92' W150 runs normal when cold and runs rough once warmed up. Hooked up my OTC 4000 and looked at what the computer is doing. Once the truck gets warmed up it stays LEAN all the time. O2 values start out at .52 when truck is cold. Once the truck is running the O2 values never go above .50. Once warmed up they mostly stay around .30. I am fairly sure they are supposed to bounce around over and under .50 once warmed up. AFF stays at +%49 once warmed up. Can smell the gas pouring out the tailpipe. So it looks like the computer thinks the truck is running lean so it is dumping gas in the cylinders. Sounds like it needs a new O2 sensor but just looking for confirmation or if there might be something else.

 

could be the o2 sensor especially if is has a 318 in the truck. when the plenum gasket starts leaking your engine starts burning oil and your o2 sensor starts getting fouled up. if you are going to replace it you should use a NTK brand o2 sensor. they are OEM.

 

It was the o2 sensor. Took your advice and got the NTK brand. Truck hasn't run this smooth in a long time. Heated the bung with a torch and used (and broke) a Snap On o2 tool. Ended up cutting out the exhaust. Replaced the header bolts with stainless and had a stainless sleeve welded in where the factory joint was. Problem solved for next time.

 

i guess i forgot to tell you that the best way to remove the old o2 sensor is using a pipe wrench. after being in the same place for 20+ years they definitely won't want to move.

 

That's for sure. Soaked it with PB Blaster more than a few times. Heated the bung till it was almost red. And had a Snap On o2 socket and Snap On 2 ft breaker bar. Breaker bar would not budge until the socket adapter snapped. It may have been the original o2. I've had the truck for 12 years and pretty sure my father never changed it before me.

 

well most people don't replace the o2 sensor at the scheduled maintenance interval like they are suppose to and wait until they stop working properly. this can result in a vehicle getting bad gas mileage or having the engine run poorly.