CCV of turbo engines

In this entry – how the BMW shoot themselves in the foot. Again. Something regularly goes the wrong way in this reliable company. Besides, it happens so brightly that seems BMW AG consists of two departments. One of them is in the Avangard of the technical development, but the second one works with a Motto “how to break everything, which is good”.

Without illusions – during the next few years, Internet forums will be full of topics regarding N20/N26/N55/B48/B58 and other engines of this engine family. The main symptoms, which will be discussed:

  • intense shivering of the engine in idle, even shutting down; particularly severe – for the cold engine and/or engine directly after staring (during the first minute);
  • the error messages regarding lean (less often – rich) fuel mixture;
  • misfires;
  • problems with passing TI due to the results of the exhaust gas tests.


But – for everything in a row.
As the title of the topic suggests, the central part – CCV. If you read the descriptions of these turbo engines, the CCV section will not be the most natural part to understand. When reading, for example, the description of CCV of the N20 engine, the feeling, that the persons, who created the description, did not get the topic for themselves, is not leaving me.

The performance of the CCV of the BMW turbo engine (simplified) can be described in the following way:

  • when the engine runs in idle and in a range of low speed + low load (there is a depression in the inlet manifold – Normally Aspirated mode), the crankcase gases (as for the atmospheric engines) are sucked from the crankcase to the inlet manifold;
  • when the engine runs with higher speed and/or in higher load, the pressure is created in the inlet manifold (Turbocharged more – the turbocharger starts to work), so suction of the fumes to the inlet manifold is not possible anymore. To avoid the excessive pressure in the crankcase, the valve, which stops the air intake in the wire “crankcase/inlet manifold,” becomes operative;
  • when the engine works with higher RPM and/or load, in the air channel before the turbocharger, the air depression is created. This pipe is used for the mode when the ”usual” suction of the fumes is not possible. In this mode, the air valve which allows sucking the oil fumes from the crankcase via this pre-turbine air duct opens.

Sounds very simple and understandable! So it is!

Here, the CCV of the turbo engine in the cross-section:

In the image:
No.8 – the valve, which closes in mode, when the extra air pressure appears in the inlet manifold;
No.2 – the valve, which opens when the depression is created in the pre-turbocharger air duct.
Both these valves are an upgrade, comparing to the classic CCV and are intended directly for driving conditions of average/high load and/or average/high RPM’s.


While both these valves work entirely – there are no problems. The situation changes once the leakages in the valves appear.

  • If the leakage is in the valve No.8, part of the air gets in the crankcase, then via valves No.3 and No.2 back in the pre-turbocharger air duct. Part of the air, measured (planned) by DME, “disappears” and doesn’t gets to the cylinders. It can cause problems with multiplicative type fuel adaptations. They will be relatively negative; it means – DME will try to reduce the amount of fuel. Or, how INPA/ISTA displays this situation for these engines, LTFT in a medium torque mode will be <1.00 (1.00 is in a perfect situation).
  • If there is a leakage in the valve No.2, the situation becomes even more dramatic. In Normally Aspirated mode, unregistered and unnecessary air gets in the intake manifold, completely disrupting the proportions of the fuel mixture. This problem is exceptionally particular in the idle.


Besides, this problem has characteristic nuances:

  • during the first minute after starting the engine (while the Valvetronic is not activated), problems will be more particular because the depression in the intake manifold is stronger;
  • manifestations of the problem will change after 15 .. 40 seconds after starting the engine (or directly after restarting the engine), as soon as the air mass meter and the wideband probe(s) reach the ”lights off” mode. At this moment, DME will detect the non-compliance of the fuel mixture and will try to fix the situation;
  • in case of severe damage to the valve No.2, there can be problems with starting the engine. A too high amount of the air can create such a lean fuel mixture, that the fuel will not ignite. It is possible that after a few unsuccessful starts, DME will turn on the Valvetronic directly in the moment of the start of the engine (to reduce the problem of too high air amount). Still, the engine will work very unstable in this mode.


Has the BMW AG intended the replacement of this valve No.2? Of course, not! The valve alone can not be replaced; the whole valve cover should be replaced.
Has the BMW AG in any way done the work if diagnostics specialist easier, anticipating the diagnostics of such defects of CCV? No, directly the opposite!

