Oxygen Sensor going bad?

91 chevy 5.7..how will I know that my oxygen sensor is bad, and is there only one for that truck?

91 chevy 5.7..how will I know that my oxygen sensor is bad, and is there only one for that truck?
if you have a check engine lt on the code will indicate if you have a problem...why do you think this???? how many miles on O2 sensor ? if over 100,000mi just replace it as thats the life expectancy, or you risk plugging the cat converter with carbon.....91 should only have one , is this the original set up or a modified vehicle....

well the truck has over 170k on it, but the motor and tranny were both redone about 10k ago. I do not have a check engine lite on but I didn't know if I had to change it every so often as a "tune up" also..when should you change the PCV valve?

well the truck has over 170k on it, but the motor and tranny were both redone about 10k ago. I do not have a check engine lite on but I didn't know if I had to change it every so often as a "tune up" also..when should you change the PCV valve?

i replace PCV every 30,000mi approx. this is with a mix of in town /hywy driving.... when used for in town only you may have to replace more often.... i have found on my vehicles that the valve allows too much crankcase vapors to be vented the valve wears out but some experience the the PCV gets plugged and this causes the oil to leak out of engine as crankcase vapor pressures increase.....crankcase should always be slightly at vacuum....i put a piece of paper over oil fill spout,,,, with engine running paper will set over the hole held by the slight vacuum created by PCV.....