highway16

New user here, but I have been reading posts and articles related to a problem I have with my Trooper, (Some background info) the vehicle which I got for free from a relative due to a blown engine . I purchased a new engine from a Isuzu dealer in Ohio. I had a local mechanic shop do the change over work. Prior to this I did not know much about the vehicle.
Fast forward to driving for about a year and I have found the shift on the fly does not work (High Range 4X4) . The switch on the dash when pushed does nothing, on the dash looking at the TOD nothing changes, the rear wheels are illuminated only. When I push the 4x4 shift stick forward, it engages into low range 4x4 and on the TOD all the wheels light up with the exception of the center transfer case light. So after reading some posts I felt the issue was with the vac unit located on the front right side of the axle. I removed it and purchased a new one and found no difference when replaced. I then checked the vac lines for suction, in which the 2wd line *(blue) had suction, then the *(gray) line with the high range switch pushed in it had suction into the actuator on the axle. I pulled the dash apart and checked to see if the TOD (high range switch was plugged in and it was. I am now lost in the trooper mechanical abyss . Looking for any one that has had a simular problem and how to get it resolved . Thanks for any help in advance.

WesBellmore

I JUST fixed my 2001 Trooper with this same issue... my does not have TOD, but it has SOTF 4x4.

Here is what I did:

Remove the skid plate that covers the two VSV (vacuum switch valves) mounted on the front axle. One VSV is blue, the other is gray.

Label and unplug all the vacuum hoses (3 from each VSV) and the electrical connector from each VSV. (The electrical connector is tricky...you have to pry up gently on a very thin brass colored spring clip on each side of the connector to slide the connector off.)

Used a NON-GREASY aerosol electrical contact cleaner and shoot it into each 'nozzle' of each VSV, then use a 12V battery to operate the solenoid in the VSV a few dozen times...this will free up the VSV if it is sticky.

When the VSV solenoid is working fine and air is going thru the nozzles when you blow into them, remount them, hook everything back up and you should be good to go.

Hope this helps!

fourwd1

I just had a similar problem on my 2000 Trooper w/TOD.
When I put in in 4HI or 4LO, the TOD display would just flash. CHECK did not come on at all.

I found the front axle wasn't locking.
After further troublehooting I found that the Connect (Lock) vacuum switch (the grey one?) didn't hold vacuum.
Unfortunately, parts stores don't carry anything remotely close (I did find a 2-port switch, but no 3-port ones). So $241 from the stealer for the 2 switch assy

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