Suddenly I hears hissing by left fender, found this hose laying in between the 2 black things.

 

Theres a reservoir inside the drivers fender right about where the abs unit is.

 

Thank you,
Guess I cant just stick my hand in there ?

 

Not too sure, someone else will chime in soon that has, I just plugged it. Haven't had a problem yet... been a few months if not a year...

 

You can probably see it if you look down there with a flashlight.

 

did that to drive tonight, burned half the gas as usual. Coincidence ?.

thanks, will try it

 

An inspection mirror helps to show where it goes. If the hose is in good shape, you can make sure it doesn't come off again by using a zip-tie as a mini-hose clamp. However, if the vacuum hoses are original, they can be deteriorating and be losing their elasticity. The later could be why the hose came off.

I made a thread on replacing the hoses on my 1999 that has a 4-button controlled transfer case. the Thread is in my signature below.

 

Thank you Christine,
so it goes to the reservoir. Whats the purpose of reservoir ?

 

The reservoir supplies vacuum when the engine is under load and the pressure in the intake manifold rises up to close to atmospheric pressure, i.e. when it has "less vacuum". That is the purpose of the one-way valve that is inside the Tee connector to which this hose is connected. It looks like your hoses, or at least a few of them have been replaced but that this hose came off indicates that it might have aged enough to loose its elasticity and either should be replaced or as I suggested additionally secured with a zip-tie as a hose clamp.

The vacuum is used in several places on our Blazers. First it is used to supply vacuum to the actuators that direct to where the air goes in our HVAC systems. Second it is used for controlling parts of the 4wd system. On 3-button transfer case models, it it used to engage the front axle and to direct the transfer-case to switch into 4wd mode. On the 4-button transfer case systems (the ones with the additional Auto 4wd) the vacuum for the 4wd system is only used for the front axle engagement with the transfer case controlled electronically.

 

Thank you again Christine