If I had to formulate a brief opinion, I could write in one sentence – there are no problems.
At the same time, when checking Meta groups of interests and forums, replacement of the PCV valve is mentioned regularly. PCV valve is the most popular “damaged” element. How is that possible? Why do I use quotation marks? Read further!
Very concise about PCV:
a. functionality of the PCV: extract oil and fuel vapors and “send” them for repeated combustion;
b. functionality of the PCV valve: block the suction of oil and fuel vapors from the engine crankcase in its rarefaction modes (for example, in idle, when Valvetronic is not used);
c. localization of the PCV valve: upper part of the engine, valve cover, in the area of cylinders 5/6;
d. design of the PCV valve: rubber membrane, plastic valve.
In more detail, how the PCV valve works, you can read in other blog entries. This time, the most typical myths.
If you hear a hissing sound and other noises when opening the oil refill cap, the PCV valve is damaged – it has to be replaced.
FAIL. No, it is not true. Low airflow (and the accompanying noise) is acceptable. Even a completely new PCV valve tends not to close perfectly; there may be (and very often is) a microscopic grain of sand or other foreign object stuck in it.
If, when you open the oil filler cap, you feel a thinning (the cap is sucked in), the PCV valve is damaged.
Wrong. This test only confirms that the valve has not closed. At the same time, the inlet tract and the system of the crankcase are airtight: the membrane of the valve is NOT broken. Close the oil filler cap and do something useful!
If the car suddenly starts to shudder, white smoke appears from the exhaust, the PCV valve is damaged and has to be replaced.
Wrong. In 99% of cases, the reason for the white smoke is not the PCV or the injector, stuck in the open position (the second most popular victim of the “repair”). Correctly – check the PCV valve before any repair works.
This time, more about white smoke and the replacement of the PCV valve. Every time, when the white smoke is mentioned, in all possible communication channels, many “specialists” are ready for the diagnosis: defects of the PCV valve. The PCV valve is a long-lasting part; its defects are rare. The recommendation to immediately change it with such symptoms is unprofessional and completely unjustified. (I wanted to write – “completely dumb”, but decided not to traumatize a massive army of BMW users).
The cause of white smoke (if it’s not the water condensate – we talk of thick, whit smoke with a pungent smell): unburned fuel in the exhaust.
Typical reasons for unburned fuel:
a. the injectors stuck in the open position;
b. misfires.
Stuck injector. I singled out this defect separately because, in the case of such a problem, a very large amount of unburned fuel gets into the exhaust. Yes, of course, cylinder misfires are typical for the problem (as minimum misfires for the defective cylinder), but exactly the amount of fuel spilled in the exhaust distinguishes this situation from others, when some cylinder has misfires. It should be noted here that injector defects are very rare on these engines. Yes, the replacement of the injectors is practiced as soon as the smoke in the exhaust is detected (true though – less often, because the event is more expensive and special tools are required). In my practice, NO such defect has occurred (not for my car, not for the vehicles I have diagnosed). Yes, there has been a lot of white smoke. There was also no shortage of initial customer reports of injector defects. Unfortunately (or luckily), injector defects have never been confirmed. But, if you see that the smoke is thicker and more than you have ever seen, the fuel level in the fuel tank drops; the Rail pressure drops, it is possible that exactly this problem has appeared. Then there are not many options: trailer, service.
Misfires. Typical reasons for misfires:
a. The injector stuck in the open position (as mentioned before – very rare defect);
b. The injector starts to leak significantly (theoretical defect, have not seen myself, no approved case seen on the Internet);
c. Problems with the ignition. Worn-out spark plugs (including those contaminated with carbon). Ignition coils (especially: overheating of the ignition coils of cylinders No.5 and No.6 in idle). Very popular problems;
d. Incorrect fuel mixture. Problems with Lambda probes (for example, as consequences of misfires due to ignition problems); non-airtightness of the inlet tract (all possible seals, air tubes, PCV system), MAF, MAP, and other components;
e. Problems with fuel supply;
f. Problems with additional systems: VANOS, Valvetronic, etc.
