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2011-2016 Cruze 1.4L PCV System Explained


Video:
I made a video to help better explain how this whole PCV system works to supplement this article.

Overview:
The purpose of this post is to explain the function of the PCV system in the 1.4L Turbo engine so those of you who are having issues or trying to help people have some idea of what is going on and where to look for potential trouble spots. We will start by assuming you know what a PCV system is designed to do. If not, stop here and go to google. Return when you understand the basics of what A PCV system does. Basic mechanical knowledge is required. I will attempt to explain this by walking you through the path of the PCV system. Below is an outline of the whole system and the direction the PCV gas flows, and each step will include any pictures I could find that show the actual component described. The terms "non-return valve" and "check valve" are used interchangeably. A check valve allows a gas or liquid to move in one direction but not another.




1 We start with the crankcase that has built up pressure, under a normal operating vehicle. We exit the crank case through the cylinder head at the two long ports at the bottom of the following image.

2. Those two ports feed into the valve cover, at the two long ports on the right side of the image below.



3. From there, we travel through a baffled oil separator system. THIS IS WHY WE DO NOT NEED A CATCH CAN. This pathway inside the valve cover is tasked with separating oil vapor from the PCV gas traveling through it. From there, we exit into the small port on the left (refer to arrow at the left of image above), to go back into the cylinder head. Notice the corresponding port on the cylinder head (arrow at the top of the image)?



4. Next, we find ourselves in the intake manifold, which is pictured below. Inside this port, there is a check valve (which GM refers to as a non-return valve), pictured in the next two images. Note, this is not a ball (as it has been previously referred to). It is a non-return/ check valve, that more closely resembles a specifically shaped nipple.




5. A corrugated hose comes out of the intake manifold, which has an open path from the PCV system and does not have to go through the non-return valve.

6. We arrive at the top of the below image, where there is ANOTHER CHECK VALVE.



7. Lastly, we exit to the turbo housing at the turbo's inlet (see oil streak above).

In case you missed it:
The crankcase is under vacuum whenever the engine intake is under vacuum; the check valve valve in the intake manifold opens and pulls all crankcase gases while keeping the check valve at the turbo inlet closed. When the engine produces boost in the intake (during acceleration or uphill driving), that check valve closes due to the air pressure inside the intake manifold, because we don't want to pressurize the PCV system. When this happens, the extra crankcase pressure is relieved through the check valve at the turbo inlet. PCV gas at the intake manifold check valve flows into the intake manifold but not back into the PCV system, and air at the turbo inlet housing flows into the turbo inlet, but not back into the PCV system. Both check valves allow PCV gas back into the intake; one before the turbo and one after the turbo. I want to make sure this is clear.


When things go wrong:

What happens if the check valve in the intake manifold fails (Step 4)?
  • Excess vacuum is produced on the PCV system internals when intake is under vacuum, which may pull more PCV gas than the oil separator is capable of filtering. Excessive intake vacuum may be applied on the crank case, which may also cause premature failure of the regulator diaphragm.
  • Boost is leaked from the intake manifold into the PCV system. You may not notice this happening until more symptoms show up. The boost leak seems to overwhelm the flow capacity of the check valve at the turbo inlet, and causes positive crankcase pressure. This positive crankcase pressure then causes the turbo to leak oil internally, the CPASV seals to leak, the oil pan gasket to leak, and oil to trip from the throttle body at the connection to the intake tube.
  • Excess positive crankcase pressure caused by the boost leak will cause the burst disk in the valve cover to rupture. Since the check valve itself may not show any other symptoms of failure, you may find yourself constantly replacing intake manifolds until you address the root cause.
  • In the event that the turbo inlet check valve is stuck in addition to the intake manifold check valve disappearing, oil consumption will increase. See below under "if you are burning oil."
Notes: The intake manifold check valve can either disappear completely due to fatigue (it's rubber after all) and be ingested by the engine through the intake, or it can be stuck open. To inspect this check valve, pull the corrugated hose off of the intake manifold, and shine a light in there. If you see nothing, dip a cotton swab in rubbing alcohol and clean the side facing the vehicle's firewall as far down as you can since it may just be dirty. If there is still nothing there, your check valve is gone. IMPORTANT: failure of the check valve does not automatically result in elevated oil consumption.

What happens when the check valve at the turbo inlet fails (Step 6)?
  • In the event that the check valve at the turbo inlet is stuck closed, the burst disk can fail.
  • Excess pressure will build in the crank case, which will prevent the turbo bearing housing from draining oil, and will seep oil past the turbo seals to be burned in the exhaust or through the intake. (Walker Morgan noted this one). In the event that this occurs, oil consumption will increase.
Notes: If you are burning oil, remove the corrugated line and blow into it. If it does not blow freely, your check valve is stuck closed. Wipe the oil from your mouth, and replace it. A second possibility is an intake manifold gasket failure around the PCV ports in the first picture above.

