2001 Trooper Shift on the fly problem

Just bought a 2001 trooper with manual transmition. 77,000 mi. My problem is that when I press the 4wd button, the 4wd indicator on the dash flashes and the 4wd never engages. The transfer case seems to work fine. I have read previously posted info on what to check. I have checked the actuator as much as I could. I took it off and looked for corrosion. Didn't seem to be any. When I push the button, I hear the transfer case engage and the front drive shaft engages and turns as it should. The front hubs do not engage. Is there any additional items I could check to get the front hubs to lock in.
If someone can post info from a repair manual, that would be great also.

Are your tires all the same size? Same brand? Same mileage?

Yes, All are the same and I assume they are the same mileage. Appear to have the same amount of tread wear.

The easiest place to start based on your post is the vacuum system. It appears the front axle is actuated by a vacuum motor, so you would need to check that once the vehicle is placed in 4WD that vacuum is reaching the front actuator. If it is and seems consistent, then the actuator may have a bad diaphragm which you can check by applying a different vacuum source and listening for leaks or movement withing the axle. If it seems that vacuum shifts the actuator, then it could be an internal problem like the spline gears have worn or the shift fork is broken or some other problem. I suggest trying the above first. Good luck. ONe owners opinion. The electric switch is just for the indicator light to tell the transfer case control module when the axle is engaged or disengaged.


Time Chart of Shifting Under Normal Condition

Retrial
The motor actuator starts transfer gear shifting after signal from 4WD switch on instrument panel has been received. But the shifting may be impossible in cold weather or under high speed condition. When 2 seconds have passed since transfer gear shifting started and the transfer position switch dose not turn on (the gear (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/73323165/85779396/85779412/85779415/34853741/34860071/56233126/56234061) engagement is not completed), the motor reverses its rotation for 1.2 seconds and tries again to shift transfer gear. This procedure is repeated 3 times in maximum. While this procedure, 4WD indicator lamp blinks by 2 Hz.
If the transfer position switch does not turn on after aforementioned procedure has been repeated 3 times, the gear (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/73323165/85779396/85779412/85779415/34853741/34860071/56233126/56234061) shifting is stopped and 4WD indicator lamp's blinking changes from 2Hz to 4Hz to notify driver that the gear shifting is stopped. This blinking of indicator lamp continues until 4WD switch is returned from 4WD to 2WD.

2001 Isuzu Truck Trooper LTD 4WD V6-3.5L

Vehicle Level (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/73323165/85779396/85779412/85779415/34853741) http://library.alldatapro.com/images/a_003366.gif Transmission and Drivetrain (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/73323165/85779396/85779412/85779415/34853741/34860071) http://library.alldatapro.com/images/a_003366.gif Transfer Case (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/73323165/85779396/85779412/85779415/34853741/34860071/56233126) http://library.alldatapro.com/images/a_003366.gif Diagrams (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/73323165/85779396/85779412/85779415/34853741/34860071/56233126/56236114) http://library.alldatapro.com/images/arrow1.gif Vacuum and Vapor Hose Diagrams (http://library.alldatapro.com/alldata/LIB~C35748~R0~OD~N/0/73323165/85779396/85779412/85779415/34853741/34860071/56233126/56236114/14460237) http://library.alldatapro.com/images/arrow2.gifhttp://library.alldatapro.com/images/blnk_spc.gifVacuum and Vapor Hose Diagrams http://library.alldatapro.com/alldata/LIB~C35748~R0~OB0~P3R0H~N/0/73323165/85779396/85779412/85779415/34853741/34860071/56233126/56236114/14460237/86019510/85987369

Vacuum Piping Diagram

http://library.alldatapro.com/alldata/LIB~C35748~R0~OB0~P3R0H~N/0/73323165/85779396/85779412/85779415/34853741/34860071/56233126/56236114/14460237/86019510/86019511

VSV Assembly, Actuator Assembly

http://library.alldatapro.com/alldata/LIB~C35748~R0~OB0~P3R0H~N/0/73323165/85779396/85779412/85779415/34853741/34860071/56233126/56236114/14460237/86019510/86019512

That is some great info. Thank you very much. I am hopeing that actuator is the problem. Before I got this info from you, I had taken the actuator off and when I disconnected the hoses, I did hear air coming from the vacum line. Will be taking it to a mechanic that I know to have him look at it.
This latest info will prove to be valuable. Thanks again. I will let you know what happens.

Well, I got it fixed. The problem was the vsv assembly that engages the actuator. Replaced the part and it works like a champ. The hardest part was convincing the people that sold it to me that it was broke when I got it.
The Trooper is great and in great shape for the miles. Had a hard time finding a later model with an manual transmition. Thank you for you help.