In 4WD (Hi or Low) or whenever the engine is off, there will be no vacuum to the IWEs. That lets the spring collar in each engage the hubs. The venting occurs between the IWE solenoid and the IWEs, not between the IWE solenoid and vacuum reservoir. Maybe I should have said the IWE solenoid releases the vacuum to IWEs; that might have been less confusing. The computer powers the solenoid, which then sends vacuum from the reservoir to the IWEs. When you shut the engine off, power is removed from the solenoid and the IWE side is vented to atmosphere so that the IWEs engage the hubs with the engine off. The only time there should be voltage across the IWE harness is in 2WD with the engine running. That voltage comes from the 4x4 computer module.

I got the "3MPH or less" for shifting into 4Low out of my owners manual.

 

Awesome write up. Best info on this site! This should be sticky'd in bold and a different bright color!

 

Actually I have to revise one part- I goofed in the placement of the check valve for the vacuum reservoir. I'll fix it when I get home. Vacuum has to pass from the reservoir to the IWE solenoid. What can I say, that was a lot of info to keep straight.

 

Sure is. My truck is at the dealer right now getting a new trans, and now new hubs and IWE's just got put on the list. May as well have them do it while I still have it under warranty.

 

I stickied this thread for now.... In a few weeks after you get some time to double check everything. I will move it to the how to section.

 

Sounds good. I'll get some pictures of the various parts and edit them in to help in identification.

 

Damn, how many km are on your truck? You driving the **** out of it or what? That's crazy. I still have the original everything and I'm hauling some serious weight regularly.

Special thanks to VTX1800N1 for all the info. The dealer took my truck in on Thursday due to some crazy s**t that happened. Left the truck in 2HI when I went for lunch, started it up and it was in 4LO even with the switch on 2HI. Couldn't get it out of 4HI, but the disengaged when it got to the dealership. Strange. Even more strange is that the dealer took stuff apart, tested everything vacuum and electronic and couldn't find anything wrong. Anyhow, thanks for the help. In the spring I'll have to replace both IWEs as they've been chewed up a bit by the faulty solenoid. Truck is driving just fine now.

 

Great thread! Wish I would've had it last year. However, I recently had my vacuum lines replaced. Not sure if new solenoid or not. 4WD light does not come on. but 4WD Hi works fine otherwise. Is there something simple that I could do (with limited back-yard mechanical capability), instead of bringing the vehicle in again.

 

Does the light come on briefly during the instrument self test when you start the engine?

If you still have the old solenoid (no rain hood) and it's shorted out, that will cause a no light condition but your 4WD will not work. Do the check of the transfer case I outlined above to make sure it is locking the front drive shaft in.

 

Here is another very excellent source of information on this system. Be sure to take a look at the .PDF files he has made available.

http://www.f150online.com/forums/art...replacing.html