The old spark plugs were removed. We weren’t certain about the last time they were replaced but they looked to be cold detonating for some time and the electrodes were well worn. The proper spark gap for our 4.0L application is 0.036 but four of the old plugs were gapped at 0.050 and two were at 0.054. When removing the old plugs it’s a good idea to number them so you know which cylinder each was firing. In our case we didn’t have a felt pen handy so we laid them out on the ground in sequence as they were removed. Unfortunately, the line of old plugs was too close to the work area and were accidently kicked out of place so we weren’t able to determine where the two most worn plugs came from. Live and learn!