Engine shuddering

Hello gentlemen, A few weeks ago the engine developed a shudder and CEL. 2017 2WD with 4.6 L V-8. My code reader said random misfire, and misfire on #7, and #8. The problem disappeared on its own so I didn’t address the issue until yesterday when the problem returned. The only code this time is P0308 misfire on #8.

I removed the coil pack and it’s OK visually. Swapped it with #4 to see if that would fix it. No change – still a misfire on #8. I pulled the spark plug. The plug had some carbon on the center electrode which flaked off when I blew on it. I’m guessing the loose carbon may have been due to the misfire but not sure if that’s significant. I replaced the spark plug with new Denso plug same as OEM. No change – still a misfire on #8.

The truck is not a daily driver and sits a lot in between. Mileage is only 35,000. What would be the next thing to check? Advice appreciated!

 

Whats sits alot mean? Could the gas be getting bad causing the misfire?

 

Could be dirty or bad fuel injector, fuel pump, egr valve, low compression, maybe MAF sensor...many things. It could even be a bad or loose gas cap. Least expensive thing to do is to do what you're doing. Pull things and inspect them, see if there is an obvious problem, clean them up where possible and reinstall and see if it helps at all. I'd check for a vacuum leak too. Worst thing you can do is start throwing parts at it. If you don't want to do that, paying for a live data diagnostic would be your best bet on tracking it down or find a friend with a bidirectional scanner that can decipher the data.

 

Brother-in-law had a similar misfire on his Dodge and changing the plugs didn't help. Thought it may be a clogged injector so he put a couple of cans of seafoam in the gas and low and behold it seems to have gone away after driving it a bit.

 

This, and the other posters comments about sitting and bad gas.

If it doesn’t respond to spark plug or coil pack swaps, then it’s either fuel related or deeper in the wiring/ECU. With the age and mileage, it’s way more likely it’s some weird fuel related issue and easy to try some injector/fuel system cleaner for a few bucks.

That said, it could be wiring damage from mice or something…

 

Get it down to 1/4 tank, add a can of bug 44k, give it some hard throttle and see if it clears up. If it’s not your injector, plug or coil. It’s going to be something mechanical.