# What does a bad pcv valve cause?



## dschrier (May 6, 2002)

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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## Guest (Sep 12, 2002)

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:



> 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.
> 
> ...


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


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## bahearn (Jul 15, 2002)

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.


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## eclix (Jun 27, 2008)

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!


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## Lengo (May 19, 2012)

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!


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## smj999smj (Jan 1, 2006)

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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## fordlover666 (Apr 22, 2014)

*hey need help with a 89 ford f250 300 inline 6*

i a hve no oil pressure would that be from a bad pcv vavle


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## b13er (Apr 7, 2010)

No, as long as your car is full of oil and it's not leaking out everywhere, then it's safe to say that you have a bad oil pump.


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## Jesseb13 (Jun 25, 2016)

I've got a 93 b13 and she was my daily until some asshole slammed on the brakes. I have been trying to get her back going but if I can get the car started she'll run okayish for a few mins then sputter to death. There was oil on at least 2 plugs when I changed them a couple days ago..... what does this mean  this car is too cool to give up on my even if it looks like a pile. Anything helps!


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## smj999smj (Jan 1, 2006)

If it's on top of the spark plugs, inside the well, the spark plug tube seals have likely failed. Remove the valve cover and replace the valve cover gasket, tube seals and the little, rectangular PCV baffle gasket. You can get everything in one set except for the baffle gasket, which you have to get from Nissan (I'm assuming you have a GA16DE). It's part number 13271-4M501. BECK/ARNLEY 0361823 is a good kit to get that contains the gasket, seals and valve cover grommets.


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## slfaichnie (Sep 25, 2016)

Good Afternoon,
I am needing some urgent advice.

I own a a 2004 Nissan Presage 2.5l (QR25de motor) Auto.
Four weeks ago, I noticed it was running poorly. It has been running perfectly for the 3 years I owned it. it has 164k on the clock.
I took it to the mechanics and they looked into what was the issue. They found that I had a blocked Catalytic Converter and took it out. There is no need to have one in for NZ. 
I brought the car home, and noticed that is was a little smokey, i rung and they said that it was ok, it was normal as it was burning stuff from the exhaust. I asked for it to go back, and have an oil change. 
I brought it home after the oil change, and they had passed comment that the oil was sludgy, and that was probably the cause of the blocked converter. I drove 600kms in the car, and noticed that the smoke had not lessened, and also that the oil that they had put in, had disappeared. I rung and asked if they did put oil in, and they said yes, it was Castrol Magnatech 10w40. My specs ask that we use 15w30 and they said that it wasn't going to make a difference. I topped up the oil, with the 15w40 that I had, and continued to drive it. It wouldn't go one morning, and I had to call an Auto sparky, who plugged in a computer, and found the error code for a CPS sensor. This was replaced, and he passed comment that the CPS sensor was sludgy again. 

After some research, I found that a PCV valve, plays a very important part, and that this being faulty can cause the oil to be sludgy. I took it back to the mechanic and asked for them to replace this part. 
They rung to say, that yes, the mechanic has taken the valve out and you are correct that this part needs to be replaced. They would order one in. at this stage around 1000kms had been done, and around 6 litres of oil had gone missing in the car - assumed burnt)
Hopefully you have all kept up with me to here:

