Horrible screeching noise from engine: with the belt OFF. Is my engine toast?

The intake manifold can range from being under heavy vacuum when idling, to being pressurized under heavy throttle. The PCV valve opens under vacuum to suck gasses from the crankcase (where they build up pressure and can cause oil leaks around the pan if the PCV system is plugged up) where they can be further burned in combustion. Under throttle the valve closes, prohibiting the manifold's pressure from further pressurizing the crankcase (which can cause more oil leaks around the pan). Here's a useful detailed explanation of how the system works: http://auto.howstuffworks.com/positi...ion-system.htm

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Originally Posted by cheatah faheatah

Thank you for that prompt and extensive reply. However now I have a few follow up questions.

1.) How is your engine pulling vacuum on both sides ? If the "P" in PCV stands for positive, then if your pulling vacuum in the bottom end shouldn't it be negative crankcase ventilation? I thought pcv was there to let pressure out from, say, piston ring blow-by (compression chamber pressure escaping past the rings) Example: I had an 83 Bronco with rings so bad (from abuse, my bad, 20 year old me knew EVERYTHING, Ya right) that after a short trip on the highway, I would find the dipstick had "shot" up 8 inches or so...

2.) I know you didn't pinpoint the actual source of the noise, but what do think it was? Some thing like a gasket vibrating? Like a blade of grass between your thumbs, or a Kazoo reed?(How many times are you going to see "Kazoo" in this forum? LOL )

3.) Forgive my ignorance, but where is said pcv valve? I've never really noticed it. In other vehicles I've owned it was through the valve cover. You state it's under MAP sensor. Manifold Ambient Pressure, right? Please let me know where to look. (06 GP base)

4.) Why would the missing valve cause "blockage" ? If it's missing,wouldn't there be a free exchange of pressures/vacuums ?

Again, THANK YOU, and I look forward to conversing with you again..............E

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OK , bit of history. Cars USED to use a road draft tube that was cut at an angle and simply let excess gasses out into the atmosphere and supposedly the angle cut caused a light vacuum, but only would at like 100mph and and most cars wouldnt do that.

Positive crankcase ventilation means a device that positively remove crankcase vapors and pressure build up. By applying a vacuum to the crankcase you positively move those vapors and excess pressure AND it cleans up engine emissions.

The noise was the air sucking somewhere due to hard vacuum being applied. Now this can cause excess ring flutter, severe oil consumption and other runnability issues.
who cares about where noise came from, he fixed issue and unless it develops a leak of some sort, best leave it alone.

Others have answered the other salient parts asked.

7 month old thread now.
Problem has remained *solved* since installing a PCV valve. Car runs fine.

A little history on this 2001 Grand Prix GT (there's another thread somewhere with details): My wife and I bought this car in 2003 (for my wife; I owned a `97 Bonneville). We sold it to a neighbor in 2010. She gave it back to me (no cost) in 2016 with check engine light and codes for emissions and ABS brakes. Ultimately the Air Injection Reaction pump, relay, and check valve needed to be replaced, as well as the missing PCV, and the EGR got replaced a couple times, and I replaced the ABS controller with an identical one from a salvage yard, and that took care of all the emissions problems and the check engine light and codes. I did a TON of other work rebuilding the driver's seat, replacing the carpet, engine & transmission mounts, and a ton of other maintenance items to get it back into shape. It makes for a pretty good extra car for us, now with 209,000 miles on it.