And just a "heads up" I had a mechanic reverse my two upstream O2 sensor wires, they have universal plugs so no left or right difference.
Picked up the truck, ran fine then after about 4 minutes it started running poorly, and Check engine light came on, this truck had never had CEL come on before, 1994 4.0l
There was a longer uphill section on the drive home and I noticed when I went to WOT(wide open throttle) the engine smoothed out and ran fine, if I let off the gas a bit it started to run poorly.
Anyway read the codes, codes were bank1 lean, bank 2 rich ??
Cleaned MAF
Checked spark plugs
Engine ran better then after a couple of minutes started running like crap and CEL came back on
Started thinking, yes it hurt, lol.
O2 sensors are not used on Cold Start, they need to be warmed up to 600+degF to start working so computer ignores them until coolant temp gets above 140degF or so.
Computer also ignores O2 sensors at WOT, it runs a Rich mix for best power, assuming driver doesn't care about MPG just Power with foot to the floor
Only 1 wire color difference between left and right O2s, and that was it, swapped them back and all was well.
Mechanic wanted me to bring it back so he could fix it...............wonder what that would have cost me, lol.
So do O2s one at a time, or make sure you know which connector is for which side
Or if you want to sabotage someones car ....................