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Discussion Starter · #1 ·
I to am having the same issue. Heres what i know and what I have done. 1999 Amigo V6

Replaced VSV on firewall, getting power to both the blue and gray and strong vac.
Replaced diff sensor
Replace PCM under center console (computer)
Checked all vac lines
Check fluid in actuator.

When you push the 4WD button the front drive shaft engages, but not the front axle, if you reverse the vac's at the VSV the front axle does engage and 4WD works but light still blinks.
Same thing happens when i switch the vac's at the actuator.

it appears to me that the VSV is not cutting off and turning on when it should. The VSV is brand new.

So my question is what should i look at next?
 

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When the axle actuator is fully engaged the engagement switch sends an engaged signal to the 4WD control unit. Make sure the switch is working.
 

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Discussion Starter · #3 ·
do you happen to know the location of the switch? Again my vac's on the VSV do not change the va from blue to gray when engaged. So is there another switch on the transfer case? I do know i get no voltage to the DIFF Switch at the from end requardless if it is in 2 or 4WD.
 

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Discussion Starter · #5 ·
Are you refering to the vac in the front differential actuator? If so i have replaced that with a new one, the VSV's are brand new as well.

Again when you push the 4WD button it locks the front drive shaft but it does not switch the vacs on the firewall suction to engage the front axle.
When you manual reverse the vacs the 4WD works fine but the light blinks. With the vacs reversed it does take it out of 4WD when the button is pushed but the front drive shaft is still engaged and is a complete pig on gas.

So rather than getting out of the vehicle and reverse the vacs i really just want to repair the issue.
 

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It might be that little controller is burned out. Check and confirm power is going to it.
In off mode it pulls vacuum to keep it unlocked. Atleast you have means of getting it to engage if need be...
 

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Discussion Starter · #8 ·
No, the light still blinks when the lines are reversed when it is engaged or not when the lines are reversed.

I suspected the actuator switch should have some sort of volatage but i thought it was controlled by the computer under the console.
Does anyone know the location of the wiring of the switch? i treid to trace it but it goes into the wiring harness. All the fuses in the truck
are ok.
 

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The axle actuator switch grounds the wire going to the 4WD control unit when the switch is closed. One wire goes to ground the other to the 4WD control unit. If the 4WD control unit does not see the ground signal it does not know if the axle is engaged. On earlier models the switch is externally mounted next to the actuator, on some models it is inside the axle actuator. I suspect on a 99 Amigo it is inside the actuator.
 

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Discussion Starter · #10 ·
Ok, took out the acuator today and it seems to move ok when i applied air to both sides of the actuator. I tested the switch when it is hooked up to the actuaor and the switch does work.

So this leads me back to the VSV's not switching the vac when it is suposed to. I quess my next question would be am i supposed to get voltage to both the blue and gray at the same time?

Am i correct in thinking that voltage should only be appleid to one or the other, this to me would make sense that when the button gets pushed the 4WD should just simply change the VSV's vac to engage it.

I traced the wires and do not see anything out of the ordinary as far as shorts go. It there a relay or breaker somewhere that i am missing?
 

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The two VSVs are wired in parallel, one side goes to ground and the other side goes to the 4WD control unit. This suggests that one valve is normally open and the other is normally shut when the control voltage is Off. The one that is open provides vacuum to retract the actuator and the other side vents, when power is applied the reverse happens. I have a schematic, if I can figure out how to post it I will.
 

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Sounds good.

I'm also thinking these VGV's should switch when you call for 4wd. However my vcv's have power to them which puts vacuum on the 2wd side of the actuator when I pull the power plug on the vgv's they swap and put vacuum to the 4wd.

Like your problem I can't get the dam things to switch via the 4wd button on the dash.

Did you ever find the illusive "4wd control unit"?
 

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If yours is vacuum the sender screws in externally.
99 I think is the last year of the vacuum controllers.
My 2000 amigo had the electric servo shifter.
 

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My 2000 amigo's modual was up above the throttle pedal next to the heater box. I looked at my parts 99 amigo and didn't find it there so I'm at a loss for you guys. Unless someone knows where it should be or if that model has one .....???
 
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