OK so update to this. I have replaced all spark plugs with new NGK from 5* tuning and they are gaped according to what the suggested setting should be. The truck ran great for a few days and now I am back to the intermittent P0308 code for cylinder 8 misfire. The old plug gaps were out but not as bad as some that I have read. I am wondering should I swap the coil for number 8 or order a new replacement set of coils, and if so which ones? I have looked and there are several brands out there but not sure what is the best.

 

I would only replace the misfiring one. No need to replace the others if they work. Don't waste money on ones that promise stronger spark. I would stick with OEM personally.

 

Swap first to a different cyclinder to see if it is a bad coil. If the problem moves with the coil, then bad coil and replace it. If it doesn't then you have another issue.

 

OK so now i am really stumped. I swapped coils from Cylinder 8 to cylinder 2 and the issue is still on 8 cylinder. The misfire only happens when the truck is idling and sits for a little while, and it is not consistent. I do not get the misfire while I am driving down the road...only at idle with truck in park. I am planning this weekend to try and do a compression test to make sure all cylinders are good as I have read that can be an issue, however I would think if that is the issue then it would show more during driving then idling. (or am I thinking wrong) I dont have a good way of testing the injectors without going to the Stealership so I am at a standstill.....

 

Why not take it into a shop/dealer so they can tell you? I couldn't **** away that much time.

 

 

OK so latest update...After moving a coil pack and finding that didn't help the issue, still getting a cylinder 8 misfire. I decided to do a compression check, found cylinders 1-7 getting about 150 psi and cylinder 8 is getting barely 90psi. Now that I have a known compression issue with cylinder 8 i guess it is off to the dealership for them to do their checks and see what they come up with and what this is going to cost me. I bought and extended warranty when I got the truck so I am hoping that it covers whatever the issue is they find. Has anyone had a compression issue and if so what has the cause been?

 

You probably shouldn't talk too much abut your "tuner" efforts. Might void the warranty.

Detonation from too much timing advance can cause ring damage. Somebody had a similar problem to yours a short while ago and the dealer reported that a "compression test" indicated a problem and they did a whole bunch of expensive work. But they never told him what exactly they found.

A leak-down test is the common way to determine where the leak is coming from.

https://mobiloil.com/en/article/car-...-leakdown-test

 

Thank you and no I dont plan to say anything about a tuner. I plan to share what i have done in the way of troubleshooting and go from there. I will let them do the leak down test. I added a can of BG44 fuel system cleaner to my tank and am goign to finish running that through the system hoping it might just be build up on the valves or something simple.

 

90 compared to 150 plus your code isn't going to get fixed by fuel system cleaner.

Good luck. Tell them you'd like to see the actual test results. No reason they can't take a screen shot or take a picture with a phone, or write down some numbers on a piece of paper.. No reason they shouldn't tell you what they found, in detail.