No 4th Gear in 93 Auto Trans

[Dora the X]

I recently purchased a 1993 Explorer. It is the first X I have owned. It seems to be in pretty good shape, but the tranny won't go into OD. I have spent quite a bit of time searching through this forum looking and learning.
I pulled codes using the jumper method. Here's what I got:
KOEO
111 pass
111
-----------1
157 Mass Air Flow signal is/was low or grounded
543 Fuel pump monitor circuit shows no power
157
543

KOER
111
111

Since I know the previous owner did some work on the X, but don't know all of what he did, and the check engine light is not on, I figured these could be old, resolved codes, and deleted them. I then took the X for a short drive, noting the TCC seemed to be working (based on the tapping-the-brake-while-cruising method) and again pulled codes:
KOEO
111
111
------------1
111
111

I tried entering the output state test, but didn't hear any solenoids buzzing/clicking. I just saw the check engine light come on/go off whenever I pressed the accelerator pedal.

I have located a wiring diagram online (AutoZone). From my reading on this forum, and looking at the diagram, I guess the next step is to check to see if:
1. I am getting power (+) at the 3-4 solenoid
2. The PCM is commanding (-) the 3-4 shift
3. If the signal from the PCM (-) is reaching the 3-4 solenoid.

Is this right? Am I on the right track? Anyone have anything to add?

Also, whenever I let off the accelerator while driving, the X seems to coast as if it were in neutral. I have tried downshifting to see if it would drag the engine, but it doesn't. Is this normal for these vehicles?

Thanks for your help.
Zack (Dora is the X)

 

[MrShorty]

That's how I'd proceed.

 

[Jack Flash]

probably some failure with the OD unit itself. OD band may be broken or not adjusted properly. OD clutches may be toast. or the OD servo may not be applying.

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J...all trans failures are not because of electronics...