I wouldn't bother warming it up. Either the plugs will tell you where your problem is or the compression test should work well enough to tell you where the problem is. You're not looking for good numbers across the board, you're just looking for the one weak hole. #6 isn't fun, but it's mostly a matter of it being hard to see. If you've got some extenders and a U joint, or the stock toolkit from under the back seat, it's not too bad to remove. The compression tester took some screwing around before it would thread, partially because it was bent, partially because I wasn't holding it at the right angle. Blow out around the plugs before removing them if you've got compressed air, they tend to accumulate dirt and rodent crap in the wells.