What does a bad pcv valve cause? - Nissan Forum
B11/B12/KN13 82-90 chassis B11 (1982-1985 Sentra), B12 (1986-1990 Sentra), and Pulsar

 
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#1 Old Sep 11th, 2002, 06:06 PM
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What does a bad pcv valve cause?

What problems would a clogged pcv valve cause? I tried changing mine cause it's caused with gunk along with the hose but I can't get the thing off myself so I need to go get it done at a garage. Would a clogged valve cause pinging possibly? I seem to ping even on hot days with 93 octane fuel. I have an all stock 90 b12 with 148,000 miles.
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#2 Old Sep 12th, 2002, 09:35 AM
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I'm no expert, but I found this web site recently: http://autorepair.about.com/library/ts/bl303a.htm. It describes common engine performance symptoms and their causes. The problem you're describing sounds like:

Quote:

There is a rattling noise from the engine when you accelerate:
Your car runs well all the time. But when you press on the gas pedal to accelerate or to go up a
hill, the engine rattles like the cylinders are full of marbles.

Possible causes:
1.The ignition timing may be set wrong: Adjust ignition timing.

2.The engine may be running too hot: Check and repair cooling system.

3.There may be a vacuum leak: Check and replace vacuum lines as required.

4.Incorrect grade of fuel: Fill with the correct, or higher, octane fuel.

5.There is an excessive amount of carbon built up in your engine: Clean carbon from
valves and combustion chamber. (Not a DIY job)

6.There may be a fault in the computerized engine control system: Check engine control
systems with a scan tool. Test circuits and repair or replace components as required.
(Generally not a DIY job)
This site explains some possible symptoms of PCV valve failure as:

* Engine uses more oil than normal, and there is (or is not) some smoke from the exhaust. <OR>
* Engine is using more oil than normal. Oil puddles under the car when parked:

It didn't give any other symptoms related to PCV valve failure. I'm sure there are some though.

Anyone else, feel free to dispute or confim this.

Jon
#3 Old Sep 12th, 2002, 11:55 AM
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The PCV valve is a simple ball check valve. It is oriented so that vapor flows from the cam/valve cover to the vacuum source, usually the intake manifold or tract. It has two failure modes:
  • Stuck open
  • Stuck closed
Stuck open would allow normal flow of crankcase oil vapor to the vacuum source, but would allow intake pressure pulses to flow back into the cam/valve cover. This could allow gasoline into the engine cases. Gasoline has almost no lubricating properties for high-pressure applications such as crank bearings and cam followers.

Stuck closed causes a slight power loss. The PCV valve has one major function and one minor side-benefit: it allows crankcase oil vapor to be burned instead of venting to atmosphere and the vacuum applied to the crankcase reduces crankcase pressure slightly. Pistons moving up-and-down pump crankcase air as wells as intake air, using horsepower to do so. Reducing the crankcase pressure reduces pumping losses.

Your pinging has nothing to due with the PCV; if it's gunked up and not rattling, that's an indication of badly worn rings and valve guides.

Bruce in Houston
'94 Nissan Sentra SE-R w/ $tuff, converting to ITA
'98 Suzuki Bandit 1200S w/ $tuff
'02 Dodge Dakota SLT 4-dr tow beast, stock!
#4 Old Sep 1st, 2010, 02:53 PM
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Hi everybody. I am trying with all my might to remove the pcv on my 91 sentra but it's not budging! I turned a little bit but any socket I can get it there wont move it and wrenchs are only damaging it!

91 Sentra :)
#5 Old May 18th, 2012, 08:03 PM
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Another thing that can happen (at least I think a bad PCV valve is the cause) is that your air filter compartment can fill with oil. I see no other way for oil to get into my '86 Pulsar's air filter compartment. The hose from the PCV goes right into the air filter compartment. I see no other entry except that this oil might be coming UP through the carburetor. I certainly hope that isn't the problem. Anybody got a guess on this one?

I'm hoping it's the PCV. That part is under $10. If the oil is coming up through carburetor, does anybody know where to get dynamite and how much it costs? That would fix it, forever and ever!
#6 Old May 18th, 2012, 08:32 PM
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A clogged PCV would cause excessive pressure to build up in the crankcase, which could cause seals to leak and oil to build up in the air cleaner. Another thing that can cause excessive pressure to build up in the crankcase is worn piston rings, which due to their poor sealing, would allow combustion gases to push pass the rings into the crankcase...more than the PCV system alone can normally vent.
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