how do you know coil and plug are okay?

try this. swap #1 plug with #2, swap #1 coil with #3, swap #1 injector with #4, and clear code. start and check for new code. if the misfire moved, you've narrowed down the culprit. if it throws the same P0301 code again, it's compression check time.

 

how do you know coil and plug are okay?

try this. swap #1 plug with #2, swap #1 coil with #3, swap #1 injector with #4, and clear code. start and check for new code. if the misfire moved, you've narrowed down the culprit. if it throws the same P0301 code again, it's compression check time.

I did all of that, and the shop did it as well. Compression check why?

 

to rule out a bad exhaust valve or head gasket

 

Clean the MAF, check the fuel filter, run a fuel system cleaner (my personal preference is B12 Chemtool), clean grounding points, add permatex dielectric grease to contacts on the connector and inside the boot and check your plug gap to ensure it's .032.

Misfires are a pain in the butt to chase down and sometimes it's the simplest thing. Be absolutely meticulous about every detail. If none of that works i would definitely say do a compression test.

 

to rule out a bad exhaust valve or head gasket

Compression check turned out to be just fine. Going to end up doing the fuel system flush, which was done @ 78K along with fuel filter. I will reinform after further diagnostics are done. MAF was cleaned gap is good. Hopefully mechanics are not as stumped as I am.

 

Have you closely inspected the rubber boots on the coil(s)? Even a small rip/crack/tear can allow arcing...

 

Have you closely inspected the rubber boots on the coil(s)? Even a small rip/crack/tear can allow arcing...

Very good point! I've seen plug connectors that appear perfectly fine, but with close up inspection you'll notice a small black "spot" somewhere on the side of the connector. This spot is the end of of a carbon track that has been left behind after the arc through or misfire event. I used to wrap the suspect spark plug connector with aluminum foil and reinstall it in the engine for a diagnostic test. If the misfire becomes more pronounced, and you find burns on the aluminum foil, then you know it's the connector and not the plug or coil.

 

Clean grounds are a must. Even if they look good, pull them off and hit them with a wire brush imo.

 

List of possible causes for P0300-P0306 (Cylinder Misfires) out of the FSM:

Open or short engine wire

Connector connection

Vacuum hose connection
PCV hose connection
PCV valve and hose
Ignition system
Injector
Fuel pressure
Mass air flow meter
Engine coolant temp. sensor
Compression pressure

Valve clearance

Valve timing

Most of these got posted by previous posters.:tu:

 

Sooo, ran the fuel system cleaner through it, didnt work, swaping the coil packs didnt help still misfired on 1, and now misfire on 8. Compression check is good. FULL tune up 20k ago with new fuel filter, all OEM. They swapped the fuel injectors and found the misfire to move, but they seem unsure and wont guarantee that is the problem. How involved is it to replace the injectors and replace all of the seals on the others, their quote was over $500 for two injectors and replacing all the seals on the 6 other injectors, that is for 2 new OEM injectors, not refurbs. Wondering if the new fuel filter they put in 20k ago is bad and fouling out my injectors? Doubt they would tell me if it was. any thoughts or advice? I know the cylinders fire the on the 4.7 v8 1-8-4-3-6-5-7-2.

 

Back in the days, when I had AC Tundra. I had similar problem. Eventually it was fuel damper. Good luck buddy finding what causes that missfire

 

Sooo, ran the fuel system cleaner through it, didnt work, swaping the coil packs didnt help still misfired on 1, and now misfire on 8. Compression check is good. FULL tune up 20k ago with new fuel filter, all OEM. They swapped the fuel injectors and found the misfire to move, but they seem unsure and wont guarantee that is the problem. How involved is it to replace the injectors and replace all of the seals on the others, their quote was over $500 for two injectors and replacing all the seals on the 6 other injectors, that is for 2 new OEM injectors, not refurbs. Wondering if the new fuel filter they put in 20k ago is bad and fouling out my injectors? Doubt they would tell me if it was. any thoughts or advice? I know the cylinders fire the on the 4.7 v8 1-8-4-3-6-5-7-2.

I hate to recommend replacing things if they may not be bad. Maybe try to put a pressure gauge on the fuel line to test pressure. Put it after the filter first then before and you'll see if the filter is clogged and then if you're getting the right pump pressure. If neither, maybe the fuel pressure regulator. Filter and regulator are cheaper than pump or injectors.

 

Just got back from vacation, had the truck towed back to my garage and pulling all the fuel injectors out and sending them to WitchHunter Performance for refurbishing. Hopefully this solves the problem, also going to put new fuel filter on and drain gas tank. Ill keep this updated and post again when I get my Injectors back from WitchHunter.

 

I received my injectors back from WitchHunter and had one bad injector. Two of them were operating poorly. Bought a new Denso injector from RockAuto for half the price of what the dealership wanted to charge me, put them all back in (along with a new fuel filter) and... the rucks runs like new. Pretty pleased with myself. Little worried I was going to F**k something up, but runs amazing. Not really sure why all of a sudden the one fuel injector went bad and the other two started to perform poorly, but it is fixed now and thats all that I care about.