cleaner and still I only get about 19mpg.Maybe I have the same problem you had,but my truck runs fine not sluggish or anything but the plugs and the 02 sensor were fouled like a rich running engine.