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Discussion Starter · #1 ·
I have recently become an Isuzu owner when I purchased a '96 Trooper last month. So far I have been very happy with it, but have come across a problem with my 4wd.

Whenever I try to engage the 4wd nothing happens. I can shift the lever easily and continue to drive, but the front axle will not engage nor will the dash light come on. However when I start the Trooper the light comes on briefly so I know it works (the light at least).

I consider myself mechinically inclined and have worked on many of my previous cars, but have no experience with 4wd/isuzu. When I have searched this huge forum I haven't been able to see anything that relates directly. I have came across some topics mentioning a vacuum hose but I haven't had time to investigate this on my Trooper yet.

Any suggestion would be very appeciated. Thanks.
 

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:roll: Hello, I too have the same problem you said, only it's with my 1997 Rodeo. I took it to my machanic and they said it's something with the modulars underneth, what ever that means. To some it up, it's electrical and he suggested I take it to the dealer. I'm holding off doing that, cause it sounds expensive. It anyone has an idea, I love to hear it.
 

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The problem with your 4WD is the front axle vacuum switching valve. It's mounted to the front of your front axle housing and has 6 vacuum lines and 2 connectors on it. The price may vary from state to state but the part goes for around $167.00 (in MA). You shouldn't have any trouble replacing it yourself....just be careful with the vacuum lines.....they can be stubborn to remove. AND DON'T LOSE THE CLIPS FOR THE CONNECTORS!!!!!! (you need to slide them out to remove the connectors) Hope this helps!
 

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Discussion Starter · #5 ·
Well I have finally found time to look into my trooper problem, only to come up with more questions.... I was able to locate the SOTF mechanism on the front axle. It only has two vacuum lines and one harness going into it.

I removed the vacuum lines to test for and suction. Now since I have no lift the Trooper was in park and idling. I did notice suction from one hose in regular 2wd. When I shifted to 4wd HI/LOW the suction disappeared, and the other hose had no suction like before. I assume the vechile must be moving for the vacuum to work right, is that right??

Also I was going to remove the SOTF mechanism to inspect it and see if I could possibly test it somehow, but I began to think of the fluid. I know it will leak and I don't have any handy. So I looked at the manual, hoping it would say if it's anything special. I noticed it listed the capacity but not type. It did list front axle capacity and "SOTF capacity" as two different values ?? Are these different? The SOTF capacity was very small opposed to the front axle, .13 qts or something to the matter. I found the front axle plug to fill, but I can't figure out where I would fill somewhere else for the SOTF. Is there somewhere else to fill?? And is there any special fluid, or is it just an axle fluid?
 

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Discussion Starter · #6 ·
Well I was able to troubleshoot the problem and get the 4wd working. I figure I'll post my solution here so anyone else having it will be able to search for the answer.

On the '96 trooper, the Shift on the fly mechanism (SOTF) is located on the front axle closer to the driver side. There is a guard which is easily removed with two 14mm bolts. After removal you should notice "two" vacuum lines going into the SOTF mechanism come from a switch located right next to it, which is used to engage the vacuum of the mechanism. In this case the Two switches were blue and grey, blue for 2wd and grey for 4wd. SO there are a few scenerios which would be a problem and not allow the 4wd to engage.

First the SOTF mechanism which engaged axle is faulty. To test this just apply a vaccuum to both holes, after removing hoses of course. While the vehicle is idling and the vacuum is applied you should be able to notice the 4wd dash light go on an off. That is true if your dash light works, which you can tell each time you turn the key and see if it lights up. In my case this mechanism worked fine.

Second the vacuum pump/lines bad. Easily tested by removing the two lines going into the passenger side of the switches, They should always have suction. In my case they did. If not follow them back to the pump, and check the hoses and connections.

Third the switches themselves could be bad. To test this you must make sure they are getting to the electric needed to operate. This can be done by removing there harnesses and testing with a 12v tester. While idling check for voltage while in 2wd in both harnesses and then in 4wd. If you are getting voltage, reconnect harness and check suction going into the SOTF mechanism. In my case I was getting voltage but the suction was not coming from the 4wd switch. The switches are removed with two 10mm nuts and after removing all the hoses. There are a total of six hoses connected to the switches. Note the place of the hoses to make it work correctly when reconnected.

I went to the dealer and was able to get the part. Luckily the part number was still on the side of the switch when I removed it. The isuzu part number for this switch is, 8-97101858-1. It lists for $160, quite expensive for something that fits in the palm of your hand. But now my 4wd engages so I guess I can't complain.

I hope this is helpful for current/future cases. I'm sure it would have been for me. I also have pictures if anyones interested, just email me. Thanks to everyone in previous replies, the info was able to get problem started and solved.
 

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I'm glad you got it working, though the selenoid did cost a bit. I have a similar problem, but in my case I'm not getting any voltage to the dark selenoid in either 2 or 4wd. The blue selenoid is energized in 2wd and is fed by the FADC relay in the fuse box under the hood. Got any idea what has to happen to get the dark selenoid to pick? It seems pointless to go yanking vacume lines until I get the dark selenoid to pick when shifted in 4wd. I've done my testing with the key on and the engine not running.
Thanks, ......Chris
 

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Relsom said:
I'm glad you got it working, though the selenoid did cost a bit. I have a similar problem, but in my case I'm not getting any voltage to the dark selenoid in either 2 or 4wd. The blue selenoid is energized in 2wd and is fed by the FADC relay in the fuse box under the hood. Got any idea what has to happen to get the dark selenoid to pick? It seems pointless to go yanking vacume lines until I get the dark selenoid to pick when shifted in 4wd. I've done my testing with the key on and the engine not running.
Thanks, ......Chris
i have the exact same problem, the grey solenoid has no power going to it, any thoughts?

thanks
 

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Great work heiney.5!

Maybe you can add the pictures and a schematic.
 
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