Not sure if it's coincidence, but my #5 misfire is gone. Engine was sounding great, still had that slight stumble at idle, but no codes. Went ahead and filled the tank with Exxon Premium and 2 cans seafoam. I ran 1 can through 1/2 a tank last week and decided to go the full Monty and do two cans with a full tank. 2 days later while cold, the CEL light came on flashing. I drove easily along and within a couple minutes light was off and truck was running awesome. Next morning, warming up, CEL flashing again.

This time the code is P0308 - Cylinder #8 misfire

Turned truck around to go home, light stopped, truck ran awesome. I cleared the code, and heading back to work it came on once more for a minute or so, then stopped. I cleared the code. For the rest of the way to work, ran great.

Coincidence? Checked plug wire, it was secure. I only do short city hops in the truck. My job is 10 minutes from home. I was trying to open her up on some stretches when the light was off, thinking maybe junk in the injectors.

Is it common for seafoam to have some side effects during cleaning?

Lastly - thinking of doing an intake line seafoam treatment. Headgasket job was done 6 months ago. New plugs, new wires. Ya'll think it worth it for a vacuum line seafoam job?

 

Well, about to do seafoam and off the bat saw that when I cleaned the iac, MAF and air intake a few days ago, the rubber intake hose came off the intake housing and was not sealing. Definitely allowing air in after the MAF. I'm sure that was not helpful.

 

Ok. Seems to be false alarm. Loose boot over intake was throwing off MAF sensor. Secured the boot, no more stumbling or misfire codes. Fingers crossed.

 

Resolved!
Resolved! Burned connector on #8. Kingsbornes less than 6 months old. Maybe too much tugging on the first install. New wires, coils, plenum gasket. Take the hood off. So much nicer. Plug wire diagram taped to window. No mistakes!

Fried #8 wire. Test light was right


Plenum open. New gasket going on.


No hood! Wonderful.


Tape your wire diagram on the windshield and check/ double check. Pulling off a wire from the wrong coil can break the wire. Do it once!

 

My tips:
Get an ignition test light. One end connects to the wire, the other to the spark plug. Good light means good spark. Good spark with still a misfire can mean it's not the wire or coil. Mine was a bad light. Bad wire.
https://www.google.com/search?q=igni...BvXRyWyZ3JM%3A
Get a plug boot puller tool. Definitely helps getting wires off plugs and off the coils.
Performance Tool Insulated Spark Plug Boot Puller, Model# W80532 | Spark Plug Tools| Northern Tool + Equipment

Get a set of wobble extensions for sockets. Definitely helps bolting/ unbolting the coil pack in the back.

Take off the hood but mark it before. Sure makes life nice.