Exploring The Intake System of the CAEB engine

[edadelman]

This post is about misfires on the CAEB engine. I’d like to learn more about the relationship between the rear main seal, PCV and he intake manifold and what parts they play in causing misfires and poor engine performance. All input is greatly appreciated.


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I’ve now experienced misfires on two different TSI engines. One I fixed myself after replacing TWO PCV valves. The other was fixed after a shop replaced the rear main seal. I’d like to better understand the main seal failure and how it relates to misfires and rough running engines.

This seams like a huge Achilles heal for this otherwise pretty strong engine. What I’m struggling with is the main seal sucking in extra air intro the crank case. This air, I guess, comes up through the PCV valve and then back into the intake manifold where it combines with air from the throttle body which then creates too much air mass in the combustion chamber causing a lean condition and hence misfires.

Do I have this right?

If so, this seams like a flaw in the PCV. I assume the PCV only vents to the intake manifold and does so after it reaches a certain pressure to prevent over pressure in the crankcase. I assume that’s what the spring in the PCV regulates.

But if that’s right, then it’s regulating pressure that actually results in a vacuum condition at the main seal. So no over pressure occurring in the crankcase.

If this is the case, would a stronger spring in the PCV fix the problem?

I ask this because a PCV adjustment would be a butt load cheaper than a main seal replacement. I can deal with some oil on the ground (these engines seem to eat oil anyway). The misfires, however, are show stoppers.

So this entire intake system seems fragile but maybe it’s just my misunderstanding of it. I’d really like to know more about how the intake system regulates the air component of combustion. The fuel part seems pretty tight. The air side seems pretty fragile.

Again, Any thoughts or feedback would be greatly appreciated as I try to further understand these engines.

[Smac770]

The rear main might have gone on its own, or might have been toasted due to excess crankcase vacuum from a broken regulator diaphragm in the PCV.

EA888 Gen2 PCV overview.jpg

There are multiple different functions integrated here. At idle, the IM vacuum pulls crankcase vapors through the oil separators, creating the vacuum in the crankcase that pulls in fresh air from the turbo inlet. When boosting, the turbo inlet vacuum pulls crankcase vapors through the oil separators, creating the vacuum in the crankcase. As the IM is at positive pressure, it's cut off from the PCV system by the check valve. The pressure regulator valve limits the vacuum passed from whichever source to the crankcase to 100 mbar (white cap) or 20 mbar (black cap, old spec).

If the crankcase is under more than 100 mbar vacuum, the diaphragm in the regulator valve is likely torn and so the pressure difference between ambient and vacuum is no longer sufficient to counter the spring and close the gap to limit the vacuum exposure.

[redrackham17]

The rear main might have gone on its own, or might have been toasted due to excess crankcase vacuum from a broken regulator diaphragm in the PCV.

EA888 Gen2 PCV overview.jpg

There are multiple different functions integrated here. At idle, the IM vacuum pulls crankcase vapors through the oil separators, creating the vacuum in the crankcase that pulls in fresh air from the turbo inlet. When boosting, the turbo inlet vacuum pulls crankcase vapors through the oil separators, creating the vacuum in the crankcase. As the IM is at positive pressure, it's cut off from the PCV system by the check valve. The pressure regulator valve limits the vacuum passed from whichever source to the crankcase to 100 mbar (white cap) or 20 mbar (black cap, old spec).

If the crankcase is under more than 100 mbar vacuum, the diaphragm in the regulator valve is likely torn and so the pressure difference between ambient and vacuum is no longer sufficient to counter the spring and close the gap to limit the vacuum exposure.

Would appreciate your advice on this, what would the likely damage/results be of running the blacktop separator on a car that needs the white top? For the last 40,000 miles, my car has been driving with a black top AH PCV that was installed by the used car dealer I bought it from. However, the car is a 2014 2.0T with a CPMB motor (metal intake manifold), and I'm almost 100% certain it needs the white top AK revision. Have I been internally ruining my engine for the last 40,000 miles I've driven?

[Smac770]

Don't use the wrong PCV. The ECM is programmed with an expectation of how much air is being pulled into the intake manifold directly through the PCV, bypassing the throttle body, based on the crankcase vacuum. If you're using a black cap when you should have had a white cap, or vice versa, you're doing it wrong. Note, the black cap / white cap consideration is only valid for OE units; third-party units are subject to whether or not the third-party bothered with being consistent with OE units. All B8.5 motors are white cap; B8.0 might be black cap, black cap that are now running white cap (oil consumption stage one service; such as mine), or white cap originally.

The black cap runs a lower crankcase vacuum than white cap, so running black cap when you should have white cap won't mean much other than maybe a poor idle / misfires. It's the other way around that's more problematic, as changing from black cap to white cap requires an updated front main seal and ECM software. But there's no change in the rear main seal to adapt to the vacuum increase. The rear main seals are just known to separate sometimes. Just happens. Probably just got unlucky. My rear main has been running with white cap for nearly 165k miles, since it was replaced when they did the rings/pistons work.

