1988 Cherokee runs in start only dies in run

I have a 1988 jeep cherokee pioneer 4.0 with 188k mi It cranks starts 2 seconds later its dead. It will run with key in start position. I was a foriegn car mechanic specalizing in SAAB & VOLVO &VW but Ive worked on them all until 1992.I'd be happy to trade some Information as $ is kind of tight at the moment. THANKS