ok when i first got tthe car few dayz after it ran like crap. POPING a backfireing and missin. So we found that the water pump wuz leakin so i changed evey thing. pump opti msd wires plugs the hole 9 yards. Started it up it wuz still popin is missing. Come to be it wuz a bad 02 senor. Ran fine for months. Now its doin the same damm thing again. I got a code of a left o2 senor failed. So i chaged out the 02 senor and its still doin it. Any one got ne idears

 

What was the specific code? Not all O2 sensor codes mean the sensor is bad. It might be a problem elsewhere - for example a leaky exhaust, misfires that is causing the sensor to misread the exhaust and add fuel that isn't needed, making the problem worse, and driving the long term fuel corrections to the limits, where they set the "O2 sensor lean" code.

If you have the specific code, it might indicate where the problem is, if its not actually the sensor.