  • if for older engines (N54/N55) the crankcase ventilation pipe was still available (it was possible to block it mechanically), for newer engines (N20/N26/B48/B58) the air duct to the inlet manifold is created in the block of the engine, and it is not possible to block it;
  • even if we choose to block the air duct, which goes to the pre-turbocharger air duct, the problem appears: in a mode of the average load/torque, valve No.8 does not work anymore as intended; the pressure in the crankcase will be increased. Accordingly – blocking of the 2-nd valve fits only for a short test of idle, but does not fit for, for example, the re-adaptation of the engine and full functionality test;
  • nor INPA, neither ISTA displays the Offset type LTFT or Integrator(s). Both parameters are critical to understanding if the DME can maintain the fuel mixture in idle;
  • for the modern (with it understanding the N20+ engines), the additional optimization on costs of EUR 10 has been made. This would be the price of the fuel pressure sensor if the amount of the order to the manufacturer would be several million units. These engines don’t have the LP fuel contour pressure control anymore. Accordingly – there is no possibility to control this contour, and also the doubling function of the HPFP pressure control is lost. The result – to make sure that the fundamental fuel problems are not caused by, for example, the strong fluctuation of the LP contour pressure or the issues with the HP contour pressure sensor, the old-school method – manometer – should be used.

Thanks to these upgrades, we are back in the 30 years old past. The LP contour fuel pressure should be controlled by the manometer, CCV should be replaced by the suspicion that the valves are leaking. Because there is no correct solution on how to check the airtightness of the system.

To create severe problems with the fuel mixture in idle, it is enough with a hole of 1mm in the intake manifold! Accordingly – it is enough for a grain of sand to stuck in the 2-nd valve for the problems to be guaranteed! Besides, the manifestations of the defect could be quite strange.
When DME detects a lean mixture (as if by the correct position of the throttle), it will increase the amount of the fuel in cylinders. A more significant amount of fuel in cylinders will increase the mechanical efficiency of cylinders – RPM of idle will increase. When detecting the rising of the RPM in idle, DME will swiftly reduce the opening of the throttle and (proportionally) the amount of fuel. The reduction of the opening of the throttle will upset the already delicate balance because the air intake happens to bypass the throttle. The fuel mixture will become unexpectedly lean again. The fuel amount will be increased swiftly – again. As a result, the RPM in idle will fluctuate, all other parameters of the system – Lambda, air mass, mechanical efficiency of cylinders – will fluctuate so strongly that it will be hard to understand, which setting is correct at all! Because none of them could be right!

To even more “facilitate” the work of the diagnostic specialist, the Lambda data of these engines is not available! To be honest, I don’t understand such a thing anymore. How could it be, that the primary parameter, which describes the fuel mixture, is not available?
Instead of Lambda value, the “Voltage” parameter is available… Without any explanation.

Short info regarding ”Voltage” vs. Lambda.
Bosch DME Lambda = 1.00 corresponds Voltage = 1.50 V
Rich mixture: Voltage < 1.50 V
Lean mixture: Voltage > 1.50 V

More comprehensive information: in the entry regarding Bosch ADV Lambda sensors.

Most probably, you will say – you know only how to criticize. No, I also have suggestions. In no way, I would create the CCV system in such a way! In my opinion, one of the solutions: in all driving conditions, suck the crankcase gases to the pre-turbocharger air duct. To create the necessary thinning in this air duct, use the flow converter, which is successfully used, for example, for the pumping of the fuel in the fuel tank (using EGR contour). My apologies if any of the manufacturers are already using such a principle – I don’t claim the originality of the solution.

To the diagnostics specialists, I suggest purchasing one piece of the CCV ventilation pipe (a pipe, which connects the CCV with a pre-turbocharger air duct) for each engine model. Block this pipe, using, for example, Makroflex. Such a pipe will allow you quickly to indicate if the engine is sucking the air via valve No.2. If the diagnosis is confirmed (the fuel mixture changes swiftly – it will become rich for a moment, fluctuation of idle and shivering disappears) – unfortunately, all valve cover should be replaced.


In the end.
I have suspicions that a very prudent person is working at a very responsible position, With a large “inertia” of making decisions. How to otherwise explain the following:

  • 3rd valve of the CCV system of the N20 engine can be replaced separately;
  • the same valve of the CCV system of the N26 engine can not be repaired, BMW AG especially emphasizes it in the educational materials.

Obviously, when creating the CCV of the N20 engine, BMW AG took into account the experience of previous (atmospheric) engines – the CCV membrane was the weak spot of the system. Now it turns out that the valves No.2 and No.8 of the CCV of the turbo engine cause much more significant problems – the wrong spare part is created as replaceable. What did the BMW AG do? Gave up the concept or the repairable part – let the owners of BMW regularly replace that piece of plastic with the costs of several hundreds of EUR! Why not, if there are no other options?