Changing spark plugs and oxygen sensor on a 2003 4.0 L SOHC

[Mike'sRanger]

Helped my son change his spark plugs yesterday. His truck is at approximately 120,000 miles and was getting a code for running too lead. the plugs we changed out were the original plugs from the factory. Extremely worn down. Driver side was easy, passenger side was a bitch. Biggest problem was the middle plug on the passenger side. We aren't sure if the plug is all the way in as it was very difficult to seat the plug properly. After seating the plug and screwing it in until it stopped there were 2 or 3 threads visible on the plug. is this normal? Didn't want to force the plug and risk over tightening and possibly damaging the plug. Now there is staccato-like pst pst pst sound coming from what sounds like the passenger side just rear of the catalytic converter (could be closer to the plugs but it is hard to tell). Any advice?

Also, any tips on changing out the oxygen sensor just ahead of the catalytic converter? we are still getting a code that says it is running too lean so we are changing out the sensor today.

Thanks in advance,
Dave

 

[Uncle Gump]

Chances are the plug you had trouble with isn't seated... that is the first place you want to start.

Edit... And NO. There is nothing normal about seeing threads below the seat of plug. I wouldn't be worried about damaging the plug as much as I would be about the cylinder head.