2013 Tacoma 1GR-FE misfire with borescope picture

Hello - I bought a new to me Tacoma - it's a high mileage truck (388000 km) but mint with excellent service records. It's a project and will be my summer vehicle. It has a miss and throws codes
P219B - Bank 2 a/f ratio imbalance
P0306 - #6 misfire

I replaced all 6 spark plugs and #6 coil pack. It still has a misfire. Compression is 170 psi, cooling system pressure test @ 15 psi holds for 2 hours—no bubbling in the radiator. I still suspect a head gasket leak or possibly a failed injector harness. I also checked O2 readings and they are in spec. The truck engine runs great otherwise. I have attached a borescope picture to see if anybody can tell me if it's coolant wash or a poor fuel injector causing the pattern on top of the piston. Thanking you in advance!

 

When does the misfire occur? Idle, cold start, acceleration, all the time?

The clean area on the outside of the piston suggests that cylinder is getting oil by the rings in that area.

How does compression in that cylinder compare to the rest?

 

I'm no expert but that doesn't look like coolant wash to me.

 

this

is the fluid in there gas?
Test to see if you are getting spark on that cylinder, then move on to injector problems

 

It's most noticeable at cold start - I haven't done a compression test on any other cylinders at this point - I'm trying to figure out what's going on with #6 first. 170 is very good for this engine.

 

Being it's a cold start misfire I'd let it sit overnight with pressure on the cooling system then inspect the cylinder in question the next morning with a borescope for coolant to rule out a head gasket.

If that checks out ok then since ignition components are already new I'd move on to an injector balance test.

 

It could be a leaking injector. Even when the truck sits, it will eat off the battery and send gas down there. Perhaps check the battery voltage as well to see if something is leeching.

 

My experience is with powersport engines but whenever I saw a clean piston area it was due to fuel wash. Also normally due to bad intake design or someone's bad porting job. In this case a bad injector or even a very weak coil?