Now, the mechanic rings yesterday and says, that they have replaced the PCV valve in the car but when the started the motor up, the oil came out through the dipstick tube, and the air house/filter. they wore quite a bit of it and said they think they found the missing oil. 
They also run a compression test and some stage, and it was even. slightly low, but it was even. They didn't give me the figures, (but research shows that I supposed to have a result of 9.5:1) and also they have put the bore scope down the pistons, and they seem to all look fine. 
They took off a cover, and rung to say, that they want to look into it further now, and look at valve guides, and valve seals, and we could be looking at a replacement head, (10hrs of labour) or an engine conversion (10hours and $2500). We asked them to stop work on the car till we get some more information. 
My biggest question is:
That with the history that I have written above and the series of events, the PCV valve was the issue in the very first place. It should have been replaced immediately. It was probably the cause of the converter blocking and sludgy oil from the start. 
Now, my understanding is, that the PCV valve release pressure and the gas? that builds up, out of the crankcase. If this isn't working than that builds up. Wouldn't it be normal that with the installation of a new PCV valve, that the oil and pressure was released, and now that that has been done, give the engine a really good flush to remove as much sludge as possible, and change oil filter and put in clean fresh oil, and it shouldn't blow back again because the PCV will now work efficently?
We have also replaced all spark plugs, and two coils in the last 3 weeks of this all going on?
I just feel that we can't have done so much damage since we were on to it pretty fast, and that if we did what we suggested that the car may just run again. The mechanic hasn't done this, he wants to pull it apart to the head and look into further damage, cos his assumption is that that the oil has been pushed through the motor and already caused excessive damage, and he needs to investigate. I want him to put it back together, with a complete flush, new oil and see how it runs. It was a perfect car before 3/4 weeks ago, and never missed a beat - can we really have done that and technically blown up the engine in such a short space of time? 
I may be completely wrong and eat my hat if i do, but just feel that this is really excessive all of a sudden, and my total honest opinion is that they should be coping half the blame that they never picked up on the PCV valve to start with, from the blocked catalytic converter and never investigated into the sludgy oil. I basically told them to replace a part, that they didn't even consider. (I am quite pissy about that). My mechanic is no backstreet country hobo either, it goes to a Nissan Franchised mechanic where we pay over $100 per hour!!! 

Please leave any information that can help my situation, and whether you agree or disagree with my situation. I think i know my car, and read a lot about this motor, but I don' t feel i know enough to now tell the mechanic to put it back together, with a full service and drive it. I am needing a second opinion or advice on what to do next.

(Mother of four children, living in the counrtyside dream, needing my family car very urgently)


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## smj999smj (Jan 1, 2006)

Well, since the oil was already sludged when the PCV valve was removed, there's no way to tell whether the PCV valve was bad prior to the engine was sludged or if it was bad because of the sludge in the engine. In my experience with Nissan, it is very rare for a Nissan PCV valve to fail and the only two I have ever seen fail (in 16 years at Nissan) were on engines that were sludged due to lack of proper maintenance. You've owned it for three years, but there were nine years prior to that when it was owned by someone else. So, we have no idea what the service was prior to your ownership unless you have the previous owner(s) maintenance records. Another thing that can cause sludge is excessive blow-by past the piston rings, which is a possibility. 
I'm located in the USA, so, what problems we have here may or may not apply to your vehicle. In North America, the L31 Altima made its debut in 2002 with the QR25DE engine, which also found its way into the Sentra SE-R. 2001-2004 models had issues with burning a lot of oil; those engine specify 5W30. Originally, Nissan said it was because of the type of rings and they wouldn't always seat properly. Later, they said it was because of the ECM's fuel management software which resulted in the breakdown of the catalyst substrate inside the upstream catalytic converter, which is part of the exhaust manifold. In the QR25DE in North America, the engine does not use a conventional EGR valve system. What it does is use the variable camshaft timing to crack open the exhaust valve on the intake stroke to let inert exhaust gas get pulled in directly from the exhaust manifold. If the catalyst substrate was breaking down, tiny bits of it would get sucked past the exhaust valve and into the combustion chamber. This would score the cylinder walls and create a poor sealing condition between the cylinder walls and the piston rings, resulting in an oil burning engine. Nissan addressed this with a recall which called for re-programming the ECM software with an updated version, adding heat shields to the upstream catalytic converter, in some cases replacing the engine short block (and later, the long block) assembly and exhaust manifold/catalytic converter assembly. A lot of these vehicles were fixed, but there are still quite a few of them that show up on the forums complaining of high oil consumption. In most current cases, the vehicles are far out of warranty and/or the recall had already been done or the vehicle no longer qualifies for repair under it. Those vehicle owners usually end up replacing the engine with a reman or used engine or getting rid of the vehicle.
Whether any of this applies to the New Zealand QR25DE engines, I cannot say. It may be worth doing a little web searching for such incidents. What I would do is have a cylinder leakdown test performed on your engine to see if there is significant blow-by past the rings, into the crankcase. This would tell you if the engine is in need of replacement or complete overhaul or not. The fact that the engine is already sludged is not a good thing and may cause future issues, so, replacing the engine, or the vehicle, may make more sense in the long run. Good luck and keep us posted!


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