99 XLT 4x4 electrical gremlin?

[Spunrod]

Hi all

I recently joined here after picking up a 99 auto sohc 4x4 XLT with 180k for my daughter. At $800 bucks it was a great deal for a cherry explorer with perfect leather and interior but it does have what appears to be an electrical problem with the 4x4. I've searched and read multiple threads but none have had the exact symptoms I have so I'm a bit stumped.

In auto mode it would bind and clunk under medium to hard acceleration. the "clunk" seemed to come from the front left wheel. I disconnected the wiring harness at the shift motor on the xfer case and the problem went away so it seems to be electrical in nature. When I reconnected the harness it was stuck in 4x4 low. Low light on and significant binding/wheel hop on dry pavement even though selector knob in "auto" position. Tried to shift out of low with tranny in park or nuteral and foot on brake with no success. Disconnecting battery for 15 minutes was no help either. Tapping the shift motor/transfer case lightly with a dead blow hammer had no effect. After several key off/key on cycles the 4x4 low light finally went off with the original problem returning, bind and clunk under acceleration. I drove it up on some ramps to play with it some more and the low light came on again when I stopped on the top of the ramps, selector was still in auto. Light turned off again after several key on/off cycles. Now I can't get it to shift into 4x4 low, 4x4 hi works fine but it just won't go into low using the selector switch. I should add that I hadn't tried to put it into low until all this started so I don't know if it ever worked properly from the get go.

I have searched for and read several posts that have similar problems but none were exactly the same. I don't know where to go from here as there are multiple things to check. I don't have a ton of money so I can't do the old "swap and see" and I really don't want to pay a dealership $350 to scan GEM/ABS for codes, at least not yet. Is there any prefered order to checking the electrical componets controlling 4x4 operation? Should I start with checking/cleaning the shift motor? Dash selector switch? GEM module? Shaft speed sensors or abs sensors? Relays? Is it possible I have multiple issues? It sounds like the BWM may take care of the clunking but I really would like to fix the root problem(s) so it works as designed to make it as user friendly to my daughter as possible.

Any suggestions or direction would be appreciated (such as how to check/clean shaft/wheel sensors). If it's not too cold or raining tomorrow I think I'll remove the motor and check it out as that is something simple I can do before looking at anything else.

 

[gijoecam]

Here's where I'd start...

Unless the clunking is severe, I wouldn't worry about it. Mine's done it since day-1. It's never gotten any better or worse, but it's always annoyed me. It's the primary reason I did the BWM. It does eliminate the clunking, although the system still tries to engage under hard acceleration. It's just doing what it's programmed to do.

Second, just to confirm, the vehicle should be stopped, in neutral, with your foot on the brakes to execute the shift to and from 4low. It's possible that, while fiddling with it, you got the magic combination by chance, and then weren't able to shift it back.

Now, if that's not the case, and you have an intermittent uncommanded shift, we need to work on pinning down that gremlin. When the low light comes on, is it actually in Low Range, or is it simply illuminating the light?

Lets start there... check it out and let us know.

Oh, and I would agree that even with teh gremlins, $800 is a steal!!

 

[Spunrod]

I didn't get around to checking the transfer case motor over the weekend, I watched football instead . I should be able to get to it this coming Saturday.

The clunking/binding is what I would consider severe and I would like to eliminate or at least reduce it.

When the 4x4 low light comes on spontaniously it is indeed in 4x4 low, it's not just the light. I can neither get it to go into 4x4 low or out of it by using the correct procedure, that is being in nuteral with brake depressed. It seems that the only way to get it out of low is to key cycle numerous times until it finally goes back to auto mode. There doesn't seem to be any pattern to it.

 

[toy720]

When you were checking the clunk and going ito 4wd were you on dry pavement as that will cause the binding and wheel hop (Especially in 4 lo) If this was the original problem.

 

[gijoecam]

If I'm understanding him correctly, the clunking sound/feel is under moderate to hard acceleration, at any speed, in any gear, on any road surface, and in 4auto. That's how I read his explanation.

In auto mode it would bind and clunk under medium to hard acceleration.

 

[Spunrod]

Just to claify and recap.........I am experiencing the "clunking" and binding on dry pavement in first thru fourth gear under medium to hard acceleration on dry pavement. It is most severe from a dead stop under hard acceleration. If I floor it from a dead stop or at low speed it will "clunk" and bind several times and diminish in severity as speed increases. With the wiring harness disconnected from the TC motor it does not exibit these symptoms. The clunking and binding sounds and feels pretty bad at lower speeds, I would not call it a nusance. When it occurs at speeds above say.....30 mph it is much less noticable and barely noticible when kicking down from OD to fourth on the freeway but it is still there. I'm leaning (hoping) towards the rear shaft speed sensor as that has resolved or improved these symptoms for other members, plus it's probably the cheapest fix.

The second issue which has now appeared is that it has spontaniously gone into 4x4 low own it's own a couple of times while the selector switch is in the auto position. It's done this while in park or while moving less than 3 mph in drive. I am not able to get it out of low unless I key cycle it multiple times and once it is back in auto I am not able to get it to engage low while in nuteral with the brake firmly depressed. I can engage 4x4 hi at any time.

I have no idea if the two problems are related or not. From what I understand the only electrical component the two problems seem to have in common would be the GEM. Unfortunately I don't have access to a scanner that can read the GEM codes. Rather than start throwing parts at it I will probably take it into a local shop that does have a enhanced scanner capable of reading all codes/modules and take it from there. I called around and there are suprisingly few other than the dealer that have the proper equipment. Anyone have a suggestion for a shop in the Redwood City, Ca area that knows Fords? Over the past couple of decades I have done almost all my own work and don't know of a good, reasonably priced, well equipped shop that people trust.

Thanks for taking the time to read these long posts. BTW.....this forum rocks! Lots of helpful people and good advise.