My wife’s 1991 Ford explorer is approaching 21 years old, and has been a most trouble free car.
A recent conversation about early snow, maybe even down low caused my wife to mention that button on the dash that says 4WD doesn’t work.
It hasn’t worked for a long while, and since the computer manages it, I hesitated to look into it earlier, funner stuff to do in the shop 🙂
One thing you need learn is to spend the majority of your time learning how something works BEFORE you attempt to fix it. This vehicle is NEVER in 4WD, so the parts that activate the 4WDH and 4WDL and back to 2H are not likely worn out..
Using google I entered “91 Ford explorer 4WD doesn’t work”.. I followed the links and quickly found a forum discussion and learned that Ford used this same system in light Ford Pickups as well.
I read thru a number of posts and found out the Service Manual was $80. I gleaned what I could from the posts and picked a most probable cause. What I learned from the posts is this system has what old computer geeks might call a code wheel, others would call it a position sensor, but whatever the case, part of the periphery has to be convinced it knows which of the three positions the transfer case is in.. 2H, 4WH, 4WL. Unless the system has a valid position, it will totally ignore your request. My symptoms, reported fixs all suggest a dirty or broken position sensor, or a bad wire or dirty connector to the sensor.
In a newer system, we could generate an error code, and store it to be read. If we were to look up such an error, it might say.. 4WD requested, current position unknown! but hey, this was the 90s, not so advanced yet 🙂
Here’s a picture of the rear of the transfer case, put a floor jack on the frame rail, driver side, and jack both tires off the ground.. add some jack stands for safety to get under here to look around. There’s a round harmonic balancer mounted back here with four bolts, 1/2 inch, remove same to improve the view.
Red Arrow on left is the Selector Motor, next arrow is the position sensor. There’s three security screws you need to remove, (harbor freight has the bits cheap if you don’t). make sure you make a mark on case, and case lid before you pull screws and cover so you know where to put it back.
I removed this cover and found wipers, and a wheel and traces. I used 600 grid paper to lightly wiped down the wheel and very lightly over the fingers,and then followed up with a lot of scrubbing down with new paper towel, then blew it down with air to get rid of any lint.
I slapped it all back together, and it works perfect. Why did I post this? Because I same as earned $500 or more this morning, I bet if I had taken it to the Dealer, it would have been more. The forum mentioned the New Ford motor sensor assembly is $525.00, I wouldn’t put it past my local dealer to sell me one. A penny saved, is a penny earned, and Isn’t that why we’re DIYs?