Jeep: 93 Jeep Wont Start, jeep grand cherokee, cherokee 4x4

Question
I have a 93 Jeep Grand Cherokee 4x4, 4.0L straight 6.  It started briefly yesterday morning (25 F), gave aa little backfire, then died.  I hasn't started since.  It cranks OK. The fuel pump and supply appear OK, fuel pumps out of the relief valve on the fuel rail.  Spark appears OK, screw driver in a plug wire held above the engine block.
Suggestions?
Jim

Answer
I would think it maybe the crank position sensor, it is located on the left side of the bellhousing at the top.  It may not be giving the right signal causing it to fire at the wrong time.  It could have possibly jumped time or broke the camshaft, but not likely.  Hope i could help.