P1391 can be the loss of either the crankshaft position sensor signal or the camshaft position sensor signal.
If this continues, you are likely to have symptoms (like the engine not starting).
Without data, all you have is an OPINION!
Past Jeeps: '49 ******, '81 Scrambler, '88 Comanche
Current Jeep: 1999 XJ Sport, bone stock, daily driver.
I work on Jeeps!!