I have a 1989 Ford Ranger XLT with the 2.9L V6 and an A4LD Automatic Transmission.
Bought it 6 months ago, and it idled very rough and chugged once it decelerated. I changed out the elbow connections coming off of the fuel injector that were very loose, charged the AC (which still does not blow cold due to possibly the electrical wires), and swapped out the PCV Valve grommet so that it was sealed off. I also changed the muffler and tailpipes, which were damaged.
Drove like a dream for a couple of days, then got to where it would reverse, drive down a block, then if I stopped and went to accelerate again, revved up as in neutral. I would cycle the shifter on the column through the gears and it would catch and drive like normal. After a couple more days, it started to drop into neutral at multiple stops in a row and I took it straight home to the garage.
I had to cut off the old catalytic converter to get to the vacuum modulator. I put on a new vacuum modulator and catalytic converter. The Ranger would engage in all of the gears when shifting on the column, reverse and drive, but would not automatically shift from first to second gear when accelerating. I could manually shift it on the column, but could not get it to automatically shift.
I have purchased the kits for the valve control body rebuild, so I installed those. The bore for the 1-2 transition would compress and stick open. As I disassembled and reassembled, I made sure everything was good and felt smooth. After reassembling, the Ranger is in the same place. It will engage in all of the gears, reverse, and drive, but will not shift from first into second automatically as accelerating. It will shift into second manually on the column though.
I've heard it could be a vacuum issue, which makes sense with the changes made to seal off leaks seeming to be the cause the of issues. The fluid level drops when the truck is running, but I have not measured what the vacuum level is, nor how to measure it.
I have also heard a sticking governor can cause the A4LD not to shift from first to second, but am not sure what symptoms would point to the governor over anything else.
I love the truck and would love to drive it, but I'm not a mechanic so the diagnosis part is not my area of expertise. I always appreciate sound advice though. Thanks!