I don't know of a Jeep that has a computer that doesn't have the 12 code. Mine has 12-33-55 every time I check her.

Grounds are tricky.

I give ya a raised eyebrow to the grounding via the valve cover bolt.... It's fine if you have some sort of accy on the valve cover that requires ground, but the block itself, or the cyl head is a better option.

Now, the BODY ground is different than the ENGINE ground.

Another thing to poke around a bit here is the question of are you getting crank and no fire or crank, fire, no start? Both are a pain, but quite different.

So, explain a little more here....