1999 Expedition 5.4 AWD Eddie Bauer with air suspension removed approx. 180,000 miles

I’m having trouble with my 4 wheel drive system. This thing has given me trouble since I bought it.

Symptoms : Loud THUMP THUMP THUMP when placed into 4LOW.

Solution #1: Replace transfer case shift motor. Did not fix the Thump

Solution #2: Replace transfer case with a used one. Fixed the Thump but now has lost 4HIGH

Moved the new shift motor over to new transfer case at time of replacement. Rewired plug per instruction sheet. Replaced fluid with Valvoline full synthetic MERCON V.

Changed out selector switch as first one had bad light bulb. Switch OHMs out fine.

Have removed GEM to inspect for water damage. No indication of water entry.

Have also checked all fuses, all test good.

When operating the switch to go from A4WD to 4HIGH there is no relay clicks to be heardand neither the 4x4 or 4HIGH indicators light up in the dash. When moving the switch to 4LOW I can hear the relays clicking and get the THUMP as the transfer case changes gears.

Only thing I can figure is there is a bad sensor in the transfer case or the GEM has gone bad. Does anyone have the troubleshooting procedure for the sensors in the transfer case?

 

Don't be too quick to dismiss the possibility that the transfer case you installed is no good or not fully compatible.

Here are the pinpoint tests...all 95 pages of them...enjoy!

 

Thank you sir. Most of that looks to be a bit above my paygrade. I will need some time to go through all of that. Wish me luck.