I have this annoying rattling sound in my Blazer, it goes away under acceleration, but at idle it drives me nuts. It is louder than my stereo unless I have it cranked. It was like this when I bought it and figured it was something I could take care of, and used it to help lower the price during negotiations. As it turns out, it's my PCV valve rattleing away in the engine bay. I have never had such a problem. I have a new PCV installed, but the same issue. I know it's the PCV because if I take it out of the valve cover and slightly block the hose end to keep the idle even, the noise is gone from both the engine bay and cabin. Hook the PCV back up and it's back. Are all Blazer's like this? Does anyone else have anything like this or have any ideas to help silence this thing? The little plunger in the valve vibrates like crazy and I just can't believe how loud it is. It almost sounds like it's installed in the dashboard it's so loud in the cabin. Any help would be greatly appreciated.
Will

 

Is the engine stock? Is the hose hooked to the stock location? Sometimes a small tower with two connections or three may be present, any of those blocked or pinched?

Reason to ask this question. Vacuum governs the PCV valve. Either too much or too little is present. It is my believe and others may choose to disagree, that the pcv valve should hold itself in the non operated position while idling. This is very important to heavy duty v8 motors that need all the vacuum they can get just to idle right. Vacuum being used by the pcv sytem is also NOT available for the engine to run other things. There is also less need for serious scavenging of the engine at idle. So, to me it ought to not be working.

Now then, you have one that wants to work only a little bit?????? lazy? Just kidding. Normal questions to ask you at this point are: What is idle speed? If idle is high, then it may operate because it is receiving enough vacuum to do so.. Second normal one is: Is that the RIGHT pcv valve for your EXACT engine. Dont know this to be true, but lets assume a 2.8 uses one kind, then if you have that model installed in a 4.3, you might be in trouble and get what you have even with a new one. One may take more vacuum to operate that the other.

What would I do before looking for too much vacuum for some reason?? I'd get one for a 350 and stick it in there and try it.. If this one solves the noise, then it still may give you problems the other way. It may not operate early enough. It would become a guessing game at this point, come back and give us a little more to go on.

 

Can you install a vacuum gauge? Summit racing has them at $12.95 and up.

 

My understanding id the PCV plunger should be all the way up and sealed shut during idle, as that is when the vacuum would be greatest, and blow by the least. The valve is the right one for my stock 4.3, and it idles at 500rpm when warm. Engine has a slight tapping noise, but otherwise purrs at idle. no stumbling or anything. The truck runs great except for this stupid rattling noise. Now the wierd thing is, under accel it goes away, which is when the PCV plunger would be pushed down by the spring and allow blow by into the manifold. I have not checked the vacuum, so I'll head down to Sears or NAPA and pick up a guage. Good tool to have in any case. I've checked the hoses and nothing is pinched or broken. I might actually try another PCV valve and see what happens. Any other suggestions?
Will

 

Yeah my writing is over the top a little but I should have mentioned that I consider "normal" The idling mode. I consider not operating the same as not doing any good??

The simple plan for testing vacuum to the PCV> Pull it out from the valve cover. At idle you should feel vaccum by placing your thumb over the end of the valve. It shouldnt make noise once you place your thumb over it.

If it still makes noise, the intake port or hose is clogged.

Little or no vaccum felt there is an indication that the vaccuum HOSE or INLET at engine are blocked or clogged. In my opinion a leak could also exist. So basically if it were a carb, a bunch of carbon might have it clogged. Throttle body is much the same. Dont know what you have, but vacuum has to be there. A good, usable amount of vacuum.

Yours does shake when you move it right?? bet it does if new.

Again, if this were a carb, then inside the air cleaner there would be a small filter. A small amount of vacuum should be felt there also at idle. You'll have to modify your testing according to what you have. Might be good to remove the hose and test at it. If you feel a slight amount of vaccuum after a little time. like 20-40 seconds, then the whole system ought to be working fine.

Of course yours isnt. So somewhere there is a leak. clog. Bad hose. Something is interfeering with the proper operation of things.

I would carefully check the port to the intake. They can get clogged and not give enough vaccum. This may cause the exact problem you have. Take hose and spray cleaner through it. Make sure its completely open. Check intake for vacuum as it runs with hose disconnected and, if neccesary, clean the intake port. Often this can be done with a spray of sorts and a small gunbarrell like brush. Carb cleaner is what I have always used on carb manifolds. Just be aware that this may make the engine start rather reactionary. it is after all a flamable, ignitable substance and you are sending it INTO the intake manifold. BE CAREFULL.

 

im having the same noise u r having....so did u fix the problem yet....sounds like something rattling in the dash during idle...but when u driving u do not hear it....let me know how u fix it

 

I am also having this issue. I am going to try to get vaccum tester but will be checking the hoses my self soon. If i find a solution i will post up. Does anyone know if this could hurt the engine at all?

 

I checked the hose which connects to the pcv valve and it definately does have vaccum.Pcv valve is new since the tune up last month. Any one have any ideas?

 

I have seen this problem on many of the 2001-ish model year blazers, It's somewhat normal for it to make the noise, but the reason it is transmitting the noise to the passenger compartment is because the throttle cable is contacting the PCV hose. Get a zip-tie and secure the cable away from the PCV hose and it will solve the problem.

 

Thanks for the reply Ill give it a look and see if that helps. While I know the pcv valve opens and shuts Im not quite sure if its supposed to do it continuosly. Its a weird problem to say the least. I am going to replace the pcv valve tonight just to rule it out.