Ok. Under your center console you will find your computer. There will be one plug that is connected to nothing. It is a black plug. Looking at it there is two wires next to each other. Use a paper clip, piece of wire. Connect these two wires. Turn the ignition on, DO NOT start the truck. Just move to the ON postion. The check engine light will flash. The three will be 12 ( Flash *pause* flash flash)
Then it will flash the codes 3 times a piece. The last code if I remember right is a 55.
I believe it is the same. I think. Let me know if it isn't I can figure it out. Just have to go to a junkyard and find a 90 with a 4 cly.