From 1990 on through 1995 all NAS Rovers, be they Defenders, Discos or Rangies, came equipped with the On Board Diagnostic Display. It was what made the 14CUX different from the 1989 14CU engine management system. Bill, if your truck(s) didn't come with one, the previous owner either kept it or broke it and tossed it.
To the original poster, is the Check Engine Light on? If so, remove the outside plastic seat frame cover from the passenger seat.
Land Rover OBD Trouble Codes ?
With the key in the accessory II position the red LED will display the fault code(s). At least you'll have a starting point. Right now, without know if there are any codes you're pretty much operating on hunches.