2004 4WD Wheel hubs not disengaging.. ever

[Al Steel]

Thanks a lot for the suggestions guys. Really appreciate them.

Update: Got a vacuum pump tester and checked both hubs. Thankfully they both disengaged when a vacuum was applied. Great so at least they work and don't need replaced. So I went ahead and got the solenoid because I'm and instant gratification kind of guy and I figured that since both sides were good that it was pretty logical that the valve was the most likely culprit. Plus it was a failure waiting to happen and got the TSB part with the hood. Installed it... no change. grrrrrr.....

Ok so I started checking the lines with the engine running and noticed a very slight audible hissssss when coming from the 3 way check valve downstream of the the solenoid. So I pulled the hose and noticed there was no vacuum on the solenoid side of the valve but there was on the other side. Ok, so I removed the valve and put in a T-connector and VOILA! both front wheels freed up. Awesome! Problem solved, bad 2 way check-valve, right? Not so fast, I tested the check valve and it seems to be working correctly. So now I'm really confused. I think the PO or another tech may have installed the valve backwards but I need a diagram that shows how the vacuum system works to know for sure. I don't think it's the check valve downstream of the solenoid because with the T in place everything works correctly.

One thing I do know is now I'm on the right track and with the hubs unlocked the Expy drives like a totally different vehicle. I'm no longer spinning 2 axles and a driveshaft so the vibration is gone and I'm hoping I'll recover a little more gas mileage. I just want to get the system operating the way it is supposed to.

Any further help is greatly appreciate. Thanks!

 

[Al Steel]

FIXED!

Good grief Charlie Brown! So after all that the fix came down to 2 things.

#1 - The audible hiss was a dry rotted manifold rubber "boot" that connects to one of the large vacuum lines for PCV. While this may have only been partially related to my issue, I think it was causing an intermittent CEL and low vacuum strength which COULD have cause partial disengagement of the hubs. Wrapped it with some duct tape until I can get the part replaced.

Here's a pic of the temp repair:




#2 - FINALLY, my issue with the 4WD locking hubs was... the 2-Way vacuum control valve was installed a$$ backwards! The way it was installed would never allow vacuum to the solenoid or reservoir. Hence the 4WD hubs always being engaged. Swapped it around and the 4WD hubs engage and disengage perfectly which is why my temporary fix of a "T" junction worked fine, sans check valve. My guess is that the PO had the car worked on (there are lots of new parts and evidence of repairs in the engine bay) and the tech pulled the valve only to reinstall it backwards.

I should have noticed that earlier, BUT in my defense, I couldn't find a diagram or a way to tell exactly where the IWE system drew its vacuum and from which direction. FYI, the LOWER port on the solenoid should always have vacuum when the engine is running. The UPPER port of the vacuum control solenoid has vacuum commanded on or off to engage or disengage the wheel hubs. It took a bit of tracing the vacuum lines to find that little nugget of information. So the lower connection port is the "supply" the upper is the "controlled" port. Turn off the engine or engage the 4WD and the solenoid shuts off vacuum to the hubs, locking them. Turn on the engine and set it to 2WD and the solenoid opens the port, pulling vacuum on the lines to the hubs and they unlock.

Here's a pic with the orientation corrected. My switch was installed the OPPOSITE way to the check valve was preventing any vacuum from being pulled on the IWE side.



It's worth noting that I bought the vehicle this way and part of the reason that I got such a good deal was that the PO thought it needed a $1200 front differential replacement because of the vibration and front end noise. He even took it to a local shop to diagnose it. I ALSO took it to a shop and they told me $980 for a used diff. WHICH, in hindsight would not have solved the problem! Instead it was a ZERO dollar fix. Actually it cost me $80; $50 for the replacement vacuum solenoid switch that I didn't need and $30 for the vacuum test kit.

SOO glad it wasn't the diff though.