The topic of this entry can be guessed by the name of it. So – there is no intrigue. I’ll go straight to the technical information.
This problem is typical for N43 series engines (more than 10+ cases identified), but no cases with N53 series engines so far.
Symptoms of the problem:
a. low quality idle in Homogenous mode (chaotic additional vibration, shivering without misfires) or permanent and unsolvable vibration in Homogenous mode (the culprit cylinder with the reduced efficiency identified, but replacing injector and re-adaptation does not help). A Stratified charge was restored, and it goes without saying;
b. idle in Stratified charge – correct, problems disappear never been there;
c. all live and adaptation data – correct;
d. the error message 2D06 Air mass system. Air mass – too high (zu hoch) recorded.
Here is the example – freeze-frame of two different vehicles/engines:
Short info on each of the cases:
a. in the first case – the car had unsolvable reduced mechanical efficiency of cylinder No.3 in Homogenous mode (../F5/F7; cylinder efficiency around +40 .. 60 units, which means the efficiency is lowered of around -30 .. 40%);
b. in the second case – in idle, all cylinders are working more or less equally (+/-10 ..30 units relatively), but the idle quality is poor, and there is no way to fix the error message (new MAF, Lambda probes, etc. installed).
From the error message freeze-frame, we can guess that the airflow data are not correct. Logically, the first culprit assumed is MAF (air mass meter). Unfortunately, in none of the cases did MAF replacement (installation of MAF from another/working engine or installation of a new OEM sensor) help. Replacement of MAP and the throttle did not help either. EGR data – correct.
The most interesting is that all problems disappear in Stratified charge. Symptoms disappear, and the error messages are not recorded in the DME error message memory (as long as the car runs in this mode).
In all cases, a significantly increased gas flow in the engine crankcase was observed.
To evaluate the airflow in the crankcase:
a. start the engine; do not press the accelerator pedal (it will guarantee that the engine works in Homogenous mode);
b. open the oil filling cap. If you feel a strong airflow vibration, the situation is suspicious, and you have to switch to the next test.
Test No.2:
a. block the CCV air duct to the inlet manifold, placement marked in the image
b. start the engine;
c. open the oil filling cap;
d. you can ask someone to operate the accelerator pedal for a little while.
If you feel a significant, pulsating, directed outwards air flow – there is a problem.
Here is an example – significantly increased gas pressure in the crankcase:
Without any options, some of the gases get into the crankcase. There is only one option for how the gases can get in there – flowing between the piston and the walls of the block. In the correctly performing engine, this gas flow is held by the tiny gap between the piston and the walls of the block, as well as the compression rings. If the gases in a large amount can pass both barriers, there is not only one problem here (in the piston group).
A note is in place here – exactly the N43 series engines have problems with the increased air pressure in the crankcase. For the N53 series engine, the situation is much better. But, till a certain moment, this gas pressure is not creating any problems. It is a normal wear of the engine, which is inevitable.
If you detect such a problem with the gases in the crankcase – unfortunately, a serious repair is needed for the engine. The wear of the parts (block, pistons) should be clarified – if it is over the norm, the part should be replaced; the compression and oil rings have to be replaced, too.
In conclusion, here are some of my observations that can be useful to you.
For the engine, hose one of the cylinders was stubbornly “lazy” in the Homogenous mode, I performed a cylinder switch-off test, ../F9/F2
In this test block, it is possible to switch off cylinders sequentially (attention: cylinders are displayed in the firing order). When the lazy cylinder was switched off, the amount of gases in the crankcase was reduced significantly. With this, I got one more confirmation that exactly this cylinder is the culprit.
Parallel to this test, I decided to perform a compression measure for each of the cylinders. Interestingly, compression was within the allowed limits. Yes, it is possible that for some 0.5 bar lower than for other cylinders, but – in the allowed limits!
Then, I decided to perform the cylinder leakage test. Unlike the compression test (the “most sensitive” stage of which is close to exactly the highest point of the cylinder), the leakage test allows for checking of the gas leakages in other piston positions (both close to the average position and the lowest position, etc.). Unfortunately, the leakage test, too, did not indicate any large losses!
I have several explanations for such result (unsuccessful/negative) of the test:
a. during the test, the pressure is only around 2 bar, but for the working engine – higher several dozen times. A higher pressure may deform the rings (even more – if they have been overheated and become “soft”);
b. the test happens at room temperature, but the gases are several thousand oC hot at the time of combustion. If the piston (or/and the block too) has large wear, the hot gases hit the rings in large volume and overheat/deform them.
My suggestion: don’t rely on compression and leakage tests! The conditions in which these tests are performed are very far from the actual work conditions of the engine. Measurements of cylinder mechanical performance (INPA or ISTA readings) and the evaluation of the amount of gases in the crankcase give more reliable results.
Btw, to evaluate the gas pressure in the crankcase, BMW AG suggests using a special tool IMIB (actually – a regular manometer), to which the pipe A5E0134072 should be attached and the other end of which is screwed on as an oil filler cap and allows the pressure in the crankcase to be assessed. Yes, this test is not correct without a blocked CCV pipe, but – still better than nothing.
