1992 was officially the last 4WD 4 cylinders I believe.
This is from the History of Ford Ranger
[1992] The base engine on all 4 wheel drive Rangers was upgraded to the 140 hp. 2.9-liter V-6 with the 160 hp. 4.0-liter V-6 an option. Dropped from the 4x4 lineup was the 2.3-liter. Ford used additional galvanized steel to resist corrosion. Fog lamps were now optional on the STX Sport 4x4 Rangers. Ford discontinued the cloth headliner on the entry level S model as a way of reducing the price.
In 1993 the Rangers got heavier so I guess the power to weight ratio numbers got bad enough for Ford to not build 4cyl 4x4s unless customer wanted it.
So the 4cyls were an Option until 1997, there are 4WD 4cyl Rangers from 1993 to 1997, I think it was only an option on Regular Cab 4x4 but if a customer wanted it Ford would build it, just takes money, lol.