So I just bought this 2012 1500 bighorn and it has acquired a po308 code.
So naturally, I check:
Cleaned and checked fuel injector, Seems good
The coil pack, Good
The spark plugs, Good
The compression cyl 8 and 6, 120lb dry 180lb wet
Smoke tested the vacuum system, No visible leaks.
Now I'm all out of ideas.

 

Welcome to the forum!

Assuming the P0308 code comes back after you clear it, I'd suggest swapping the spark plug with another cylinder, maybe #6, and the coil with cylinder #4, then clear code. Drive it until another misfire code pops up and see if it is still reporting a misfire on #8 (suggesting injector or cylinder), #6 (suggesting spark plug issue), or #4 (suggesting coil).

Since you've already had the injector out once it sounds like, maybe you want to swap that with another cylinder as well (#2). Also, are you certain that you were checking cylinder #8 and not #7?

-Rod

 

The cylinder I was checking was the rear most toward the cab on the passenger side. This is cylinder that didn't effect idle when unplugging the injector. When I pulled the plugs they all had the same wear patterns (Dry with small/light amount of carbon build up}. I will double check with your suggestion and see were it goes.

 

Yeah, the cylinder numbering should be correct.

-Rod

 

So I swapped the coil and plugs from Cyl 8 cleared the code and went for a drive. Code finally came back on and it was still po308. I think I'm gonna have to pull the valve cove and take a look at the springs even though the compression is good. Maybe it's a flat spring but not quite broken. Still at a loss. I'm hoping its not a lifter or head seal. While I was on my drive I had my OBD2 scanner going and it was showing -20 vacuum at cruising and dropping on acceleration.

 

Well, I pulled the valve cover and the dreaded sight was in front of me cyl 8 exhaust lifter was not traveling its proper distance. wifes reaction From that, I'm gonna to assume that the roller bearing has seized and the cam lobe is flattening out. So now it's either replace the cam and lifters or replace the engine.

 

120 dry, and then 180 wet, is NOT good, that indicates the rings are going.

 

Well, it was indeed a seized lifer roller that flattened the cyl 8 exhaust cam lobe. I got the cam and all the lifters swapped out and some while I'm in there stuff done like, timing chain and spark plugs exc. after 3 weeks of weekends working on it with OEM parts. Ran great, I was super excited to get it inspected by emissions and registered. Went to emistions and their computer said it was incomplete. I have to run a drive cycle on it because the battery was disconnected so long that the computer needs reset. Did that and now I'm getting fault codes all over. Started with throttle position sensor, then the 4x4 service light, then noX sensor and cyl 1 misfire, Right now I have the truck at the dealer trying to see if they can make sense of it. On the way to the dealer about 2 miles from them, the truck went in to limp mode as I started climbing a hill and couldn't drive over 10mph. Seems to me like the computer got messed up somehow but I'm at a loss again. While working on the engine I had the battery disconnected (both terminals) and most of the wiring harness disconnected. I never touched the throttle position sensor or the 4x4 wiring but I did have to disconnect the computer terminals. Anyway, any guidance would be helpful.

One step at a time.

 

Wonder if there is a ground you missed somewhere.....

 

Well, I'm hoping for something that simple. As far as I can recall I reconnected the grounds to the heads, the right fender wall and the left fender wall. I don't recall removing any other grounds. I know I haven't given enough information to get much help here but maybe my dilemma will help somebody else going through similar problems. I'll update when the dealership finishes there diagnosis.