Just been reading a long story on the website for jeeps, where a guy had similar problems in 2012. Also a timing light that did not pick-up on one cylinder only and worked perfect on other cylinders. After all the problem was the ignition coils itself that produced a weak signal. Just enough to run the engine, not enough to run good and =barely enough to trigger the timing light. I swapped already my coils for other "used" ones of ebay, but now I am going to try a set of 3 Ohm Dyna coils an see what happens. Will post the result.