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Crankcase Vacuum?? WHY? HOW? WHAT NOW?

 
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Tim
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PostPosted: Sun Feb 13, 2011 4:19 pm    Post subject:  Crankcase Vacuum?? WHY? HOW? WHAT NOW? Reply with quote

Checking my oil cap for a "milkshake sludge" I found it seemed a bit difficult to take off. When I pulled it off, I heard an unmistakable SUCK noise. I put my hand over it and it was 100% vacuum on it. I've read that a bad PCV would possibly cause this, so I replaced it and the o-ring with it. Same situation. I've also heard this is totally normal on most BMW's. This thing is no BMW. Wouldn't crankcase vacuum cause abnormal crank seal wear and even cause some gasket failures?? Should I go invest in a valve cover breather? I thought those were to let OUT air, not suck it IN?

I'll go stick my vac. gauge on it to see what kind of vac it's creating.

info:
3.8L top swapped with GEN V blower, XP Cam, 250,000 miles on eng/trans.


EDIT!!!!!!!!!!!
I don't know who here remembers my post of the odd engine noise. But THIS ENGINE VACUUM IS WHAT'S CREATING IT! It's air getting sucked into the front main seal!! I can watch my vac. gauge I had hooked up to my oil dipstick tube, it would slowly climb up to 7in. Hg. of vac, then I'd hear the "odd noise" and I could watch it slowly go back down! I'm so glad it's not a cam bearing like everyone thought it was!!!

But I still need it fixed! I don't like dirty air getting sucked into my crankcase!!! >Sad

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nightryder
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PostPosted: Sun Feb 13, 2011 5:30 pm    Post subject:   Reply with quote

.....what? Confused

It's supposed to create a vacuum, if it was creating pressure out of the oil fill cap then that would be a problem with the PCV (and could blow seals/gaskets...potentially).

7in/hg of vacuum (at warmed up idle) is really low...mine makes right around 14in/hg with the same cam.

You have a vacuum leak somewhere (not at the crank seal). Check all the vac lines, the one on the LIM is prone to leaking. Did you properly seal up the EVAP on the blower when you installed it? Good seal on the TB?

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Tim
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PostPosted: Sun Feb 13, 2011 7:05 pm    Post subject:   Reply with quote

There's a little confusion here..
My MANIFOLD pressure is around 15-20 at idle (via sunpro boost/vac gauge in car.)
The CRANK CASE pressure was around 5-7in/hg of vac. (via a spare sunpro vac. gauge.)

My manifold pressure is correct. However, as far as I'm concerned, there should be a positive pressure in the crankcase. (by means of blow by from the worn piston rings.) Which is why it's a POSITIVE crank case ventilation valve. When there's excess pressure in the crankcase from blow-by, it re-circulates the gasses into the intake manifold. And prevents the compressed gasses from finding an alternate escape route. (Main seals, oil dip sticks, etc.)

What's all the hooplah on the PCV system on the series 2/3 hybrid motors? Is there a port being misused on my GenV blower? It's sitting on a series 3 LIM, so I'd think all should line up and work properly..

Thank you for your response!!

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PostPosted: Sun Feb 13, 2011 7:29 pm    Post subject:   Reply with quote

I think you are sorta confused on the PCV system operation... either way, I ran across this thread

http://www.fiero.nl/cgi-bin/fi.....ead=114181

Quote:
i have a gen v blower swap and you either have to tap a line into the tb for the pcv to work or run a breather. i chose the breather, it was like new for $10. if its stock format i wouldnt change it


It also states, if you don't have an L67 TB, you need a breather...


I would also check to make sure the spring, o-ring, etc are all correct w/ the PCV.. and make sure it's an AC/Delco, not some cheap knock-ff

BBEngineer

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Tim
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PostPosted: Sun Feb 13, 2011 7:41 pm    Post subject:   Reply with quote

Quote:
If you replace the stock throttle body on a 3800 SC or N/A engine that does not have provisions to allow for breather flow, you will need to add an external breather. You should never seal off the breather system as it can allow the PCV valve to draw a vacuum in the crankcase which can suck in seals and gaskets. You should never block off the PCV and breather system (seal the crankcase) because extra pressure will build in the crankcase due to blow-by which will blow out gaskets.


