hey guys ive got a 4x4 issue right now. I got a 98 blazer 4 door ls 4x4.

I have the 3 button switch in the dash. im in 2hi, when I press 4hi or 4lo I hear a click in the kick panel where the computer is, and the light flashes about 5 or 6 times like its waiting on something to engage and then goes back to 2hi. It will do this the first 3 or 4 times I try it then it just makes the click noise in the computer.

I have relaced the 4x4 switch because the old ones clips where broken anyways, I took out the harness on back of the 4x4 computer and seen no corrosion in any of the pins, I cleaned it anyways and put some electric grease in it that didn't solve anything.

I took out the battery box the other day, had the engine running and had someone press the 4hi button, the vaccum diaphragm didn't engage or even try to move. I can pull the cable in on the diaphragm so I don't think the cable is seized up.

I replaced the transfer case switch today, the switch with a 3 prong vaccum harness on it, hoping that would fix it but nothing.

Im hoping one of you guys could lead me down the right path with some ideas so feel free to reply, thanks guys.

 

Ok there BB, so far good, need to see condition of the vac lines. The first place I would is the one that broke on mine. The line that goes right from the actuator to transfer case switch. Unplug that line put your finger or tongue on it, see if there's any vac.
Know you need same deal but in reverse, this time you need a line to the actuator, that you can blow on. If you here air coming out of it or its really easy blow you need one of those.

With all you have done it's gotto be some thing vac line related or the actuator.

 

You're right that the transfer case is waiting for something to happen, and like Jeff said, it's probably vacuum related. There is a switch on the right front axle tube that tells the TCCM when the right front axle is engaged. Can you hear the transfer case try to shift when you select 4WD? When the encoder motor shifts, it depresses the vacuum switch to supply vacuum to the actuator under the battery tray. Apparently the actuator is not receiving vacuum to lock the axle in and satisfy the switch. As a result, the transfer case shifts back to 2HI.

When the engine is at idle, unplug the vacuum switch on the transfer case. Does one of the three lines have vacuum?

 

no I don't here anything in the t case when I press the button, gonna check the vacuum lines tomorrow though ill let yall know.

 

If you're not hearing anything, like trying to shift, there's another problem... encoder motor, TCCM, wiring, etc. If the transfer case is not shifting, the vacuum switch will not be depressed, so it can't supply vacuum to the actuator.

 

ok guys today I got to lookin around. found that the vacuum line from my intake manifold to the vacuum tank (orb) up by the brake booster where it T's off was completely rotted, I replaced it, had good vacuum but still didn't work.

I checked the 3 prong vac harness at the t case switch and I had vacuum coming from the line going to the vaccum tank (orb).

so now im thinking either a bad vac line going to my vacuum actuator, or like captain hook said, my encoder motor or wiring.

Like I said all im getting when I press the 4hi or 4lo button is a click in the 4x4 computer in passenger kick panel.

Any tests you guys know of I can do to test my encoder motor or tccm or something?

Thanks guys.

 

Pull the TCCM out and take the connector off of it. Look for loose terminals in the harness connector. Check corrosion on the terminals in the harness connector and on the TCCM. Do the same thing at the encoder motor connector.

The transfer case is shifted by an electric motor, (encoder). If it doesn't shift, the vacuum switch won't operate. The case needs to shift before you can test the 4WD vacuum components, (vacuum switch, vacuum lines, axle actuator, differential locking mechanism, axle engagement switch, etc).

 

Thanks Hook, gonna try this tomorrow after work, ill let you know.

 

Sounds to me like it's the shift motor (encoder).
The TCCM is telling it to shift, but it's probably seized, so the TC stays in 2wd.

Rock Auto has them pretty cheap.
Here's a discount code for them and instructions on how to use it - RockAuto Discount Code - Expires 02/07/2014

 

I just took off the connector to the encoder motor and it looked good inside. I gave it a little brush and some electric grease still no signal.

I think ill probably just get an encoder motor sometime next weekend.
(Thanks for the link RJ2004)

Do you guys know any tests I can do with a test light or multimeter to make sure im getting the proper signal from my tccm to the encoder motor?