I will add to this thread. I just swapped in a 2.9 where a carbed 2.8 resided. It wasn't easy, new fuel tank, sending unit with pump, had to mount the frame rail pump and run all new supply and return lines. Then there was the computer. Had to add all that in with all the wires for the fuel injection.
After I got done, I went to start it, it would not idle correctly. When it was cold and idling high it was fine, when it started warming up and the idle speed came down, it would start hunting. I could adjust the throttle screw and get it to idle smooth, but touch the throttle to rev it up and it would start hunting again. When you tried to move it around the yard, it truly was a Bronco, bucking and jerking.
After much experimentation I found out that the early 2.9's (this was a 1986 system) did not have a speed sensor. They had different idle strategies for idling stopped and running down the road, and this was determined by switches on the transmission and the clutch pedal. When I did all this wiring, I had left this idle switch loop open, ungrounded. It goes to pin 30 of the computer. I found out if I grounded this pin, everything settled down and I was able to drive it.
In fact it drives better I think than it ever did when it was in the truck with the switches supposedly working. Maybe they were not working that well, it was always a challenge to get going without stalling the engine. I permanently ground pin 30, and have been a couple of trips so far. I will have to see if leaving this grounded affects fuel mileage or driveability.
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