well you're 4.0L doesnt have a cap or a rotor, so that will save you money there, it has a coilpack. all you really need is wires and plugs. and if you want to do it with quality in mind, i'd say buy ford (motorcraft) plugs and wires.. sure they may be a little more expensive but at the end of the day, they are made for the motor, and they are made to work great with the motor.
I used to be a firm believer that NGK made the best plugs...until i put a set in my 4.0L and it had a miss with only 1500 miles on the plugs..big money waste. I dont buy anything special for it, after all its a bush truck. It has motorcraft stuff because it came with it from the factory. Except for the K&N air filter, that was just a choice because i didnt want to have to buy a new filter every time i did an oil change.
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