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Hello all, this is my first post so we'll see how she do. I just installed a re-manufactured 5.4L to our 99" F-150 got everything hooked up and the motor runs good. It might be idling a little high. but the real problem is that when got everything ready to back the truck out it wouldn't engage. we checked fluid before starting it was a little low so we add maybe a couple ounces I didn't think much of it but in the Haynes book it describes after changing oil, filter, and gasket to fill with 4 quarts of fluid and then run the motor at mid throttle and move shifter from park to 1st a couple of times.Tried that, it didn't work everyone I've talk to so far thinks it's something electrical unpluged but I can't find anything loose or unplugged I did find a vacume line broken that was an easy fix you could tell where it went . but still nothing, willa OBD-ll read trouble codes from trans or sould I say caused by trans? also checked fluid when running/ fluids good.
There is nothing electrical that will cause a non-engagement. There is also no vacuum connection to the trans.
If it has enough ATF to read on the dipstick there's enough to make it work.
After an engine change with no engagement I suspect that the torque converter may have moved towards the engine a bit and become disengaged from the transmission pump. If this is what happened you probably will need a new torque converter and pump.
You could put a pressure gauge in the line pressure port on the driver's side of the trans. It should be a 0-350PSI gauge, but if you don't go above idle speed 0-100PSI should work. If there's pressure your pump is working and the torque converter is seated. I think you'll find there is no pressure and the torque converter and pump are history.