Hey all,
I have a 95 4-dr. with 198K miles. Recently, 4wd stopped working. I had replaced the vacuum actuator (under the battery tray)a few years ago, so I thought that might be bad again. No such luck...it's good, lol. Keep looking. I found a vac hose, back near the t-case, that was broken & after a bit of searching, found the "3-hose" fitting that it goes to, & re-attached it. Now I have another "stray" vac hose that is baffling me. In the back of the intake manifold, a vac hose is attached, & heads towards the drivers-side. Directly behind the distributor cap, it a "T" fitting, with about 2 feet of hose attached...Where it it supposed to go?



Thanks in advance.

 

C"mon guys, Can you give me a hint?

 

On the driver side under the hood, near the back part of the wheelwell near the top, feel under the electrical boxes and see if you find a small protruding nipple. It will be small and barely noticeable. A mirror and light will help you look under the boxes. Some models have a vacuum ball inside the well and the end of the vacuum line would plug onto the nipple. I don't know if you have this feature. Now is a good time to replace the lines if they are degraded.

 

Thank you for the reply.
Mine does have the vacuum ball, and I have located the metal tube...It is already occupied. The hose that comes from the back of the intake DOES go to the drivers side, and splits off to several other things. My feeling is, this hose either goes "back", towards the t-case, or towards the passenger side.
The hose is about 2 feet long. It doesn't seem logical, that a hose that is already going to the drivers side, would "t" off, only 8" from the manifold & then head in the same direction.

 

My apologies, but I don't have a clue unless it goes to the HVAC system somewhere. We'll bump this back up and hope someone with a vehicle like yours will be kind enough to maybe look at their hose routing and reply. Good luck.

 

No apologies needed, Thanks for your help.

 

Yours is a 95 and I don't know if they used the same routing, but here's how the 97s vacuum is laid out;

Driver's side intake manifold port-
Hose to;
Driver's side outboard of the Brake Booster-check valve
3inch hose to
"T" - one port to the vac "ball" reservour, other port to;
"T" - one port goes in-side for the Heat/AC, other port heads to Transfer case;
"Front Axle engage Valve" mounted on top of Transfer Case. This is the "three port switch. It works like this "common port" connects to engage muffin unter battery tray, "Normally Connected" port goes to "Vent" which probably "T"s with Auto Tranny Vent then heads to a high point. "normally not-connected" port gets vacuum from the last "T" near the brake booster.

The "Vent" lines are black also and you cant tell by looking that they are vents. They cause a lot of guys to get confused. Their purpose is to keep water and dirt from entering the vacuum system, particularly if you drive thru deep water. When vacuum has the front axle "engaged" and you need to "disengage" it, the TC selector switch connects the muffin (which is holding a vacuum) over to the "vent" and it draws air in from the vent, thru the TC switch and into the muffin. If your "vents" are not properly connected, this process can get dirt into the TC switch causing it to fail after several times.

Here is a drawing;
http://dl.dropbox.com/u/837001/Blazer_Jimmy/Vehicle%20Vacuum.JPG

This drawing has two errors worth mentioning; There is no vacuum to the Cruise Control on most GMs, and the TC switch is drawn wrong. It show Vacuum applied to the Vent in 2Wheel mode. Clearly this is an error (I may edit this by the time you see it). But otherwise is a good drawing.

 

Hey Billbobagns,
Thank you so much for the great explanation & drawing. My system is very similar to the drawing & everything seems to be hooked up correctly. I have also replaced many of the original lines that were cracking, or loose from their fittings(one at a time,so no confusion). The only difference mine has, is an additional "t" fitting, about 8" from the "engine vacuum fitting. It also has 2 ft of hose attached. It's definitely vac, and not vent.
You mentioned... "Normally Connected" port goes to "Vent" which probably "T"s with Auto Tranny Vent then heads to a high point....
This may be the direction I need to look. Yesterday I noticed a "vent tube, or cap" tied to the Transmission dipstick tube. there is NO HOSE connected to it...well there WAS, but it has broken off. I can see (from underneath / pass side) the trans vent tube, but always assumed it was supposed to be "open". Maybe it is supposed to curve up to the front, to the dipstick tube & my "hose in question" might "t" into that. I'll look into that.

 

not sure if youve tried this already but check if all your HVAC functions are working correctly. in cases where the vacuum ball breaks or a connection is lost, both 4wd and HVAC will be inop. I believe the HVAC system defualts itself to hi-fan and defrost mode, so if you have no other modes, its in default. it this is the case, theres something missing in the vacuum ball vacuum circuit.

 

I just took a look at my 95 That Vac line runs from the Manifold over the top of the brake booster to a check valve that splits off to the ball, I attached a pic