i recently bought a 92 blazer (only had 70k miles on it, i couldn't resist) and now that it's in my hands and i've been able to give it a once over, i've notice something i've never before encountered.. a hissing noise coming from the steering column. it's constant, it sounds like air flowing, even when the truck isn't in motion and the wheel isn't being turned. if i turn off the engine it will persist for a few moments then slowly fade away.

i've been having trouble finding any information on such a problem and i'm frankly puzzled. it's maddening. anyone have any ideas? i was planning to tune the truck up and make it a daily driver but i'll admit i might have difficulty spending the amount of time i'd need to in it per day hearing what sounds like a radio tuned to a dead station.

 

most vehicles heater control switches are controlled by vacuum, might just be leaking behind the switch. i guess one way to test that theory is find the vacuum line going into the firewall and disconnect and plug it and see if you still hear it

 

interesting idea but it's definitely the steering column, not the heater switch area.. does it route through that area? does any other vacuum line go through that vicinity?

 

Does it have an air bag? I don't know when they first came out in blazers.

 

no air bag, not sure when they debuted myself either. the 92 is basically indistinguishable from a 91, the only differences are the all wheel ABS system and switching to the electronic 4wd shifter rather than the floor stick.

 

How about the brake booster? That's right near the steering column.

 

The first thing I would check is the vacuum line that goes from the cruise control servo through the firewall to the brake switch. That's directly below the steering column and attaches to the brake pedal. When the brake is not depressed the switch is closed. When the brake pedal is depressed the switch opens and the cruise control servo is vented to the outside air releasing the vacuum. If the switch is misaligned or malfunctioning it could be leaking vacuum right below the steering column.

 

an interesting suggestion toby, thanks. my load at work has had me working days too long to have any usable daylight, and today was the first day i've actually had since i got it off from work.. and naturally it stormed all day. afraid i don't have a garage.

i was only able to get an oil change done in this garbage and took the truck out for a little spin. i found while i was driving it that the hissing actually dissipates when i'm giving it gas, regardless of speed. 20 or 60, if i'm accelerating it seems to fade, if not outright disappear. when i take my foot off the accelerator, it resumes. does that oddity effect your suggestion?

 

What you describe is consistent with any vacuum leak. Engine vacuum increases under load. When you accelerate your engine is trying to suck in more air. That will change the sound that you hear from a vacuum leak.

 

if it increases under load, wouldn't the sound become more intense? sorry if my question is an obvious one, my knowledge of vehicle maintenance (like most newbies i imagine) is limited to those problems i've personally had to repair and heretofore i've been lucky enough to not have to pin down a vacuum leak.