What happens when the PCV regulator diaphragm (Step 8) fails?
  • Excess vacuum or boost produced on the PCV system by the intake manifold check valve (whether or not it is good) being open will cause unmetered air to flow through the vent on the cap and may trigger a check engine light. Refer to "related service codes" at the end of this article. You will hear a hissing sound in the engine bay.
  • If the either of the above check valves have failed, you may find oil vapor sprayed in the proximity of the cap vent.
Notes: The PCV regulator diaphragm may fail from fatigue, or it may fail in the event that either of the PCV check valves fail and cause excess vacuum or excess PCV pressure. A failed PCV regulator diaphragm may or may not be a symptom of another root cause.

What happens when the corrugated hose fails?

- The corrugated hose may crack and develop a vacuum leak. If this happens, unmetered air will enter the the intake under vacuum when the intake manifold check valve is open. If severe, this may trigger a check engine light. Refer to "related service codes" at the end of this article.

What to do if these components have failed:
http://www.cruzetalk.com/forum/129-gen1-engine-transmission-tutorials/49665-how-replace-valve-camshaft-cover-1-4l-turbo.html
No tutorial currently exists for replacement of the intake manifold, the corrugated hose, or the turbo inlet check valve. Any volunteers?
- I've presented a retrofit solution for the intake manifold check valve failure in the following thread that will cost 1/2 to 1/3 that of a new intake manifold while lasting much longer:
http://www.cruzetalk.com/forum/34-gen1-1-4l-turbo/189402-2011-2016-cruze-1-4l-turbo-intake-manifold-pcv-check-valve-fix.html

Related Service Codes:
P0106 P0171 P0299 P0507 P1101 P2096
 

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Discussion Starter #4
De we have any idea of what type of check valve is used at the turbo, and what it looks like viewing through the connection of the corrugated tube? Wondering if this check valve could be cleaned and inspected without removal of the turbo.

I've seen something similar to this over on the sonic forum, but this is the first time someone has mentioned two check valves in the PCV system.
I don't have a picture, but if someone wants to pull theirs off and take a picture of it, I can post it. Don't know the answer to your other questions yet.

I haven't yet seen an article on SOF that goes into as much detail as I did here and you really have very little analysis ability if you don't even know there are two check valves. It took a fair bit of research for me to get this far.
 

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Great write up! It really cleared up my understanding of our PCV system! With this new understanding though I'm now wondering why when someone has a PCV problem you usually only hear of them replacing the valve cover (burst disk), and GM has extended the warranty on it. Seems like its most likely that one of these other valves have failed causing the burst disk to fail.
 

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Nice write up! Thanks for taking the time to write this explanation.

Makes me realize how important it is to use good oil and good gas. Our 2007 Mazda 3s has 105,000 miles on it and still has the original PCV valve and doesn't burn any oil (PCV valve is hard to change because you have to take off the intake manifold to get to it - genius) and I have 50,000 miles on my 2011 1LT Cruze and still have the original PCV valve and I have never used any oil between changes. (knock on wood - hand hitting head :) I can still see the check valve in the intake manifold - yeah). All our cars are about 80% city driven. Not totally stop and go but not highway driven either. I try to take our cars out the weekend and drive them at highway speeds for about 10 or 15 minutes.
 

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Great write up! It really cleared up my understanding of our PCV system! With this new understanding though I'm now wondering why when someone has a PCV problem you usually only hear of them replacing the valve cover (burst disk), and GM has extended the warranty on it. Seems like its most likely that one of these other valves have failed causing the burst disk to fail.
Note that some of these can be failing from burst disk fatigue since the crank case is constantly under changing pressure, so you can't assume that every time one fails, that there's an underlying root cause.

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Great write up! It really cleared up my understanding of our PCV system! With this new understanding though I'm now wondering why when someone has a PCV problem you usually only hear of them replacing the valve cover (burst disk), and GM has extended the warranty on it. Seems like its most likely that one of these other valves have failed causing the burst disk to fail.
To my knowledge GM has not created an extended warranty for the PCV system like they have for the water pump, and battery cable. I've been under a rock for the past few months, if anyone has details of a extended separate campaign like the water pump please post details. The powertrain warranty covers the intake and the valve cover provided your car is still under powertrain coverage.

I think a lot of people are doing the valve covers first, as they are easy, but it's probably the case that the intake missing the check valve is what's causing the valve covers to burst. If your driving style and conditions are right, maybe you can drive for quite a while with a intake check valve missing. "UpstateNY" or something like that is on his third valve cover, and he has no check valve in the intake. With the high mileage on his car he has decided not to address the check valve issue.

To my knowledge the intake is only available loaded with the throttle body and new injectors. A $280-300 part. When will the aftermarket start supporting intakes with check valves for this car? Or better yet a replacement check valve.

I know GEN 2 1.4's use a different system. Hopefully it's not this problem prone..
 

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Discussion Starter #10
To my knowledge GM has not created an extended warranty for the PCV system like they have for the water pump, and battery cable. I've been under a rock for the past few months, if anyone has details of a extended separate campaign like the water pump please post details. The powertrain warranty covers the intake and the valve cover provided your car is still under powertrain coverage.

