4wd issues... again.

[Leo78]

So, ive looked through so many threads on so many sites my eyes are bleeding and have some things narrowed down... but no REAL answer. Hopefully a Master Tech out there can offer some insight.

So my issue is a recurring one with the 4wd system not functioning correctly. i dislike this model's "auto" feature altogether but whatever.

2 years ago i tore down the vehicle to replace the notorious timing chain cassette, and replaced the trans which was blown (along with the dtr, and a TC speed sensor) and some other minor funstuff at the same time.

So back then, when i put it all back together. the 4wd was still acting funny. the "auto" as i recall was doing the same as it is now, which is engaging 4high when it should not be. however, i never had problems with 4low engaging despite that. anyway, because i didnt feel like fOrK'ing with it, and lack of money... i just unplugged the TC since i dont use 4wd much anyway.

Recently (within a month) i plugged the TC in to play on state land, and the system was engaging and disengaging as it is supposed to... no problems. probably for a couple weeks drove fine.

Then my wifes truck was in the shop (ironically for something similar) so she had to use my vehicle. i get a text saying my explorer has the 4wd and 4low lights flashing at her. so she brings it home, and the lights are no longer flashing, but i can tell it is defenetely in 4High.

So, skipping all the screwing around with it that i did after that, Heres the full description of what its doing/not doing now:

1. Turn on vehicle, selector set to "auto" (dont even have to start, just key forward to ACC) and 4High engages. No dash indicator lights up in doing so, and listening, you can hear the gem module clicking a bunch, and usually the clunk from the engagement. Sometimes it engages, disengages, then engages again.

2. i also had a few times where there was grinding and free spinning, but i did figure out this was on the couple occasions when i started the truck and quickly put it in gear (D or Reverse) to move... because when you start the vehicle the TC starts in a neutral state and then after a few gem clicks, clunks into what is obviously 4high, starting it up and throwing it into gear before it has engaged results in a miss until it either spins down, or i change gear (D, N, or R, depending)

3. While the 4wd light does come on when you switch from "auto" to 4high regardless of whether its physically in 4high.... the 4Low does not /will not engage at all. No dash light, nothing. Switching from 4 high to 4low turns the 4wd light off, but no effect otherwise.


With the TC unplugged, the problem goes away, which i assume should rule out most if not all direct TC problems including speed sensors, shift motor, electromagnet clutch, ect. Though most of those problems could still be the culprit behind the 4low not engaging. the 4wd/4low lights do the 6 flash bit... but im assuming they should, with the TC unplugged.

The fact that it is actively engaging/disengaging the on demand 4high, while in "auto" mode, leads me to belive that fuses and relays are probably not the issue here. (ive checked fuses, but not relays)

So my best guess is that the GEM is a total P.O.S.
I know some versions of this control trac system are slightly different, in what exactly was controlled by what module.... im not sure if mine is controlled entirely by the GEM, or if it ALSO has a shift control module on top of the shift control relay.

So im hoping one of you professionals has a solid way to un-confuse me on this, and possibly provide some insight on how to diagnose the GEM/TCCM or whatever other module might be the P.I.T.A. here... because though logic tells me the GEM seems likely... logic also tells me that if the GEM was bad, id probably have other stupid things going on like windows, lights, locks or other accessories not working as well....

1997 explorer XLT, SohC 4.0, automatic

 

[Leo78]

Solved.

so i decided to do the brown wire mod, and pulled the shift motor off to clean and inspect it while i was wiring a switch for the brown wire.

upon inspection while cleaning the shift motor, i noticed that one or more of the pins in the adapter (male) were pushed/or pulled halfway out.

Not sure how one would have wiggled loose in the first place, but Because i had pulled and re inserted the TC plug a few times to disable/enable the TC when the 4wd wasnt functioning properly, apparently one or more pins in the male adapter got pushed or pulled slightly out.

extensive testing... and everything is fine. except for the now very metallic riddled fluid in the TC that i have to change because it had a couple times where it grinded between gears because of this mess.

 

[peades]

I think I'm having the same issue as you and I have been asking mechanics if they can just disengage the T-Case for me so I will essentially just have a 2WD vehicle. Every single one has looked at me with a blank stare and told me it cannot be done.

Is it as easy as unplugging the wiring harness from the T-Case shift module? http://www.explorerforum.com/photopost/data/500/27133Tcase20B.jpg

Also, what did you mean by the brown wire method? I was looking at buying a new shift module altogether since it wasn't that expensive and swapping it out. I am afraid it is not the main issue though and I'd be wasting time/money. I wouldn't mind driving 2WD until I can get a better grasp on the problem.

If I can just unplug it then I'll do it today before driving it home from work.

 

[Leo78]

Yes, unplugging the TC will effectively put you in 2wd... PROVIDING that it isnt an actual mechanical issue in the TC itself or something like the shift motor keeping it "stuck" in 4h or low. Alternatively you can also pull certain relay's/fuses or unplug the SCM but personally i found it easier to just get under the driver door and unplug the damn thing.

just be sure you A. tie the plug up and away so that it doesnt get caught on something and ripped out, and B. tape it off or something to keep dirt and water from crudding up the plugs because you will want to plug it back in at some point.

As far as the brown wire mod, if you read around the forums theres info and tips on it... but in a nut shell... these Transfer cases are operated by both the shift motor (external) and an electromagnetic clutch inside the TC.

there is a brown wire that comes out of the transfer case and inserts into the wiring harness plug... pulling the wire out of the plug disables the electromagnetic clutch, and effectively disables 4wd.

Unlike disconnecting the plug itself, pulling the brown wire shouldnt (as far as im aware) cause any dash warning lights and such.

by installing a switch onto the brown wire, you can turn the TC on and off at will simply allows you to ignore and bypass the actual problem.

i did the mod because im broke, and its an old vehicle im not going to sink a bunch of money into for the sake of having 4wd.