As you can see from the list, PCV is only one of many possible options! And by my experience, ignition problems are to blame in 99% of cases of white smoke.
In this moment I already feel the counterargument of many service specialist – no, the ignition system causes misfires only in one/affected cylinder (it is unthinkable that suddenly several ignition coils or spark plugs would fail simultaneously), but there was white smoke, terrible twitching, error messages regarding misfires of several cylinders; at least 2 – 3 cylinders mentioned as misfiring! Subjectively, the engine was agonizing, as if the problem affected all cylinders! It was not possible to drive the car; the idle was a nightmare, too!
Unfortunately, there are several nuances:
a. These (as all others) Bosch DMEs have problems with the detection of misfires (the Siemens patent I have mentioned a lot), as consequences: error messages regarding misfires of several cylinders 140001 and 140010 are a “basic set”;
b. due to previously mentioned problems with misfire detection, almost always correctly working cylinders appear in the list of error messages; instead, the “guilty” cylinder very often is detected late or is not in the list at all (worst situation with the misfire detection – in idle and low torque driving conditions);
c. Due to a timely undetected cylinder, unburned fuel continues to get in the exhaust, the Lambda probes are “clogged”, as a result, the fuel mixture in all other cylinders is corrupted (using STFT, after a moment: rewriting common LTFT). The agony of all cylinders that have been working correctly until now begins.
d. If the car is kept in such/agony mode for 2+ minutes, DME damages LTFT and its correct functionality is not restored even after restart (logically – even by condition, that all nodes are working correctly).
My experience says – most of the time, minor problems (a misfire in the cylinder) lead to catastrophic consequences. The white smoke in the exhaust is only beginning. If the engine is not restarted immediately, after 2 to 3 minutes, the engine is not usable even after restarting. And then – unfortunately, only trailer. Yes, in the service, the problem would be solved by re-adapting the engine and prophylactic repair for the ignition system (cleaning or replacing spark plugs, replacing overheated ignition coils), but most often, the injectors are changed, and the subject of this topic is the PCV valve. The reason is simple – symptoms are harsh, error messages are a lot, and about many cylinders. Not even restarting helps. My suggestion – do not replace ANYTHING from the previously mentioned unless you have confirmation of the problems with that hub!
Returning to the PCV. If the engine of your car has “crashed”, even restarting does not help:
a. wait a little (5 .. 10 minutes). During this time, the spark plugs will dry, and the Lambda probes will “ventilate”;
b. Prepare ISTA, delete the error messages. Delete adaptations;
c. Start the engine. If the engine starts to work normally, allow it to idle for several minutes (it will ventilate the exhaust evenly). It is possible that there will be familiar white smoke from the exhaust – it is normal: the exhaust is flooded with fuel. Check Rough run in Call up functions or Expert mode, Rough run to confirm correct performance of all cylinders.
d. After several minutes, perform the re-adaptation of the engine (at first – adaptation of the flywheel, then creation of LTFT for different driving conditions);
e. Evaluate the misfires, try to identify the guilty cylinder by Rough run data (remember – misfire counter data can not be trusted)! If you do not manage to find the culprit, replace the spark plugs (if their resource is over 30 .. 40.000 km) or clean them (for 2 times for 5 minutes; perform Special procedure in ISTA). Replace the ignition coils of cylinders No.5 and No.6 (these ignition coils overheat when idling and, unfortunately, have to be replaced regularly).
If the engine after restart is still agonizing, perform initial checks:
a. In ISTA, call-up functions, see the fuel mixture data (they will appear several seconds after the start for a warm engine, as soon as the Lambda probe warms up);
b. If the fuel mixture is lean even after several restarts and deletions of the error messages, one of the reasons is the non-airtightness of the inlet manifold.
In this case:
a. Check the airtightness of all inlet connections;
b. block the PCV:
Disconnect the air tube [1] and press it closed on the side of the inlet manifold. If, after pressing the tube closed [1], the problems disappear, and the fuel mixture returns to normal, ONLY then repair the PCV. If the problems persist and the fuel mixture remains lean, the PCV is certainly NOT the cause!
