I have trouble code P0306 and not sure what I should be looking At first

[Tommylee1282]

So I bought my 04 explorer with 4.0 v6 about 4 months ago with 108k miles. I knew it needed some work but it was a great deal and I like working on explorers this is my 4th. So far I've replaced the the front shocks and struts, sway bar links l, tensioner pulley assembly, ect sensor and I the camshaft timing chain tensioner. Since I bought it, it had the timing chain rattle on startup like my 99 died from but it went away after a couple seconds. As far as problems I've had while driving on a very steep mountain highway doing 70 mph it seemed to struggle a lot to get up the hill and the service engine soon flashed and went away right after about a minute. Since that event Inreplaced the timing chain tensioner and all the rattle is gone on startup. However before I changed it occasionally while driving I'd hear a slight rattle that sounded like it was coming from the valve cover that was a seperate noise from the timing chain rattle. After changing the tensioner very rarely I'll still hear that second noise but the truck has been driving great except. Now today I was driving with the wife on a flat road and felt several times the truck struggle like it did on the hill then the service engine soon light popped on for a minute and went away. I drove it straight home and parked it. My brother has some type of obd2 scanner that bluetooths to an app on his phone. The scan showed the p0306 code. It also showed my long term full trim(1) at 3.9% and LTFT(2) at 12.5% which my brother said was a little out of the ordinary. And my STFT(2) at -4.7% no idea what that means. But back to the misfire...need some direction into where I should start checking. I'm gonna check the plugs and wires and hope it's just a bad spark plug. But if it's not a plug or wire I'm concerned that the timing chain was a little loose before I replaced the tensioner and this may have damaged a valve or injector for cylinder 6. My other thought Is there is a wire that runs over my thermostat housing that has the sensor the ect connected to it, another section runs down the thermostat housing and down behind the pulleys. If I remember from my 98 explorer this was the crankshaft position sensor wire. The first time I popped the hood and inspected everything this wire was resting on the serpentine belt and the belt had worked its way through about a third of the wire before I moved it away from the belt. Could this wire be bad and the crankshaft position sensor not giving the computer the info it needs causing a misfire? Supporting this idea my coolant temp gauge on the dash doesn't work it shakes a little when I turn the truck on but that's it. So even though the damage to the wire is after the ect sensor is the whole wire bad? Sorry for the wall of text

 

[BrooklynBay]

Check the number 6 spark plug cable first.

 

[Number4]

The LTFT(2) at 12.5 is saying that the computer had to add fuel because of unmetered air, such as a vacuum leak. Then, the STFT(1) went negative as the computer had to reduce fuel, as there was too much.

Anything under 10 is okay, but you have a swing of -4.7 to +12.5, which is 17.2, well over 10 points.