The 258ci in our YJ was running like the timing was not quite right. The plugs looked pretty new so we checked the wires, distributor cap and rotor, and broke out the timing light. Once hooked up we found that the timing mark on the harmonic balancer was way off, and re-stabbing the distributor would not help. We guessed that either the timing chain was no good or the outer ring on the harmonic balancer had spun moving the timing mark away from true top dead center. Double boo.