Hello, My name is Mike & I read about other people issue's with 4wd problem of the S10 blazer & was very helpful!!!!!! Followed the advise & found the vacuum line in the engine compartment disconnected.. Re connected & 4wd light came on, So went & tested & it worked!!! But problem I need help with is light went off when driving so I stop & re=engage $wd came back on stay on what could of caused this?

 

The first thing I would do is check for vacuum leaks. If you're losing vacuum that could cause the front axle to unlock.

 

Thanks for the reply, I found no vacuum leaks but what I need to know is I got the 4wd working by bypassing the vacuum at intake & plugging in vacuum line from the side of battery where the hose has a plastic black cap from 4wd line any suggestions? I unplugged it & put it back the way it was & no 4wd? Am I missing something?

 

So... Are you getting vacuum to the front axle actuator when in 4wd? If not, then you have a vacuum problem, period. The problem could be mis-routed lines, a failed switch in the transfer case, or a failed actuator.

If you are getting vacuum to the actuator while sitting in park, engine at idle, then you should hook a vacuum gauge up to that line and see what happens when you tweak the throttle. The vacuum should not drop by much when the throttle is tweaked because that vacuum line should be hooked to the reservoir (vacuum ball) side of the check valve. The routing goes from the intake manifold to the check valve / 'T' assembly, to another 'T', then the three branches go off to the firewall for the HVAC, to the transfer case vacuum switch, and to the vacuum ball. If that is all correct and you still experience drops in vacuum pressure at the actuator, then you must have a leak in the vac system somewhere.

 

I'll try that, Everything is routed correct to ball tees & actuator, The line I tried to intake was vent line & 4wd work, Is this bypassing actuator this way? I will try vacuum test at actuator but seems like maybe that is where problem lies.... I will repost with results... Thanks for all your help

 

No, it wouldn't be bypassing the actuator, but possibly could be bypassing or, more correctly, back feeding through a malfunctioning vacuum switch on the transfer case. It is also possible that the lines are not connected at the switch properly. The image below shows how the lines should be connected to the fitting on the switch:



The post linked to below has some pretty good explanations, much of which applies to all NV231/NV233 transfer cases when it comes to the 4wd actuation:Looking for vacuum hose diagrams

Have you inspected the check valve & made sure that it is both installed correctly & functioning properly? The check valve needs to be installed in such a way that it will not allow vacuum to escape from the reservoir, 4wd, & HVAC side of the valve, even when the line between the engine & valve is disconnected. You should be able to disconnect the line from the engine then disconnect a line from the other side of the check valve and hear the air rush into the system after disconnecting the line from the other side of the valve.

 

Ok I'll check switch thanks for the pics I know excatly where it at, I looked under car & seen it tough spot to get into but I'll check connections

 

I added/changed some things while you were posting. Check out the thread I linked to. It will help explain things a bit better than just the pictures alone would.

 

Ok, Update, All lines are running & connected as they should be to factory, Found no vacuum leaks & check for vacuum at switch on transfer case, Vac supply line getting vacuum to femalke connector on switch but still no 4wd, Tried reconnecting Vent line to manifold & fwd working with no problems, So I take it that my switch is bad at transfer case? It is plug in correctly at switch to make sure it wasn't crossed, So thinking I should buy at switch & start there first right?

 

Remove the battery and battery box. Under there is the vacuum servo for the front differential. The servo pulls a cable when vacuum is applied and locks the front differential in so that the front wheels drive. Think of it as an automated locking hub.

I have had two Blazers (92 and 95) that had bad servo's. The rubber gets old, possibly gets battery acid on it and then the servo leaks and will not pull the front differential in. When you get to the servo, disconnect the vacuum line, and use a hand held vacuum pump connected to the servo. Watch to see if the cable is pulled in. If not the servo is probably bad.

On my snow plow Blazer (92 used off road only), I chose to clamp the cable at the servo with a "c" clamp. The front differential is always engaged on that vehicle. If you choose to do this, make sure you block the vacuum line from the 3 port switch on the top of the transfer case. I did this workaround to save $100 on a new servo.

Bill