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Old 11-12-2012, 04:03 PM   #1
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Default Excessive vacuum under valve cover.

Hey guys,

My 1.8L BP was recently rebuilt with new rods, rings, oil pump, bearings, etc. and I've noticed that there appears to be excessive vacuum build-up under the valve cover.

I've checked the PCV system, replaced PCV valve, made sure no vacuum hoses were plugged...

When I take the oil fill cap off with the car running and I cover it with my hand I can feel vacuum build up. Also, if I put the oil cap back on pull the PCV there is enough vacuum buildup that you can actually hear it suck the air in, almost like an air compressor sound. There MUST be a retarded amount of vacuum under the valve cover when driving...

Any ideas on what may be happening? I've gone through 3 new PCV valves just to be sure it wasn't that...

-Ryan
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Old 11-12-2012, 04:07 PM   #2
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One more thing before this happened I used to have the opposite port on the valve cover VTA and I noticed the filter I had attached was covered in oil. I assume this situation changed recently as there is so much vacuum under the valve cover now that I can't see any oil getting out... Maybe I should swap in a new valve cover? Possibility that the vacuum chambers are plugged? No idea...
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Old 11-12-2012, 04:54 PM   #3
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There is no vacuum while driving. Blow-by guarantees air is always being forced out -- this is why you saw oil buildup on the VTA port filter. As far as seeing vacuum at idle...is you PCV valve functioning/backwards? Seems like the only way you could see vacuum there is if the engine is pulling a lot of air via the tube from the intake manifold.
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Old 11-12-2012, 05:04 PM   #4
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Yeah PCV is connected as stock, which only accepts one orientation. At speed there must not be any vacuum there, but at idle it is what I would describe as extreme. If I pull the PCV valve out of the valve cover at idle after it has built up pressure over a period of 10 seconds it "pops" and you can hear it suck air in for a moment until it equalizes. Unless I'm just getting a bunch of **** PCV valves from Autozone...
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Old 11-12-2012, 06:07 PM   #5
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Are u confusing vacuum with pressure?
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Old 11-12-2012, 07:09 PM   #6
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Well, it could also be explained as negative pressure. When I remove the PCV valve and say, cover it with my finger, I can feel it pulling in. Same thing happens if I reconnect the PCV and remove the oil fill cap. The negative pressure or vacuum wants the cap to stay on. Seems jacked up to me and I can't find much online other than V configuration engines where there is a bad intake seal, etc. drawing air in... obviously we won't have that problem so I'm having a hard time figuring out what the deal is. If I had major blow-by wouldn't I have positive pressure trying to escape from the valve cover instead?
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Old 11-12-2012, 08:06 PM   #7
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It's not jacked up. It's normal.
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Old 11-13-2012, 03:56 AM   #8
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I'm still trying to imagine a scenario in which I would describe any amount of crankcase vacuum to be "excessive" short of the engine block literally imploding.
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Old 11-13-2012, 04:12 AM   #9
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Quote:
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engine block literally imploding.
Joe, make this happen.
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Old 11-13-2012, 02:50 PM   #10
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Excellent, thanks guys. Worrying for nothing. =)

Time to slap a turbo on!
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Old 11-13-2012, 02:56 PM   #11
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Quote:
Originally Posted by curly View Post
Joe, make this happen.
Convince Fae to design a crankcase ventilation system. He'll find a way.
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Old 11-13-2012, 10:20 PM   #12
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Quote:
Originally Posted by Joe Perez View Post
I'm still trying to imagine a scenario in which I would describe any amount of crankcase vacuum to be "excessive" short of the engine block literally imploding.
To be fair, the drag race guys that use vacuum pumps or dry sump setups actually do run vacuum regulators on the valve cover. Too much vacuum will cause issues with seals and such.

This is not what the OP is experiencing.
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Old 11-13-2012, 11:51 PM   #13
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