Coil 8 misfire - 1986 Ford F150 SuperCab

Question edited for clarity. Full year make model in title and mis-spelling of 'misfire'.
Question moved to sub category.

The misfire code only tell you that, unfortunately it doesn't tell you why. When swapping parts to test theories, only swap one thing, one cylinder to one cylinder and only one item, the coil, the plug or the wires, not all three. What was the make of the Crankshaft Sensor? Only buy quality OEM replacements as there is a history of bad ones from Mexico and China.

Wouldn't hurt to check the wires again. This has a neat diagram.

https://www.silveradosierra.com/threads/5-3-firing-order-cylinder-diagram.734633/

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What brand of cop did you replace them with? also are you sure the injectors are ok? You may need a power balance test to determine what the root cause is

P0300 - Random multiple cylinder misfire
P0301 , 302 and 304 - Cyliners 1, 2 and 4 misfire
P0351 - Ignition coil A primary/secondary circuit malfunction
P0354 - Ignition coil D primary/secondary circuit malfunction

Faulty fuel injector.

Could be coil on spark plug or on top engine.

Sounds like a bad coil. i would swap the coils to run 2,4,6,and 8 and see if those started to misfire. If 1,3,5,7 still misfire I would do a compression test. Has the timing belt been replaced yet.

Change the spark plug wires.

get a compression test done on the engine, something may be fouling out the spark plug causing the misfire to occur.

if you can replace just the one that should be fine. most coil packs i've seen are one piece.

robert

This is a pretty common problem. I would change your valve cover gaskets. They run around ~ 50 bucks. If they are bad it will leak oil into spark plug well and cause a misfire. Very known on the 740.. Also if tune was not anytime not too long ago id change spark plugs while you at it. Then clear the computer and if you still get misfire on 8 try changing the ignition coil which is right about the cylinder with cylinder ignition coil 5. clear the computer. if you get random misfire and misfire cyclinder 5 after then its your ignition coil. parts store runs around 100 bucks