'98 4wd in Auto mode constantly engages/disengages when accelerating

[JoelF]

I have a '98 XLT SOHC.

When in "Auto Mode" 4wd with the Control Trac system, it attempts to engage/disengage on dry pavement under acceleration. It makes all kinds of banging and grinding sounds due to the fact that that's it's engaging on dry pavement, which makes sense.

I've had it to the dealer twice for this problem already under warranty. One time they (supposedly) fixed a bad wiring connection and replaced the actuator, I'm assuming they're talking about the engagement motor.

Another time they said it was bad transfer case fluid and they changed it then told me that it needs changing every 15-20k miles because it wears out. Well, the problem is back and changing the fluid didn't fix it.

I would like to fix the damn thing myself but I don't have enough info on the transfer case system itself.

Has anyone had the same problem or similar symptoms? Is there a way to disable this setting and run as close to possible to 2wd only engaging 4wd when I need it by selecting 4H or 4L?

Thanks...Joel

 

[Robert]

First off, per the service manual that came with my '97 SOHC 4x4 Explorer, the change interval on the transfer case is every 30K miles under severe duty. The problem you describe sounds more like a faulty speed sensor that is intermitantly failing. It makes the GEM think your rear wheels are turning faster than your front wheels and engages the 4x4. I would start with the front speed sensor. Another possiblity is the wiring harness to both sensors. Make sure the connection is good. Your fluid shouldn't have anything to do with it but it is one of the more common suggestions made by Ford. Usually when a speed sensor fails though, it usually sets off your 4x4 and low lights. Do they come on when driving?

 

[JoelF]

Robert,
I haven't seen any type of lights or indication that anything has changed when this is happening. I did put the Control Trac into 4H momentarily to see if the symptoms were still evident. They weren't so I think you're on the right track because it does feel like the system is reacting to conditions such as wet or slippery pavement even though this is not the actual case.

If I remember correctly, the sensors used for the speed check of each wheel are the ABS sensors. I'll start with the front two sensors and also check the connections where they terminate at the transfer case.

In all honesty, I don't like the fact that I only have 3 modes of 4wd operation and no true 2wd setting. I would really prefer to keep it in 2wd but I know this system was not designed to do this.

Thanks for the information.

Joel

 

[Robert]

No, the speed sensors for the control trac are on the transfer case. The two front wheel sensors are used only for the front ABS, the rear sensor in your differential is for the rear ABS and possibly is used as the vehicle speed sensor (it is on the '99 and is not on the '97, I don't know about the '98). There are two sensors on your transfer case that measure the speed of your front and rear driveshafts. Since it appears that your Control Trac thinks your front is turning slower than your rear that is why I suspect that it is with the front sensor. If it is loosing connection or intermitanntly failing it would provide no output which would be interpreted as 0 MPH. If the rear sensor was failing it would think the rear was going slower than the front so it shouldn't try and transfer power to the front which it seems to be doing. You can disconnect the cable going to your transfer case shift motor to force it into 2WD. Your lights will flash, but see if you still feel the same problem. That is how Ford puts it in RWD when they run the Control Trac Explorers on the Dynos at their Allen Park Test Labs.

There should never be a reason to have a 2WD mode when everything is working properly. On my '97 it is pretty much transparant unless I am on a very slippery surface. In the rain, if I floor it I can feel the front "clunk" as it engages, but I really shouldn't be flooring it in the rain anyway On dry asphalt you shouldn't even know the control trac exists.

 

[JoelF]

To test your theory, I disconnected the four wires connecting both speed sensors and the problem went away. I actually like the way the truck drove after this. It was much smoother and quieter w/o the front drive shaft engaging. It also seemed alittle . quicker. This also tells me that one of the sensors is probably bad as you suggested.

I read some other threads related to this problem. One person by the name of MAV discussed the idea of removing the wires to the speed sensor to force the transfer case into 2wd. I'd like to replace the bad sensor to get the system working normally again but then add a switch to disconnect the sensors when I feel the "Auto" mode isn't necessary.

