i just bought an 98 expedition and when you put it in A4WD the light on the dash blinks now is it suppose to do that or does some need fixed.

 

something needs fixed

 

Go into some snow or mud and see if you have 4WD.

 

The 4 hi works but when its in auto it don't is it one of the vacuum switches under the hood maybe

 

Send me a PM with your email and i'll e some pages from my manual. I think you are on the right track.

SECTION 205-03: Front Drive Axle/Differential 1998 Expedition/Navigator Workshop Manual

IN-VEHICLE REPAIR

Vacuum Reservoir —Auxiliary
Removal
Remove the front fender splash shield (16103) ; refer to Section 414-01 .
Disconnect the vacuum harness from the auxiliary vacuum reservoir and the A/C vacuum reservoir.

Slide the vacuum reservoir assembly out of the battery tray.

Separate the A/C vacuum reservoir from the auxiliary vacuum reservoir.

Installation
Follow the removal procedure in reverse order.

 

If the 4H works then it is unlikely the vacuum system is at fault because it must be working to engage 4H.

If you have a flashing warning, no 4wd engagement in A4WD, I would be checking the speed sensors on the t-case. If one is bad it will not know when to operate the 4wd shift motor. That is probably the cause of the flashing light.

 

That may even be the situation with my 98 expedition, everything works but the A4WD which is no worry to me, I hate the option for you never actually have 4 wheel drive in this mode. I either want to be in 4x4 or 2 wd.

 

That sounds like it's time for the Brown wire mod.

 

I have always (8 years) had the same blinking A4WD issue with my 98' Expedition EB. This year I had a vacuum leak which prevented 4x4HI engagement. My first thought was the t/c motor so I replaced it. Obviously it did nothing until I repaired the vacuum leak. My 4x4 works again, but I still have the blinks in A4WD

My question is this: Are the wires I swapped into the new t/c motor the "speed sensors" you speek of? And if so, which set operates the A4WD? (View from the t/c motor) The 3 to the left, three to the right, or the single tan wire on the upper right? Also, are they easy to replace and if so how are they attached to the t/c?

Or is the A4WD speed sensor on the rear axle, and if so, where? Thanks guys.

 

Check or replace your speed sensor(s) as that might be where the problem lies.

 

I think he is trying to...he is asking where they are.

 

Thank you Moto Mel and Alwaysford...............I'm sorry I may not have been too clear. I do want to know "where on the truck" the speed sensors are located. Is the sensor the wires that come out of, or are they connected to, the t/c? Or are they on the rear axle as some have suggested?

Also, any idea on price and where to get them?

 

They are pretty much the same and I bought one for my wife's 'Sploder from Autozone for about $15.00

 

That's not too bad. My question remains, where are they located on the vehicle?

 

There's one at each of the front wheels and one at the top center of the rear differential.