2012 100k Miles with P0305 Cylinder 5 Misfire

[2012MichLSTahoe]

I hope its okay to start a new thread. I know there are more than enough regarding chasing down misfires. I've own my 2012 for 3-4 months now and the forums are an amazing resource. I wouldn't be asking, but I am not sure what to try next or bite the bullet and take it to the mechanic I know. I tried ruling out the easy things.

My Tahoe has had a very slight shudder in the idle since I bought it. Reminded me of worn engine mounts. Anyway about a week ago the engine light came on. Returns P0305, I tried ruling out all the easy things..... plugs, wires, coil pack by swapping 5 and 3. no change. Pulled the plug on 5 and it idles worse but rpms are about the same. Today, I put 15 gallons of E85 and fuel injector cleaner in it (as a hail mary).

When reset takes a couple days to come on. OBD2 test gives me about 200 misfires at idle in 10-15 minutes, doesn't misfire under load/while driving.

Not sure where to move from here....

1. go through a few tanks of cleaner
2. do a compression test
3. look for a vacuum leak (not 100% sure how to)
4. start to get into pulling and testing the injectors, electrical/psi/spray

Any help would be much appreciated!

 

[2012MichLSTahoe]

Hoping pictures help.... (maybe at least for some attention)


Bought a grocery getter, pulled the running board, added Ram wheels and new tires on, EONON head unit with OBD, corrected the paint, love it soo far.

Oh and Im getting about 15 mpg highway (80mph/no trailer), maybe related to the misfire.

Run it about 160 miles to the cabin in Central/Northern Michigan. Tow a couple smaller Kubotas (B&L) around from time to time.

Thanks!

 

[solli5pack]

Any unnatural noises coming from the engine while it's running? Maybe something that sounds like an exhaust leak but is actually a failing lifter. There are specific procedures to test and rule out everything else like spark, fuel and air and when you've confidently ruled them out it usually leads to an internal issue. Pretty sure cyl 5 is a non afm lifter but it can still fail and so can the tray that holds it. I had one fail on my Yukon and it sounded exactly like an exhaust leak at the manifold.