# Testing PCV Valve



## Altima SSS (Oct 10, 2007)

I'm sure some of you know that the PCV valve is buried under the intake manifold, and is almost impossible to change out. Those Nissan engineers should be whipped for a design like that.  

I noticed that the Owner's Manual maintenance schedule _does not address any service requirements of the PCV valve_, so maybe Nissan felt it was something that didn't need changing ... I guess it's possible.

Anyway, has anyone tried to test the operation of the PCV in place? I think I have a way to do it by removing the hose that goes from the rear corner of the valve cover to the main air intake hose (on a '93 & '94 model anyway) while the engine is running, and block the hose on the valve cover side with your finger to see if there is a suction on the hose. If there is a suction, the the PCV is not blocked. The engine should also run slightly differently when you block the hose and then unblock it with your finger as the flow going into the intake manifold will change some. Flash light required to see it well.

If you wanted to get fancy, you could have a helper do the hose blocking/unblocking and then listen to the PCV with a stethoscope. If you look real hard down from the top on the passenger side of the intake manifold, you can barely see the end of the PCV where it screws into the oil separator housing. 


I plan on doing this little test in the next day or so ... will let you know what I find.


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## xgrave (Aug 11, 2007)

ive tried to see how to remove it, but it seems like the easiest, but i mean easiest, way to do it is to remove the intake manifold...

in terms of testing it, ive read that if you blow into it (NEVER inhaling the gases it may have come in contact with) works too, or if you shake it and hear a rattle then it should be fine otherwise replace....my 2 cents


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## Altima SSS (Oct 10, 2007)

xgrave said:


> ive tried to see how to remove it, but it seems like the easiest, but i mean easiest, way to do it is to remove the intake manifold...[/auote]
> 
> I read in a manual somewhere for the 2.4L, that taking just the intake manifold off is very difficult because of some hidden bolts that are hard to get to. The manual recommended taking the head and intake manifold off as an assembly !  This car isn't very easy to work on when major work is involved.
> 
> ...


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## Altima SSS (Oct 10, 2007)

I did the PCV valve test tonight, and here are the steps for 93 and 94 Altimas ... not sure about 95+ models:

1) Start engine and let it warm up to normal operating temperature.

2) Locate the hose that runs from the rear corner of the valve cover to the engine intake air tube. Remove the hose from the engine air intake tube. Pliers will be required to release the spring clamp before pulling the hose off the fitting.

3) Block the port on the air intake tube with your finger. This step probably isn't necessary, but if it's not plugged the engine will be getting more air than what the mass air flow sensor thinks it's getting. The engine will probably still run anyway.

4) While the engine is running, put a finger loosely over the removed hose that goes to the valve cover. You should feel slight pulsations on the hose. This is an indication that the PCV is operating correctly.

5) Tightly cover the end of the hose with your finger and wait about 10 seconds, then remove your finger. You should feel a pretty strong vacuum, and also hear air rushing into the hose because of the vacuum built up during the 10 seconds of hose blockage. This is basically steps 5 and 6 in the AutoZone link in the post above. This means the PCV valve is working correctly.

6) While blocking the end of the hose with your finger, rev the engine upto about 2500 ~ 3000 RPM. Either have a helper rev the engine, or rotate the throttle by hand where the throttle cables connect on the engine. The vacuum level on the hose should be less than when it was at idle. This is because the vacuum level in the intake manifold is less, and there is also more engine blow-by occurring. This is normal, and indicates the valve is working correctly.

7) Turn off the engine, and reconnect the line that was removed from the intake air tube.

If the PCV valve was clogged, there would be no or very little vacuum produced during step 5 above, and you wouldn't feel any pulsations during step 4 above.

If you keep your oil changed regularly, and don't do a ton of very short drives (where the engine doesn't warm up much), then I think the PCV valve would stay clean and operate correctly for a long time. Maybe this is why Nissan doesn't even show it in the mainteance schedule in the Owner's Manual.


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## Altima SSS (Oct 10, 2007)

Altima SSS said:


> I'm going to use the running engine to 'suck' through the valve. It should give it a test similar to this ... see Figure 2.
> 
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BTW ... what's shown in Figure 2 in the AutoZone link above can not happen since the intake manifold sucks on the end of the PCV valve where they show the finger touching. The test they talk about could only work if the suction was on the other side of the PCV valve, which it is not. 

You have to watch these manuals sometimes, as they are not always correct. :lame:


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## xgrave (Aug 11, 2007)

i hear ya...man you'd think a manufacturer would try to make things so that they are easy to service...at least the ones that need frequent services...very lame, hope everything goes well...have you tried under the car?


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## Altima SSS (Oct 10, 2007)

xgrave said:


> i hear ya...man you'd think a manufacturer would try to make things so that they are easy to service...at least the ones that need frequent services...very lame, hope everything goes well...have you tried under the car?


I've looked at every angle ... there's no way I'm going to even try to change the PCV valve. Do a search, and you'll find where a few guys have done it, but it took about 4 hours to do it.

Based on the 5 minute test I did above, the PCV valve in my 94 seems to be working OK. Seems strange that Nissan doesn't even address changing the PCV valve in the owners manual maintainance schedule. Maybe it just doesn't fail under normal conditions.

I had bought a new one from NAPA, and it's all metal construction, so maybe it never wears out. Took it back for a refund since I'm not going to even try to install it.


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## xgrave (Aug 11, 2007)

true! i bought one and the sucker is still sitting in my tool box...i dont even know what to do about it and once thought about taking out the intake manifold but man that would take me one weekend which i dont have right now since school and work are on...but some day...lol...btw how did you reach the hose? i was trying to see how to test it too but i see no way of reach the hose...???


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## Altima SSS (Oct 10, 2007)

xgrave said:


> true! i bought one and the sucker is still sitting in my tool box...i dont even know what to do about it and once thought about taking out the intake manifold but man that would take me one weekend which i dont have right now since school and work are on...but some day...lol...btw how did you reach the hose? i was trying to see how to test it too but i see no way of reach the hose...???


I didnt' test it at the hose that goes right on the PCV valve, but the hose that goes from the valve cover to the air intake tube. On my 94 (and your 93) there is a large hose that goes from the valve cover's rear left hand corner to the intake tube. In the figure below, make note of the "Fresh Air" and "Blow By Gas" arrows indicating direction of flow.










This hose is the fresh air tube shown in the figure in the AutoZone manual link. When the PCV valve sucks crankcase vapors out of the engine, then fresh air is drawn back into the engine through the valve cover hose. If the PCV valve wasn't working or clogged, then you wouldn't feel any suction on that fresh air hose. Re-read my test steps and look at the AutoZone manual figures and you'll see what I'm talking about.

I forgot to also mention that if the PCV valve is clogged or not working correctly, that there could be some pressure build-up inside the engine. One indication of this would be the dip stick constantly being popped out of it's tube, as it would most likely pop before anything else like a gasket or seal.


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## metronet (Dec 12, 2005)

Thank you Altima SSS for this great guide on how to test the PCV valve


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