Auto 4WD

[Kylewieder]

First Ford, first 4WD so I basically know nothing.
I do know while in auto 4WD my explorer shifts into 4WD possibly from strong acceleration while on dry pavement.
From what I've read this is normal but it stays in 4WD.
I got it out by taking it to some dirt and cycling the 4WD knob, shifting P-D-R back and forth in each setting.
So my question, is this normal to get out of 4WD or should it shift back into 2WD on its own?
Hopefully this hasn't been addressed already, I searched a lot of 'stuck in 4WD' threads already.

Thanks in advance

Update: It got stuck in 4WD again and the only thing I can think that triggered it was from strong acceleration again. I put it in 4HI rolled a couple feet put it back in auto which took it out of 4WD (no binding and whining on pavement)

 

[rb142]

Definitely not normal. Sounds like a problem in the transfer case. In auto, it should only engage the front when there is wheel slippage, and then go right back to 2wd. Sounds like the viscous coupling is getting stuck (or maybe a previous owner messed with the wiring).

 

[drdoom]

Also make sure you have a good set of matching tires. Check that carefully.

 

[SoNic67]

The way Auto 4WD works: takes measurements of rotational speeds of front and rear axle (two sensors in the transfer case). If those differ, than the 4WD Hi is engaged shortly, until the speeds match.
If your tires are different size or if one of the sensors is faulty, you will have a difference in readings that might trigger the 4WD.

 

[J_C]

I've noticed on mine that 4WD feels like it engages if I take off from a stop at medium acceleration rate making a hard, but not terribly hard turn, like at a stop sign at a right angle intersection. It doesn't bother me much at the extent it is happening but is this a sign of a problem that will get worse?

All tires are identical, inflation checked, and it doesn't seem to happen improperly any other time and drops out of 4WD right away once the wheels are straightened some, so it's engaging for maybe 2 or 3 seconds.

 

[Kylewieder]

Thanks for the replys. I'm hoping that it's the hall effect sensors since it's speed related and I can get it back out by turning the knob to 4HI and back to auto. I found a switch under the driver side dash that I'm hoping is a brown wire mod, I switched it, gunned the throttle and no 4wd. I'd like to make it right but the mod will do for the time being.

 

[rb142]

Your previous-owner brown wire mod may not have been done properly. That would be a good place to start checking for problems.

 

[Kylewieder]

I'll look into how the mod was done. I didn't think to check that, thanks.