Do you think that this could cause any permanent damage to the transfer case and/or GEM control unit? I noticed that the lights did flash as mentioned earlier which I guess means a code is being sent to the on-board computer indicating that a connection or sensor is bad.

Thanks again for the advice.

 

[Robert]

That's correct. By disconnecting the sensors, the GEM isn't getting a signal back from them so it thinks something is wrong. Therefor, it disables the control trac and puts it into 2WD. The way that Ford disables the system is by disconnecting the wiring harness to the shift solenoid. Either way would probably work though. A double pole double throw switch to cut the signal from both sensor would probably result in the same thing. As long as you didn't mind the flashing lights, it shouldn't cause any harm. When you switched it back into regular mode, the lights should go off. you may want to try purchasing just one sensor. The rear one is easier to replace. The front one will require the removal of the transfer case shift solenoid. Maybe put the new on in place of the rear. If it doesn't fix it, put the one you took out of the rear into the front. You might loose a little fluid when you take the sensor out. I can't remember if they are above the fill line or not. If you do, be sure and put some back in through the fill hole until it runs out.

 

[espnfreak]

Robert, how much does this speed sensor cost? My 4x4 lights are blinking, but the system works fine. Can I clean this if possible? Also do i want to take it into ford since i have a xtended warrantee and 100 buck deductable? Thanks!

 

[Robert]

I've never had to buy one so I don't know for sure. I think they cost about $80 each, but again I'm not certain. I took mine out to clean them and found they were pretty clean anyway. You can try removing the rear one and seeing how it looks. That would only take a few minutes. I would be more concerned with the condition of the fluid if you find that your speed sensors need cleaning though. It should be replaced every 30K miles. (come to think of it mine is way past due )

 

[espnfreak]

Ya ok, i got amsoil and everything ready to put in the front and rear differentals. I will check the sensor when i get to doing this. I dont know much even about where the t-case is even located.

 

[Jim F]

Robert
Doesn't your 97 have a vacuum actuator for the front that the 98's don't have? By disconnecting the shift solenoid on the 98, will there be any undesirable wear on the front driveline?

 

[Robert]

The vacuum actuated front end went away after the '96 model year. Beginning in '97 it is all electro/mechanical. Beginning on the '97 model, the front axles are permanently connected through CV joints to the front differential. The driveshaft goes directly into the transfercase. There are cluthches inside the transfer case that are actuated depending on the signal from the computer. As the clutches are actuated, torque gets diverted to the front driveshaft. I haven't looked at a '96 and earlier but from what others have described, it sounds like there is a vacuum line running to the front differential (maybe to the hubs?) that fully disconnects the front wheels from the rest of the drivetrain. If your 4x4 choices are AUTO, Hi, & Low you do not have a vacuum actuated system. Only the systems with the choice of 2WD instead of AUTO have the vacuum system. Since yours is a '98 you would have the AUTO mode, hence no vacuum.

 

[410Fortune]

My mom's Mercedes had a similar situation. It kept engadging the "traction control" during acceleration etc... for no reason. Basically the sensors were telling it one wheel was traveling faster then the other even though the car was going straight. The problem was due to an under inflated tire.

Check your tire pressure and wear, I mean if your tires up front have less air then the sensor is gonna think they are spinning slower.....

Just a thought...other then that I would wire in my own switch (as discussed above) so I could manually force the system into 2wd, it will save you a ton of $$$$$$ in gas without that front driveaxle rotating allthe time.....

 

[Kinnish]

Hell...Just search for Jot017 and click on the disable AUTO in his sig...he put a switch on the Torque on Demand yellow wire on the GEM and it seems to work fine, minus the Flashing Lights, and it will give you 2WD Low...I have a 98XLT and I'm sick of the dang AUTO 4x4 and the loud noise it makes..especially with TT it is louder and abnoxious.

 

[Mascman]

Install the switch!!