The way you check for a leak in the engine that's passing unmetered air to the IM via the PCV is to pull the PCV to IM hose and cap it on the IM side. If the fuel trims and idle improve, then there was an air source in the engine, which could be a leak in the front timing cover or the rear main seal are common culprits. But I think that idea is a lot harder to do on a CPM with the metal IM, as the hose connection is just a little elbow there.

But yeah, you should have an AK on there. And don't waste your money on cheap third-party. Get the Audi OE or Hengst OEM (that's who makes the OE one) AK unit.

[redrackham17]

Don't use the wrong PCV. The ECM is programmed with an expectation of how much air is being pulled into the intake manifold directly through the PCV, bypassing the throttle body, based on the crankcase vacuum. If you're using a black cap when you should have had a white cap, or vice versa, you're doing it wrong. Note, the black cap / white cap consideration is only valid for OE units; third-party units are subject to whether or not the third-party bothered with being consistent with OE units. All B8.5 motors are white cap; B8.0 might be black cap, black cap that are now running white cap (oil consumption stage one service; such as mine), or white cap originally.

The black cap runs a lower crankcase vacuum than white cap, so running black cap when you should have white cap won't mean much other than maybe a poor idle / misfires. It's the other way around that's more problematic, as changing from black cap to white cap requires an updated front main seal and ECM software. But there's no change in the rear main seal to adapt to the vacuum increase. The rear main seals are just known to separate sometimes. Just happens. Probably just got unlucky. My rear main has been running with white cap for nearly 165k miles, since it was replaced when they did the rings/pistons work.

The way you check for a leak in the engine that's passing unmetered air to the IM via the PCV is to pull the PCV to IM hose and cap it on the IM side. If the fuel trims and idle improve, then there was an air source in the engine, which could be a leak in the front timing cover or the rear main seal are common culprits. But I think that idea is a lot harder to do on a CPM with the metal IM, as the hose connection is just a little elbow there.

But yeah, you should have an AK on there. And don't waste your money on cheap third-party. Get the Audi OE or Hengst OEM (that's who makes the OE one) AK unit.

Is this one a good idea? It's the same picture as the OEM one (which is $240 compared to $107) and I can make out that both are made by Hengst in Germany... https://www.fcpeuro.com/products/aud...ak#description

Also, I really appreciate the advice. I replaced the blacktop PCV the dealer put on 40,000 miles ago with a new black top, and the car ran smoother for a week or two before idling rougher, chugging more oil, etc. (this was 10,000 miles ago; I didn't know that I needed the white top because I thought that would require a ecm flash even though my car is a 2014). If you think the one I linked above is a good idea, imma buy it and put it on.

- - - Updated - - -

Don't use the wrong PCV. The ECM is programmed with an expectation of how much air is being pulled into the intake manifold directly through the PCV, bypassing the throttle body, based on the crankcase vacuum. If you're using a black cap when you should have had a white cap, or vice versa, you're doing it wrong. Note, the black cap / white cap consideration is only valid for OE units; third-party units are subject to whether or not the third-party bothered with being consistent with OE units. All B8.5 motors are white cap; B8.0 might be black cap, black cap that are now running white cap (oil consumption stage one service; such as mine), or white cap originally.

The black cap runs a lower crankcase vacuum than white cap, so running black cap when you should have white cap won't mean much other than maybe a poor idle / misfires. It's the other way around that's more problematic, as changing from black cap to white cap requires an updated front main seal and ECM software. But there's no change in the rear main seal to adapt to the vacuum increase. The rear main seals are just known to separate sometimes. Just happens. Probably just got unlucky. My rear main has been running with white cap for nearly 165k miles, since it was replaced when they did the rings/pistons work.

The way you check for a leak in the engine that's passing unmetered air to the IM via the PCV is to pull the PCV to IM hose and cap it on the IM side. If the fuel trims and idle improve, then there was an air source in the engine, which could be a leak in the front timing cover or the rear main seal are common culprits. But I think that idea is a lot harder to do on a CPM with the metal IM, as the hose connection is just a little elbow there.

But yeah, you should have an AK on there. And don't waste your money on cheap third-party. Get the Audi OE or Hengst OEM (that's who makes the OE one) AK unit.

Is this one a good idea? It's the same picture as the OEM one (which is $240 compared to $107) and I can make out that both are made by Hengst in Germany... https://www.fcpeuro.com/products/aud...ak#description

Also, I really appreciate the advice. I replaced the blacktop PCV the dealer put on 40,000 miles ago with a new black top, and the car ran smoother for a week or two before idling rougher, chugging more oil, etc. (this was 10,000 miles ago; I didn't know that I needed the white top because I thought that would require a ecm flash even though my car is a 2014). If you think the one I linked above is a good idea, imma buy it and put it on.

[RPMtech147]

nm...

[Smac770]

I would say the FCP Euro link should be a safe try. It appears to be a Hengst unit, and FCP's lifetime warranty makes an issue down the road less of a concern.

