92 blazer 4X4 problems

92 blazer electronic 4X4 4.3 vortec, Vin:W. light flashes a couple of times when trying to engage in 4 high, I can here the motor on the transfer case when pushing the button, pulled battery n checked diafram under the battery for the front differential, good holds vacium, put a vacium guage on the line to the diafram and started it up, every time i hit the 4 high button the vacium jumps to about 17 for only a secound, then back to zero, is it suppose to maintain steady vacium to the front differential diafram?? could it be the vacium actuator on the transfer case? their is also a tee off on the vacium line for the diafram just in front of the battery, larger hose and it dead ends on the fender in front of thr battery with a sensor of some type with a 2 wire hook up don't have any idea what this is for??

92 blazer electronic 4X4 4.3 vortec, Vin:W. light flashes a couple of times when trying to engage in 4 high, I can here the motor on the transfer case when pushing the button, pulled battery n checked diafram under the battery for the front differential, good holds vacium, put a vacium guage on the line to the diafram and started it up, every time i hit the 4 high button the vacium jumps to about 17 for only a secound, then back to zero, is it suppose to maintain steady vacium to the front differential diafram?? could it be the vacium actuator on the transfer case? their is also a tee off on the vacium line for the diafram just in front of the battery, larger hose and it dead ends on the fender in front of thr battery with a sensor of some type with a 2 wire hook up don't have any idea what this is for??

Have you searched the forums yet for solutions?

Check all hoses for cracking.

This is a vacuum loss or the electronic encoder motor is shot.

ok i just replaced the vacium acuator on the transfer case, now i'm only getting short bursts if about 5lbs of vacium to the front diafram under the battery, instead of short bursts of 17lbs to the diafram when i hit the 4hi button, and i checked all of the vacuim lines for leaks, also i noticed i hit the 4hi button and checked the front driveshaft ant it wouldn't turn,(while having the vacuim line disconnected and pluged for the front diff.) so the transfer case did engage that time but i can't seem to get it to do in agian

Have you checked the vacuum supply to the actuator switch? You found that you are not getting good vacuum to the diaphragm. Start back tracking until you find a good vacuum. Did you get the plug on the switch correctly?

Checking the vacuum at the front actuator is good troubleshooting just keep following it until you find good vacuum.

OK found the vacium leak, it was the boot in witch the 3 vacium lines conected to the switch on the transfer case. the plastic vacium adapters were pushed in to far on the boot so the boot would not go onto the switch all the way.

the motor on the transfer case at least sounds good, i can hear it run, now for the encoder can you buy this seperatly if so how mutch do they run (about) the encoder is plastic and has the 3 little nuts,(torque bit) attaching to the side of the transfer case and comes off with the motor assembly with the electrical connection on it?????