Originally Posted by jgorm
Why is there a difference on plugs if you have a distributor or not?
Because newer DIS (distributorless ignition system) ignitions require both sides of the gap be made from the same material due to how they fire the plugs. The APP-985 and 7034 have platinum on both sides of the gap, AP-985 and 3034 only have it on one side of the gap. Installing the AP-985, 3034, or similar technology plugs into newer DIS equipped 4.0L engines will eventually cause misfiring or other hard to diagnose engine idle/run problems.
Jeep issued a TSB about that particular problem to alert their techs to remove that type of plug when that problem is encountered. DIS engines can only run conventional, double-tipped platinums like the APP-985 or 7034, or iridium like the Autolite XP-785. The only type of plug DIS engines don't run well with are single-tipped plugs like the AP985 and 3034.
Older style distributor-equipped engines can run either/any type plug without problem. It's just that the APP-985 and 7034 plugs cost more without any benefit for the older non-DIS style engines.