2001 B 3000 standard trans 4WD
I've had this loud whurrr whurrr noise for a month or longer, thinking it was vacuum because it would go away going up a hill in 4th and put my foot in in it the noise would stop. I checked all vacuum lines etc. no leaks. today I pulled the PCV valve out of the valve cover. the noise stopped . wow. ive got a lot of negative crank case pressure. if I put my thumb over the valve cover soon the noise starts again. so question what can cause negative crank case pressure? why is it sucking so much? its quite a bit, more than just regular vacuum. right now the only thing I can think of is lower intake manifold gasket leak? any ideas?

 

I think you should just replace the PCV valve. The engine is designed to have a negative pressure crankcase. The PCV valve is there to regulate that negative pressure. It sounds like you have a worn out or defective PCV valve.

The vacuum comes from the throttle body or intake manifold. A lower intake manifold leak would just lower the vacuum and decrease the negative pressure in the crankcase. Flooring the accelerator pedal also reduces the negative pressure in the crankcase lowering the amount of flow through the PCV valve, resulting in the noise stopping.

 

I have a new one to put in tomorrow that PCV valve it’s just amazing now how much negative pressure vacuum is coming out of the valve cover. I know that PCV valve gets its vacuum from the intake manifold. I kind of think these are two different things. We’ll see you tomorrow. Thanks for your reply

 

Should be positive pressure in the valve cover at the PCV port

When an engine is running there is "blow-by"
When a cylinder fires some of the explosion "blows by" the piston and rings and goes into the crank case, this creates a positive pressure in the crankcase and in the valve cover area because of the drain holes in the head and block.
As RPMs go up so does the Blow-by

In the old days there was just a vent in lower block or upper oil pan that vented this blow-by out
Because the blow by is HOT gases it will vaporize some of the oil on the piston sides and cylinder walls, this is the ONLY source of oil vapor in an engine, no place else gets even close to hot enough to vaporize oil

So in the old days these Vents would drip oil(condensed oil vapor) and spew out exhaust fumes, which is what Blow-by is

So the PCV system was added to end the pollution, untreated exhaust and oil vapor
The "positive" in positive crankcase ventilation(PVC) is not a reference to "pressure" but that the exhaust and oil vapor are now being dealt with

It has 3 parts, two hoses and a Valve
There is a Vent hose, also called a Breather hose, its usually on the air tube that comes from the air filter(so its filtered air) and goes to the opposite valve cover on a V engine of where the PCV Valve is located, on a 4cyl its at the opposite end of the single valve cover

Then a Hose connected to the intake manifold that goes to the PCV Valve that is in the valve cover
PCV Valve is a weighted valve so is pulled up/open more by higher vacuum, but its never fully closed

With new PCV valve installed pull out the oil dip stick
Start the engine
Use a piece of paper towel and hold it over dipstick tube, there should be a slight suction at the tube, that means the PCV valve/system is working as it should
If the paper gets pushed away then its not

Since all gasoline engines run using the same 18-21" of vacuum, PCV Valves are all pretty much the same for any size engine, just the case is different to fit the location and hose style

As an engine ages the blow-by increases, and with it the oil vapor, even new higher compression engines can have this extra oil vapor
A popular addition to a PCV system is a "Catch Can", its a "can" that helps cool/condense the oil vapor so it isn't sucked into the intake manifold

 

thats what I dont understand, PCV unplugged and removed the is a lot on negative crank case pressure at the valve cover hole. if I put my thumb over it and close it the noise comes back...im guessing its sucking outside air from a seal or ?? question what can cause this? this is quite a bit of pressure, more than the intake manifold makes.

 

Remove the Breather hose at either end and see if the negative pressure goes away
If so check your air filter and the hose/tube that goes from the air filter box to the rad support, the cold air intake

The breather hose uses Ported Vacuum, if the air filter and air box are clear, no obstructions, then Ported vacuum is very low at idle, close to 0
If there is a dirty filter or an obstruction then ported vacuum goes high so its sucking air OUT of the engine(valve covers/crank case) causing higher negative pressure

 

Thank YOU!!! im gettin the new PVC valve soon and then I'll check the other ports. I just did this, I removed the oil filler cap, with motor running I put my thumb over the hole on the valve cover, no noise. I put the cap back on and the noise was there. that vent tube must be closed. I tried blowing into it and its not very clear. I'll be cleaning it for sure.

 

ok I cleaned the tube from the cold air intake to the passenger side valve cover. Yes it was clogged and that was the problem all along. it was from when I had the heads off and there are buggs here that like to lay their eggs in little round holes. I blew out about 3 or 4in of those things. I totally understand the PVC system now. im still wondering where that negative air was sucking in from to make that noise. must have been a seal somewhere ? thank you all, and Ron pointing out what to check!!

 

Good work

Thanks for posting THE FIX, it WILL help someone else down the road

 

ok, im not finished like I thought I was, when I cleaned the air tube from the Cold intake to the valve cover I did take of the oil filler cap, I thought I put it in the cab. tube cleaned, all back to normal. but I can't find the filler cap. bought a new one. put it on and that closed the crankcase pressure. things have changed, there is still a lot of negative pressure . and today I found the old oil cap in the cup holder. I couldn't see it? so now I still have a small a mount of noise, and negative pressure like at PVC valve. also a misfire in cylinder 1 and a high idle? im thinking I screwed some thing up during this thing? or I should say the bugs got me me. but now I need to fix whats going on. the only thing I can think is the lower intake manifold gasket leaking? I'll pull the plug 1 tomorrow and see what it looks like? Ideas?

