Hi there,

I've been trying to troubleshoot my 4WD not engaging the past couple days and I'm confused. I'll get to why, but first here are the symptoms. Switching to 4-Hi from 2WD, the light comes suggesting that it's working, but it obviously isn't. I found this out the hard way when I got stuck thinking I had 4WD engaged in a situation where I needed it, and the only reason why I got stuck was because it obviously wasn't engaged. Later on the drive home, I could hear a sort of rattling/grinding from the driver side, but only intermittently and only while 4WD was engaged. Driving home I was continuously switching back and forth between 2WD and 4WD hoping something would work itself out. Any, the sound only happened when 4WD was supposed to be on, and even then it wasn't a continuous noise, it only happened now and then.

Back home for a while now, some free time comes up to start having a look at what might be wrong. I am by no means a mechanic, but I am fairly good at following instructions and figuring things out, so using this forum and YouTube I start working things out.

First, it's not the transfer case. Front drive shaft can be easily turned by hand when the vehicle is in 2WD, and can't be turned by hand when in 4WD. According to the internet, that means transfer case is fine.

Where I got confused is when I started trying to figure out if the vacuum system is working correctly or not. I can't figure out if there's a problem there, or if it's the IWE (one or both). Here is the list of stuff I did to try to narrow it down, with symptoms/checks. Any help in determining if it's a vacuum problem somewhere, or one of the IWEs, or both of the IWEs, would be great.

Here we go.

1. With the truck OFF and sitting for several minutes, but with the 4WD switch on 4WD as I left it: manually turning one wheel causes the other to turn as well, but in the opposite direction.

2. With the key ON and the engine OFF: no change from #1.

3. With the key ON and the engine OFF but switch from 4WD to 2WD: manually turning driver side wheel causes CV to turn and the shaft to turn, but passenger side wheel doesn't turn with them. Manually turning the shaft causes BOTH wheels to turn. Manually turning the passenger side wheel causes the CV to turn and the shaft to turn, but driver side wheel does not turn.

4. Engine turned ON, switch on 2WD: manually turning the driver side wheel causes the CV to turn for both wheels, but the passenger side wheel itself does not turn. The shaft can be manually turned and neither of the wheels turn with it. Manually turning the passenger side wheel, it just freewheels (doesn't even turn its own CV).

5. Engine turned ON, switch to 4WD: manually turning driver side wheel causes the CV to turn for both wheels, but the passenger side wheel itself does not turn. Driveshaft doesn't turn with them and also cannot be manually turned. Manually turning the passenger side wheel, it just freewheels again (doesn't even turn its own CV)

6. Engine ON, unplug vacuum lines from solenoid on firewall behind battery: manually turning one wheel causes the other to turn at the same time but in the opposite direction.

7. Engine ON, plug vacuum distribution line directly into check valve from line coming from engine to supply constant vacuum with bypassing the solenoid: manually turning the driver side wheel causes trhe CVs to turn for both wheels, but the passenger side wheel doesn't turn. Manually turning the passenger side wheel, it just freewheels.

So, that's as far as I've gotten. Where I'm confused is that everything seems to make sense if the problem was the IWE for the driver side wheel, EXCEPT for the fact that the passenger side wheel freewheels even when the 4WD is supposed to be engaged. What's up with that? Either I'm missing something fundamental, or there's more than one thing wrong with this thing going on at the same time.

Please help! Thanks in advance.

 

The IWE locks with lack of vacuum, applying vacuum unlocks it. This thread explains how everything works:

https://www.f150online.com/forums/ar...then-some.html

 

I get that, but I guess what I'm looking for is confirmation that what I'm thinking matches my tests. So I guess I should be more specific.

So first off, I'm thinking that the driver side IWE is somehow seized in the LOCKED position, this would explain why the driver side wheel doesn't EVER free-wheel under any circumstances. If the IWE was NOT seized in the locked position, then the driver side wheel should free-wheel when there's vacuum applied to the IWE, correct? Well, vacuum should be being applied to the driver side IWE when either the switch is on 2WD (scenario 4 from my numbered list) or when I put the vacuum line directly on the distribution line (scenario 7). This should have unlocked the driver side IWE, right?

Now, on the passenger side, this is the one that confuses me. If this IWE was seized in the locked position it would behave the same as the driver side, but it doesn't. If the opposite was wrong with this wheel and the IWE was seized in the UNLOCKED position, then it should just always free-wheel. But it doesn't. It freewheels in scenario 4 when the 2WD is on, just like it should (and would if it was seized in the unlocked position). Also, in scenario 5 when I switch to 4WD, the passenger side wheel still free-wheels (again suggesting this IWE is stuck in the UNLOCKED position). BUT, then in scenario 6 when I unplug the vacuum lines from the solenoid, the passenger side wheel appears to lock (like it should if this IWE was functioning correctly). So the passenger side wheel is messing with my head because I don't understand how it can do what it does in 4, 5, and 6. Am I making sense at all?

 

I'd be checking both IWEs for cleanliness inside (pull them) and checking for vacuum at the IWE port with engine on in both 2wd & 4wd conditions to be sure both are getting good vacuum in 2wd and none in 4wd. Check hose ends at junctions too.