I'm not sure if I drilled a hole in my adapter plate for the PCV. I'm 90% sure I did, but then I don't know for sure what everyone is talking about the "external tube" that needs to be run is...

Well, looks like I'm buying a breather either way. I always thought those were stupid, but I guess I'm stuck!!

As always, thanks for the information!
Much appreciated!

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Sailor77
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PostPosted: Tue Aug 02, 2011 11:55 pm    Post subject:   Reply with quote

What did you figure out? I have a L26 with the L36 throttle body and ZZP adapter plate.
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PostPosted: Mon Aug 08, 2011 7:10 pm    Post subject:   Reply with quote

I just came across what you're talking about I think. Today when I was leaving a buddies house I got in my car, and the Low Eng Oil Lvl light was on, i left car running; pulled out the dip stick; dry....okay? that's weird, I just changed my oil and filter 350miles ago. I put a quart in, and it's almost full. I pulled off the oil cap while the motor was running and there is a HUGE vacuum under the valve cover in the front. From what I'm reading this is supposed to be? It also changes the sucking noise my intake makes when I take the oil cap on and off while the motor is running. Anyways, I put a quart in and it's fine for now, not sure where the oil went but I am keeping oil in my trunk, and going to look for oil spots wherever I park.

Any ideas?
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PostPosted: Mon Aug 08, 2011 8:39 pm    Post subject:   Reply with quote

In any pcv system, there should be restricted vacuum applied to the crankcase (through the pcv valve), and a fresh air feed (normally supplied by a tube somewhere between the air filter and the throttle body so only filtered air goes into the crankcase).

In a boosted system, if the boost source is ahead of the throttle body (i.e. turbo, centrifugal blower), there should be a check valve so boost can't blow into the crankcase via the fresh air feed.
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PostPosted: Mon Aug 08, 2011 10:57 pm    Post subject:   Reply with quote

billy101 wrote:
I just came across what you're talking about I think. Today when I was leaving a buddies house I got in my car, and the Low Eng Oil Lvl light was on, i left car running; pulled out the dip stick; dry....okay? that's weird, I just changed my oil and filter 350miles ago. I put a quart in, and it's almost full. I pulled off the oil cap while the motor was running and there is a HUGE vacuum under the valve cover in the front. From what I'm reading this is supposed to be? It also changes the sucking noise my intake makes when I take the oil cap on and off while the motor is running. Anyways, I put a quart in and it's fine for now, not sure where the oil went but I am keeping oil in my trunk, and going to look for oil spots wherever I park.

Any ideas?



Ummm, you have too let the car set a while too check the oil. I won't read right after you've driven it.

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How much miles are on those seats? How much pounds of ass were applied to the seat during every trip? Lol

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PostPosted: Mon Aug 08, 2011 11:02 pm    Post subject:   Reply with quote

PushrodPower wrote:
billy101 wrote:
I just came across what you're talking about I think. Today when I was leaving a buddies house I got in my car, and the Low Eng Oil Lvl light was on, i left car running; pulled out the dip stick; dry....okay? that's weird, I just changed my oil and filter 350miles ago. I put a quart in, and it's almost full. I pulled off the oil cap while the motor was running and there is a HUGE vacuum under the valve cover in the front. From what I'm reading this is supposed to be? It also changes the sucking noise my intake makes when I take the oil cap on and off while the motor is running. Anyways, I put a quart in and it's fine for now, not sure where the oil went but I am keeping oil in my trunk, and going to look for oil spots wherever I park.

Any ideas?



Ummm, you have too let the car set a while too check the oil. I won't read right after you've driven it.


The car was sitting for 3 1/2 hours prior to starting it and seeing the low engine oil light, there was nothing on the dip stick. I'm trying to figure out why there is such a vacuum in the crank case? The car ran differently when I took the cap off.
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PostPosted: Sat Aug 20, 2011 1:42 am    Post subject:   Reply with quote

Would like to just update this. I was getting a huge vacuum in the crank case (when pulling off the oil filler cap). Turns out I was missing a o-ring on my PCV Valve. Replaced the PCV valve, orings and all using the PCV kit from autozone...and the crankcase vacuum is now gone and my oil consumption is now gone.
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