The logic behind the BCM

[Ozwynn]

So? What is the logic or critical thinking behind the multiplexed wiring and the body control module in the F-150/Expedition?

mine is going out, or is gone. I disabled the awd part of my transfercase in my expedition so I have to switch it to 4wd for 4wd to work. it no longer happens automatically, or thats the theory anyways.

My Expedition randomly engages 4x4 (with the light coming on and everything) regardless of switch position. I shift to reverse and 4x4 disengages unless its in 4lo. I shift to reverse and my wipers quit until I shift out of reverse (I looked for a short in the column, there is not one). This morning my Driver side front window developed its own personality by randomly going up and down on its own, even with the key off (I pulled the relay. all the windows still work properly except the DS (how does that work? how is the dsf window on a seperate relay?)) to solve this problem as I was not driving 30 miles with my finger on the window button.

seriously wtf?!?!?

being a 99 ford no longer supports this body style. any from a junkyard is likely to have the same problem.


I don't recall any other Ford I have ever owned having these problems except an F-150.

76 F-100.......nope
79 F-250.......nope
91 ranger......nope
88 ranger......nope
91 explorer....nope
91 B2...........nope
89 B2...........nope
88 B2...........nope
91 Bronco.....nope
92 F-150......nope
95 F-250......nope
96 F-350......nope
97 F-150...... yes
99 Expedition. yes
00 Excursion..nope

all of these were wither XLT, Eddie Bauer, or Limited and one was a lariat. all had power windows and except for the 91 ranger and 96 F-350, all are 4wd.

can the bcm be bypassed (like wiring everything direct)? thereby solving the issue not just fixing the problem?

with the 4x4 randomly engaging I am getting 6 or 7 mpg. I am just going to drive my excursion. I can get 10mpg driving around SouthBend with it. I am tired of dumping money into the Expedition so I can have a Winter beater.

this winter, since jan 3:
Rusted brake lines ($183)
Failed air ride ($570 for strutmaster airride delete kit) (I actually fixed this in december)
Failed air ride labor ($225) I wasn't going to do that job in sub zero temps in the snow
rusted through trailing arms ($471)
rusted fuel lines ($230)

I'm just going to take it apart and fix everything as a longterm project.
I am using 2qt oil a week with no visible evidence of a leak. it does have snot in the oil fill (I hope thats from condensation) and I hve an unexplained coolant loss but no coolant in the oil at the last oil change and no snot on the dipstick. (I wonder if its going into the transmission)

 

[simpler=better]

Sounds like a ground/ voltage issue or a shot controller. What's the alternator putting out once you're spinning above say 3,000rpm?

 

[Ozwynn]

alternator is putting out. I show a steady 14v on my ispro voltage gauge. and the Deka Battery I bought in jul.

 

[adsm08]

Believe it or not the GEM started as a fuel economy thing.

By networking the car's electronics and assigning many formerly disparate functions to a single module the engineers were able to cut enough weight in wires and modules to be able to reduce the size of the brakes, making the car even lighter.

The Crown Vics (the only car that stayed the same enough for a good comparison) actually gained several MPG in the deal.


The driver's side window is a weird one, particularly if you have the one-touch down feature. Since the driver's window isn't locked out by the window lock, so it is on it's own system.

 

[Ozwynn]

we call it the Devil Truck.

 

[adsm08]

Did you ever look to see if your GEM had gotten water logged?

 

[Ozwynn]

tell you the truth, I don't know where its at.

 

[85_Ranger4x4]

Ford isn't totally stupid, if that part was a common fail point they would still make modules and happily sell you a new one.

For crying out loud they still make Duraspark modules and how long as it been since a new vehicle had one of them?

If you can't get a new one I would try a JY one or three.

 

[adsm08]

tell you the truth, I don't know where its at.

Under the dash, driver's side. The interior fuse block is part of the GEM. Take it out, crack the case open, and look inside.

Here, read this. Given your location and symptoms I believe it applies to your situation, which is why I am telling you to look for green corrosion. That is the tell-tale.

http://www.ford-trucks.com/tsb/fulltext/show_article.php?tsb=98-9-13

Next time I am around a JY I will look around for early Expeditions that could be GEM donors for yours.