Auto engage 4x4

[splintrcel]

My expy has the automatic engaging 4x4 but i really have never noticed it kick on when i have been driving in the snow. Is there a light or something that turns on when it activates or any sign at all. I am just curious and my 4x4 does work.

 

[FordandPolaris]

As far as I know there is no light that illuminates specifically when power is sent to the front wheels in A4WD. My truck has on rare occasion switched from A4WD to the full time 4x4 as if I had selected the 4H setting. Only happens in deep snow though, and only for a small amount of time. If your truck is between 99-02 i believe they dont have the option for 2H, so I would guess there would not be a light that would announce A4WD at all like in mine. Trust me, I don't ever notice the 4x4 engaging while in A4WD, but when I switch it to 2H in the snow, immediately I could tell that it was doing what it was supposed to be doing haha.

 

[tsgrpr97]

In a4wd there is always some torque being sent to the front, when slippage at the rear is detected the duty cycle to the trans. case motor is increased, slowing the rear and putting more load on the front. If the duty cycle goes to 100% then I think the 4 high light will come on.

Its working all the time and should be undetectable for the most part.

At least that's how I understand it

 

[toms89]

tsgrpr97 description sounds pretty accurate.

Straight from my cd-rom service manual:

Transfer Case —Automatic Four-Wheel Drive (A4WD)
Features and Operation

The automatic four-wheel drive (A4WD) transfer case uses an electronic shift 4x4 system that allows the operator to choose between three different 4x4 modes. The operator can switch between A4WD and 4WD HIGH modes at any speed. However, to engage or disengage LOW Range, the GEM requires that the vehicle speed is less than 5 km/h (3 mph), the brake is applied, and the transmission is in NEUTRAL.

In A4WD, the generic electronic module (GEM) varies the torque split between front and rear drivelines by controlling the transfer case clutch. Under most conditions, the GEM activates the transfer case clutch at a minimum duty cycle (percentage of time the clutch is turned on) which allows for a slight speed difference between the front and rear driveshafts which normally occurs when negotiating a corner on dry pavement. When the rear wheels are overpowered, the GEM detects this slip condition, and the duty cycle to the transfer case clutch is increased until the speed difference between driveshafts is reduced. In this manner, the GEM can redirect engine torque to the front wheels when the rear wheels lose traction yet still allow operation in the A4WD mode on dry pavement.

When the ABS system is active, the GEM will default to a minimum duty cycle for the transfer case clutch.


I never really noticed any light while in A4wd. Unfortunately I can tell when mine engages and disengages in the snow, rain, etc... but it may be my driving style. Or possibly mine is not working as well as others.

If I am light on the throttle I never notice.... but then im not sure if it is "activating".

 

[splintrcel]

i am impressed by this. I thought it was an on off thing. I really like that concept of shifting the power around instead of waiting for the car to just slip on two wheels and then switch to four. I will have to keep an eye out to see if i can notice it in action. Thanks guys.

 

[tsgrpr97]

I like it too, the only downside for me is the lower mpg. I was thinking of doing the brown wire mod and replacing the front diff with an earlier unit that has the center disconnect. I would rip out the vacuum actuator and use one of those manual conversion kits. That way I could have 2wd if I wanted. But so far I haven't felt that ambitious.

 

[splintrcel]

Thats true. Buying an expedition for mpg though just doesnt happen. Its the nature of the beast. I got my mpg pretty high for an expy but still room to grow.

 

[toms89]

I like it too, the only downside for me is the lower mpg. I was thinking of doing the brown wire mod and replacing the front diff with an earlier unit that has the center disconnect. I would rip out the vacuum actuator and use one of those manual conversion kits. That way I could have 2wd if I wanted. But so far I haven't felt that ambitious.

I read somewhere that ford said it only made a difference of less than .5mpg overall. Damn if I can find the link though and obviously can't verify.

Hmmm.. even so .5mpg is a big diffence in an expy.

 

[splintrcel]

sad that .5 is a significant factor when our mpg is barely a double digit number

 

[tsgrpr97]

.5mpg... that's another thing to remember the next time I start thinking about that swap. Might not be worth it.

What's normal for the 5.4 with the 3.55 axle? I'm getting around 12.5 mpg on average. Down to around 11.8 when we tow. I thought it shoulda been a little better than this. My 472 caddy does better than that.