I think a lot of people are doing the valve covers first, as they are easy, but it's probably the case that the intake missing the check valve is what's causing the valve covers to burst. If your driving style and conditions are right, maybe you can drive for quite a while with a intake check valve missing. "UpstateNY" or something like that is on his third valve cover, and he has no check valve in the intake. With the high mileage on his car he has decided not to address the check valve issue.

To my knowledge the intake is only available loaded with the throttle body and new injectors. A $280-300 part. When will the aftermarket start supporting intakes with check valves for this car? Or better yet a replacement check valve.

I know GEN 2 1.4's use a different system. Hopefully it's not this problem prone..
No warranty to my knowledge. That would be news to me as well.

Anyone who replaces the valve cover should at least inspect the check valve in the intake manifold.

Theoretically, you can plug up the check valve port in the intake manifold if it disappears (with epoxy), and all of your PCV pressure would be vented to the turbo inlet. However, that also means that you'll be coating your intercooler with the same oil streak that you see at the turbo inlet.

You can pick up that intake manifold from ebay with injectors and all for about $200. It's not much of a discount but it beats $300. An aftermarket option can't come too soon.

The check valve cannot be replaced without breaking the seam on the intake manifold and gluing it back together. It's not an option.
 

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Great write up! It really cleared up my understanding of our PCV system! With this new understanding though I'm now wondering why when someone has a PCV problem you usually only hear of them replacing the valve cover (burst disk), and GM has extended the warranty on it. Seems like its most likely that one of these other valves have failed causing the burst disk to fail.
OK, maybe I'm wrong... I thought I had gotten one of those letters from GM extending the warranty on the valve cover. I'll look through my stuff, if not we can deduct from my credibility points:)
 

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I really Hope My orginal PCV valve goes bad before my 5 year warranty expires one year from now...I'm only at 35,000 miles will be 45,000 by next summer..
 

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I really Hope My orginal PCV valve goes bad before my 5 year warranty expires one year from now...I'm only at 35,000 miles will be 45,000 by next summer..
They aren't that expensive to replace even if you have the GM dealer do it. The part is like 50 bucks and it is real easy to get to so the labor shouldn't be too bad.
 

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I like that part of using epoxy to plug hole if valve is missing in the intake. Any chance of doing a PCV delete? Its crossed my mind.
 

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I like that part of using epoxy to plug hole if valve is missing in the intake. Any chance of doing a PCV delete? Its crossed my mind.
You'd have to plug up that port to do a PCV delete, but theoretically you could, as long as the EPA doesn't find out.

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Deleting wouldn't be any worse then running without cats. If I were to do the delete Im not sure if the pcv hose from intake can be ran to a catch can and vented to the atmosphere and then plug the turbo intake end of hose. If epoxying the intake manifold where valve would be missing would that cause the crankcase to no longer be under a vacuum? If my nipple valve goes missing again and oil collects at the TB and out of 5y/100k PW I will be doing this instead of replacing whole intake manifold assembly.
 

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Deleting wouldn't be any worse then running without cats. If I were to do the delete Im not sure if the pcv hose from intake can be ran to a catch can and vented to the atmosphere and then plug the turbo intake end of hose. If epoxying the intake manifold where valve would be missing would that cause the crankcase to no longer be under a vacuum? If my nipple valve goes missing again and oil collects at the TB and out of 5y/100k PW I will be doing this instead of replacing whole intake manifold assembly.
I don't know of any oil vapor that the catch can would catch, that the valve cover doesn't under normal operation. Every catch can I've seen installed on these cars does nothing but accumulate moisture, and a good baffled catch can would run you well over $150 for little to no real benefit. In a 15,000 mile oil drain interval (with AMSOIL signature series), I didn't consume any measurable amount of oil (the line on the dipstick was the same).

Closing off the intake manifold would cause the crank case to no longer be under vacuum. I don't think that would affect anything though. I'd be tempted to do the same thing if the intake manifold failed if there isn't an improved aftermarket solution.
 

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Wasn't referring to having a catch can part of the loop. Would leave outlet hose of can open to the atmosphere. Maybe using a breather filter at end of intake manifold hose would work without the need for a catch can.
 

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Deleting wouldn't be any worse then running without cats. If I were to do the delete Im not sure if the pcv hose from intake can be ran to a catch can and vented to the atmosphere and then plug the turbo intake end of hose. If epoxying the intake manifold where valve would be missing would that cause the crankcase to no longer be under a vacuum? If my nipple valve goes missing again and oil collects at the TB and out of 5y/100k PW I will be doing this instead of replacing whole intake manifold assembly.
Crankcase would not be under vacuum any time you were under boost (so basically all the time in these cars). Great way to blow out all the other seals in the motor.
 

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There is vacuum at idle. Pull oil dipstick.
I guess my ? is what happens with pcv system while in boost.
 
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