 

I think its time for a new thread ? this one is starting to get confusing.?

 

While engine is idling take the oil filler cap off
There should be NO CHANGE in idle
If there is a change then PCV system is not fixed

 

I pulled the oil filler cap, The idle does change but right now it’s at about 1500 RPM it won’t go down anymore when I pulled the cap it kind of went down and then came back up. There’s still a lot of negative crankcase pressure. If I pulled out the PCV valve they would still be negative pressure sucking in the valve cover. I can still even hear some of the noise, I believe there’s some kind of leak in the lower intake manifold? Also there’s a misfire in Cylinder one. I can feel it at idle but at a couple thousand RPM motors pretty darn smooth?

 

Also pull off the Breather hose

 

I'll try and explain this better, breather hose removed, oil fill cap on, PCV pulled out of valve cover. valve cover hole PCV side has neg pressure its sucking. PCV valve has vacuum line hooked up I can feel it. drivers side valve cover has neg pressure sucking twice as much. removed oil fill cap and breather hose and felt valve cover where the PCV goes, a slight amount of neg pressure. PCV valve in, breather hose off, I put my hand over the filler cap hole, lots of neg pressure sucking now where the breather hose goes. misfire cylinder 1 and high idle about 1500rpm. I think the AIC valve is working, I unplugged it and in a bit the motor died.

what can cause this neg crank case pressure ? right now I can just think there is a leak, lower intake manifold cyl 1 hole. creating the sucking and high idle? I know the PCV system isnt working, it can't. it needs positive crank case pressure . hope it makes sense ?

 

No, on what the "positive" means in positive crankcase pressure, it means the crankcase is no longer VENTING Blow-by(and oil vapor) to the outside air
"Positive" in this case means something was done to stop the pollution, Positive crankcase ventilation(PCV) system
Negative crankcase ventilation just sounds bad, lol, but its actually a better description of how the system operates

Only place in an engine that should have vacuum(negative pressure) is inside the intake manifold, this is created by the piston on its Intake Stroke, with throttle closed the cylinder tries to suck in more air than is available so you get negative pressure, called a vacuum, 18" of negative pressure at idle, and about 2" with throttle WIDE OPEN

The crankcase gets Blow-by, positive pressure, each time a cylinder fires some of that expanding pressure "blows by" the piston and rings and into the crank case, this is where all the oil vapor in an engine comes from, hot blow-by vaporizes some of the oil coating the cylinder walls and piston sides

The underside of the pistons going up and down does move the air in the crankcase but it just moves it around since the pistons up and down is balanced by 2 pairs up every 120deg in a V6, so as a piston comes down another piston is going up
So neutral for pressure

Not sure where your negative pressure in crankcase/valve covers is coming from with Breather and PCV valve disconnected
If #1 is not working there could be a hole in the piston, that would be a direct connection to intake manifold and the 18" of vacuum
If the intake manifold had a BIG crack in the bottom or under a runner, that would also be a direct connection from crankcase to vacuum

There is just not alot of places where the crankcase and vacuum run into each other on an engine

 

yes I know what youre saying, ive only had motors with blowby and yep I know when it comes from. the motor runs good above 1800/ 2000 rpm. its smooth and there's no smoke? I can feel the misfire when its idling. this all started after I replaced the heads. it ran good for a week, then the noise started. guessing the eggs in the breather hose blocked the hose. the loud noise started. I drove it a month or more. all gauges looked good and no CEL, after a while I got a CEL light bank 1 lean and something with the IAC. after I cleaned the breather I cleared the codes. now its misfire cylinder 1. im not ready to dig into it until I kinda know what im looking for, Thanks, this is a Mistry

 

this is where I think it could happen. its the only thing that I can think that could make the sucking in the crank case? make sense ?

 

Yes, intake manifold is the only place vacuum is created in a gasoline engine, so any place there is a nearby connection between intake and crankcase/valve covers could case the issue

 

Thanks, Im happy someone sees what im talking about. this started after I replaced the heads and the breather hose that goes the passenger side valve cover was clogged. that started something, back pressure or ? pressure. I'll order gaskets soon and pull the manifolds. fingers crossed this does it. if not, I wouldn't know what to look at.

 

ok just FYI I fired the motor the idle is high 1200 + after a few minutes it settled down and and all most died, I shot a few squiirts of starter fluid in the valve cover that has the hole for the hose that goes to the cold intake. RPM went right up. I waited a few more minutes the motor almost died again, a few more squirts again RPM took off. I think I found the problem.

 

Good test, yes, the intake is sucking in air from the crankcase/valve cover area

 

the other thing odd its using more oil than I would think. but it doest smoke? im thinking It must be sucking some ?

 

What started last October replacing the heads is now finished. Yes the lower intake gaskets were leaking. There was a piece missing in port 2, I might have come off when I removed the manifold? Port 1 I could see where I was leaking. But did it start when the breather tube was clogged and that created enough pressure to start the neg vacuum? Also the lower manifold bolts to me didnt seem too tight? that could have helped. Any way yesterday after buttoning it up, I did the flooded gas petal trick to get oil up to the heads. Varoom, the best its ever sounded and after a few minutes when it warmed up it even idled at about 800rpm, its never done that! Thanks to all that helped and gave me ideas and Ron who understood my issue and helped me finish this off. Time to close the thread Case Closed !!!

 

Good work

Thanks for posting THE FIX, it will help someone else down the road