Thank you for all the help I received on this forum. First post. 2002 Ford F150XL, 4.2L V-6, 5 speed manual transmission 151K miles. Great truck. Never replaced plugs
until couple weeks ago at 149K. Engine on passenger side had a ticking sound driving me crazy for month or so. Engine ran fine with no sign of power loss, mpg did not suffer either.
Did several tests thinking it was exhaust leak. Engine running, spraying soapy water on exhaust system, blowing air from shop-vac into tailpipe etc. Did not find anything.
Every weekend I am looking for the cause and one day with engine running I notice number three plug wire on passenger side was moving from the air from the engines fan. I
grabbed the #3 wire and the ticking noise stopped. The spark plug was loose.

I did a plug change that same day and found two more plugs not as loose but loose. Three of the six plugs looked pretty bad with carbon and or ash deposits. The
other three showed obvious wear but looked normal to me. I changed the plugs with motorcraft and gapped at .054 and changed wires with motorcraft also. Changed out air filter also.

The engine performance in my opinion is less than before the change and my MPG is one to two miles per gallon less. Yesterday I changed out the passenger side oxygen sensor motorcraft
DY1401 with no problems. Tried to change out the drivers side sensor but had no luck breaking the sensor loose. Saturated the fitting and I'll try again today. Truck does seem to have more power
after a short test drive.

My main reason for posting is to make aware of the cause of my engine ticking sound to others who may think the ticking
sound is an exhaust leak because the engine performs excellent when it actually was a loose plug. I am very happy with this truck. I bought this truck used with 38K miles maybe ten years ago and has been very reliable.

Hope this may help
someone.