[edadelman]

I think I understand this. Only one of the two check valves is open at a time. Either the IM one at idle or the turbo side at boost. Either way, the idea is to create just enough vacuum to prevent a crankcase over pressure condition. Too much vacuum and pressure control valve shuts. Unless the diaphragm is torn I. Which case the vacuum pulls the main seal inward toward the engine eventually tearing it.

After that happens, the pressure control valve never shuts because now there is not enough vacuum to close (which I guess could mean that even if you replace the PCV with a brand new one it still won’t close.). Now the unmetered air entering the engine goes to the intake manifold. This happens both at idle via the intake manifold and at boost via the turbo. Too much air now goes into the cylinder and you get misfires.

Do I have this right?

[edadelman]

That’s what is puzzling me. A RMS causing misfires just didn’t make a lot of sense to me yet there is an awful lot of discussion about it. My journey began with the car misfiring horribly and blowing a lot of white smoke. I replaced the PCV with one as bought at O’Reillys. Everything seemed to run fine for about and hour and then the problem came back in full force. I pulled over (barely) and turned off the engine. After that it never started again. I had it towed home, did a lot of reading and then thought I might have a stuck injector. So I replaced them all. After that the engine started and would run but very rough. I ultimately replaced the PCV again and now it runs great. That was on the A4. No such luck on my Q5 which I took to a shop where I got the $2K RMS diagnosis. So I remain on this journey to better understand how all of these parts work together. This thread has been incredibly helpful in building that understanding.

[edadelman]

nm...

That’s what is puzzling me. A RMS causing misfires just didn’t make a lot of sense to me yet there is an awful lot of discussion about it. My journey began with the car misfiring horribly and blowing a lot of white smoke. I replaced the PCV with one as bought at O’Reillys. Everything seemed to run fine for about and hour and then the problem came back in full force. I pulled over (barely) and turned off the engine. After that it never started again. I had it towed home, did a lot of reading and then thought I might have a stuck injector. So I replaced them all. After that the engine started and would run but very rough. I ultimately replaced the PCV again and now it runs great. That was on the A4. No such luck on my Q5 which I took to a shop where I got the $2K RMS diagnosis. So I remain on this journey to better understand how all of these parts work together. This thread has been incredibly helpful in building that understanding.

[redrackham17]

For what it's worth, I swapped out my blacktop that I was wrongfully running on my B8.5 with a white top today. The car ran better, had a silky smooth idle even though it was a cold start after three days in 35 degree weather, and seemed to have a better throttle response (especially in second gear low speeds leaving a red light or stop sign). The low-speed pinging noise I've been dealing with this past month also didn't come back for a while, but I unfortunately noticed it when cruising after about a half hour of driving. Don't know if this helps anything that you're dealing with, but thought I'd share :/

[Smac770]

If you disconnect the hose from the PCV to the intake manifold, you're going to get lots of misfires and a rough idle. Because now the air into the intake manifold is way off from what the MAF is saying to expect.

This is the same thing when the diaphragm in the PCV tears, and you get that loud whistle because the intake manifold is now pulling in outside air through the vent hole in the PCV.

And this is the same thing when the seal on the RMS separates at the top, and you get the intake manifold now pulling in outside air through the RMS. The RMS can be leaking air but not yet be leaking oil. Easy enough to see, or should be, with a smoke tester on the crankcase.

But the real simple problem isolation step is remove the pipe from the PVC to the intake manifold and plug the intake manifold hole. Everything should be running just fine then. Or the issue is something other than unmetered air through the engine through the PCV to the intake manifold.

[edadelman]

If you disconnect the hose from the PCV to the intake manifold, you're going to get lots of misfires and a rough idle. Because now the air into the intake manifold is way off from what the MAF is saying to expect.

This is the same thing when the diaphragm in the PCV tears, and you get that loud whistle because the intake manifold is now pulling in outside air through the vent hole in the PCV.

And this is the same thing when the seal on the RMS separates at the top, and you get the intake manifold now pulling in outside air through the RMS. The RMS can be leaking air but not yet be leaking oil. Easy enough to see, or should be, with a smoke tester on the crankcase.

But the real simple problem isolation step is remove the pipe from the PVC to the intake manifold and plug the intake manifold hole. Everything should be running just fine then. Or the issue is something other than unmetered air through the engine through the PCV to the intake manifold.

Now I apologize in advance for what I know will be a crazy question. Let’s say you do plug the intake manifold and it runs great and lets also say the root cause ends up being the RMS. What would happen if you just permanently plugged the IM and let the PCV just vent to atmosphere? Rear main seals are expensive! :)

[Smac770]

With the IM separated from the PCV, there's no more source of vacuum for the crankcase, except when boosting. The fresh air breather function will cease, as it only operates when not boosting (IM under vacuum). But it might be fine enough for cost deferral. Eventually the RMS will finish coming apart and you'll have a nice oil leak all over in the bell housing. They did smoke test it to confirm the RMS, they're not just guessing at it? You're going to end up having to deal with it at some point. RMS is really easy, the work is removing and reinstalling the trans.

[edadelman]

Yes. Unfortunately smoke test confirms. I don’t have a lift so looks like I’ll have to take it to a shop where they can pull the transmission.