Finding and bypassing the TBH leak is a good thing, but there's no way it would have caused a misfire.

It's unlikely a problem with a coil pack. DIIs use something called a wasted spark ignition system. Cylinders are paired on the coil packs. Cylinder 8 is paired with cylinder 5. If it was the coil pack, you'd likely have a misfire on #5 also.

I know it's some extra work, and you'd have to remove and replace the upper intake, but before buying new injectors you could try swapping injectors (#8 and any other one) and see if the misfire stays on 8 or moves to the swapped cylinder.

 

I second swapping the injector. I have helped a couple guys with bad sets of new injectors, moving it is the only way to validate it is or is not the injector. I recommend moving it to number 4 or 6 as they are on a different coil pack.

 

Yup - check the injectors are fully seated. I had one of the bolts holding them in come loose years after a head gasket job - sometimes it would run fine sometimes it wouldn't - all until you almost couldn't drive it. Did the same things, plugs and wires - then coils. I was about to do the drive of shame and take my truck to a professional mechanic when I thought to check that the injectors were in and down all the way.

GOOD LUCK!

 

Thanks for the advice. I'll take a look a the injectors. Fingers crossed.

 

I ran a lazy vs cheap analysis and decided to replace the coils and injectors instead of troubleshooting further.

I just wrapped up installation of the new coil packs and six* refurbished injectors. Fired it up....and took it around the block a couple times. The Beast is running great!

I'm still a tad bit hesitant. After I replaced the wires it took a ~10 miles for the P0308 to return. After repairing the coolant leak I could immediately tell it wasn't fixed. However, this time around it's running much smoother and has great power.

*I ordered a set, 8, but only received 6. Fun times. Since I was only having trouble on cylinder 8, I went ahead and installed the 6 refurbished injectors. I'll try to get a refund for the two missing injectors....or maybe have a couple around for spares / next time I pull the upper intake.