I have 1999 blazer 4 wheel drive with 4.3 Vortec. Had a used 4.3 motor put in from 2000 Trail Blazer. Now I can hear a sucking noise coming from under the dash around the floor heater vents or thats where it sounds like. Didn't hear it before changed motors. Mechanic said there are no vacuum lines off. ???

 

Do all the controls on your heat/air settings work? Switching from dash vents to floor etc.?

 

Yes, everything is working fine as far as the heat and controls. It also idles bad as if it has a vacuum problem. I checked under the hood and all lines are hooked up. I don't know anything about under the vehicle or behind the firewall.

 

not to be an a$$, so you opened the hood and looked around not really knowing what your looking at or for? well the only thing under the dash that has vacuum are the vent controls.
try this: open the hood, on the driver side fender around the brake booster in the corner is a vacuum T. disconnect it and plug the hose that goes to the engine. once plugged go back inside and see if you still hear the vacuum his and if the engine runs any better. if it does the problem is after the T- and each section needs to be vacuum tested. give it a shot and let us know what happens.

 

Well then I would go to connected does not always mean good hoses. You need to check the hoses. I'm pretty certain you can check the hoses with starting fluid to find a leak. Wait for verification from another forum user before you do that, as I have not done this myself. Just to be on the safe side.

 

DON'T use starting fluid as it is very flameable and all it takes is a little spark and up in flames you go. Thats the first thing they teach you in school going thru for mechanics. but if you got theft and fire and dont care about the vehicle than go for it.

 

Saturday I replaced the pcv valve and while i was doing that i noticed 2 vacuum lines that were degraded. The pcv valve hose goes to some gadget and a vacuum hose runs from whatever that is to the T at the brake booster. I replaced that hose and the other 2 vacuum lines to that T one of which goes into the fender wall, which I just plugged b/c someone at advance auto said it would be ok. I'm planning on tracing that and see where it goes and fix it when time allows.

 

Okay, starting fluid is a no no.
The line going into the fender area is kinda hard to see what it plugs up to. There is a nipple there but you will need to use a light and a mirror to see it. You can feel it but seeing it makes it easier to get the hose on.