Probably not seated well on the plug. When you push the plug wire boot over the plug, you have to make sure the wire end terminal's ring end snaps onto the spark plug. It is not connected tight until you hear the wire's end terminal snap or click onto the tip of the spark plug. If you can't hear the snap, the end of the wire may not be seating onto the spark plug tip. Push the boot back away from the spark plug wire end to investigate-the boots can get very stubborn with age-keep twisting it and pushing it till you get it moving back from end of wire. Examine the metal end tip of wire-trey to snap a spark plug down onto it now-if there is a problem with the end terminals you will see it-it may be too big to snap over the spark plug tip and hold securely, or if the ends are bent, use pliers to straighten them out. If these are aftermarket spark plug wires, the end terminals may be too small to go over the spark plug tip. You would then need a new set of spark plug wires.
I suspect you just have not pushed the wires down far enough to seat them on the plugs-push the wires onto the plugs until you hear them snap or click. Then they are seated firmly, and should not be popping off.
Answers & Comments
Probably not seated well on the plug. When you push the plug wire boot over the plug, you have to make sure the wire end terminal's ring end snaps onto the spark plug. It is not connected tight until you hear the wire's end terminal snap or click onto the tip of the spark plug. If you can't hear the snap, the end of the wire may not be seating onto the spark plug tip. Push the boot back away from the spark plug wire end to investigate-the boots can get very stubborn with age-keep twisting it and pushing it till you get it moving back from end of wire. Examine the metal end tip of wire-trey to snap a spark plug down onto it now-if there is a problem with the end terminals you will see it-it may be too big to snap over the spark plug tip and hold securely, or if the ends are bent, use pliers to straighten them out. If these are aftermarket spark plug wires, the end terminals may be too small to go over the spark plug tip. You would then need a new set of spark plug wires.
I suspect you just have not pushed the wires down far enough to seat them on the plugs-push the wires onto the plugs until you hear them snap or click. Then they are seated firmly, and should not be popping off.