I installed a switch on the yellow wire comeing from the GEM and I recommend it. The only drawback is that your lights will flash (6 times quickly-couple second pause-6 flashes, etc.) and to get your AWD back you turn the vehicle off, flip the switch on and then start the vehicle up. I only run in AWD when there is snow or heavy rains anyway.

Your axles will still be turning the frt driveshaft, but it will not be powered. If we could get some manual hubs then we could fix that, but I don't know of any. I thought there was a problem with my AWD untill I found out that it was supposed to add power during acceleration and then let off under normal throttle. I didn't care for it and like it MUCH better this way...plus it saves wear on the front tires.

Radio Shack sells a nice rocker switch that I put in the hole where the Cig Lighter was. (If you take out the lighter, be careful...the wire is live and you will need to cap it off.) It has a square shape that fills the hole up nicely and looks like a factory switch. I used a label maker at work to label 2 and 4WD.

Here is the thread...the picture is crummy but you get the idea...I have no regrets about doing this mod.
Dead Link Removed
Let me know if you have any questions I can help with.

 

[Robert]

If you want to know how much money in gas you will save before making the permanent modification, just disconnect the connector on your transfer case shift solenoid. That will put your system into a failsafe mode where it will be in 2WD only. Your 4x4 lights will flash though. Once you've seen how little affectit has on your MPG you may rethink making the permanent change.

The Auto 4x4 should have no affect on tire wear if everything is working correctly. My original Firestone Wilderness ATs had 1/4" of tread left when I got rid of them at 50K miles. My Michelin LTX ATs now have 40K miles on them and about 1/2" of tread left. I get twice the miles out of my Explorer tires than my Wife does on her Sable.

 

[Mascman]

Robert I wasn't implying that you are going to get twice as many miles from your tires if you install the switch.
As far as it being a permanent modification...just remove the switch and splice the wire back together...nothing too tough.
It is a matter of personal preference...I don't like it in AWD and that's that.
JoelF I would not go out and buy any sensors...unless you like to spend money for nothing! Install the $3.00 switch and it will drive like a normal 4WD should. That is my opinion.

 

[Adam Berger]

From what i've read on this thread, would I be safe in saying that my 1999 Ex doesn't even have automatic locking hubs?

 

[Robert]

Yes

 

[Mascman]

I did a test last night on my way to work. I live in PA and there are alot of hills. I put my AWD switch on and went to work. There is a long hill that you accelerate the whole way up and there is no run for it as you come around a sharp bend. First thing I noticed was a decrease in acceleration due to the power being distributed to the front wheels ( I normally disable the AWD). I flipped the switch to disable AWD and started to accelerate the way I normally do up that steep hill. This test and my own experiences with disabled AWD prove in my mind that you can't help but get more gas mileage.

If you live in the "Flatlands" and drive on the highway I agree that you will not notice any improvement in MPGs due to the fact that your AWD isn't actually doing anything at highway speeds on flat land.
However if you have hills and bends then you may like the way your Explorer drives with AWD disabled. With 33s and 4.56s and a 5 speed manual I am getting around 14 mpgs going up and down hills constantly.
Do a test for a week or so and then you can decide if it's a mod you want to do.

 

[Jon_Herr]

Guys, guys, guys...

There's a TSB to fix this problem.

They need to reprogram the GEM, or on older models replace the GEM but it's a known problem that Ford can fix.

I did it to my '98 SOHC AWD and life is great.

The tech described it to me like this:
The electromagnetic clutch in the transfer case is controlled by a pulse width modulated signal from the GEM. The area under the pulse is set to bring the clutch off of it's resting position and to the 'almost' engaged position. The fix involves reducing the pulse width so the clutch isn't so close to engaging.

When the clutch was held to the edge of engagement it would lock up on axle wrap and minor bumps.

If you need the exact TSB number I can find it for you, but the description of the TSB is something to the effect of AWD engages during parking lot maneuvers.