problem with 4x4

My vehicle is a 99 jimmy with 4 button system.
Ok here is what happens, the truck starts out in 2hi I press the 4hi button, I hear a click from the computer on the right side, now the 4hi button
continues to blink, it will continue to blink never switching back to 2hi, now if I press the 4lo button the 4hi will stay on and the 4lo will come on, but when I put it in gear only the rear end is in 4lo, the back tires will spin in 4 lo but the front end has no power.
It is as if the valve in the front under the battery box isnt working or I have a vaccum leak. Any suggestions?
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If you join my forum I have info posted about that drive system complete with diagrams in member only area and some info in public areas too. ----------------- TheSnoMan.com
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wrote:

Check and recheck every bit of info you find there!! Most of the BS this idiots post's in friggin'wrong!
Roy
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If anyone posting BS its you Roy, I have the actual dealer manuals for that model and others (exact same one/system dealer uses) I can even look vehicals up by VIN here can you? ----------------- TheSnoMan.com
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wrote:

Hell, you can't even spell it. It is "vehicle" dick head. Now, why don't you go back to the V10 thread at aadt and correct your totally wrong answer. Then perhaps you can also answer the questions you were asked but chose to ignore. Oh, I suppose I'll have to adjust your sig here as well. It was a big hit at aadt.
Sorry if I've offended anyone here. It is just this pos posting BS info is dangerous

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I went there one time and I couldnt get the site to work right for me.

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Adam F wrote:

Yes, it's obvious that the front diff is not engaging. There is a switch in the front diff that closes when the fork that engages the front axle moves into the "engaged" position. If the t/case module does not see that signal, you will never get a shift into 4hi.
Depending on the year, you either have a number of vacuum lines running back to a switch that is on the drivers side of the t/case. One will be vacuum supply, one will be a vacuum line running to the vacuum motor sitting under the battery, and one is a vacuum vent line. The first thing to do is see if you have a good vacuum source to "that" switch on the t/case. If not, you need to fix that (obviously)....if you do, then you have to determine if the switch on the t/case is working...allowing vacuum to the front diff vacuum motor. Eventually, you should figure out where your problem is. Often, I'll start the other way round, apply some vacuum to the motor under the battery and see if the front diff engages....and work back from there.
The newer vehicles (and might include yours, can't remember) use an electric over vacuum switch which is mounted to the firewall right above the back of the intake manifold/distributor area. It was a problem, so if you have "that" system, take off the two vacuum lines, see if you have vacuum on one, if so, plug the two lines together, if you now have the front diff engaged, the switch is the problem.
Ian
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After putting the truck in drive and backing up about 10 feet it works! And since I did that its been working fine now, dont know why but everything is good now.
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