The correct spark plug gap for a 1987 Jeep YJ depends on the engine it has. There were several engine options for that year. You
must consult your owner's manual to find the correct specification for your specific engine.
Without knowing the engine (e.g., 2.5L 4-cylinder, 4.2L 6-cylinder, etc.), it's impossible to give you the correct answer. The gap will be different for each engine.