Valvetronic is, most probably, the most hated hub of the BMW engine. In the same time, it’s “last hope” of the engine repair specialists – if they are not able to find the cause of the problem, most probably, Valvetronic will be the one to blame. Of course, sometimes it can really be damaged, but the understanding about this hub is limited – “that on the top of the engine”, and it’s replaced without reason.
So in this post, I will gather my experience regarding Valvetronic.
What is Valvetronic?
Valvetronic changes (reduces) the opening of inlet valves and allows the inlet valves to perform as an individual throttle of each cylinder.
Why is it Valvetronic necessary, if the engine already has a throttle?
If the amount of air is regulated with inlet valves, not throttle, there is no air shortage in the inlet manifold – the air is not “sucked out”, and pumping losses are avoided. The avoidance of such air pumping gives even till 10 .. 15% fuel economy (larger economy is in low/average load area and idle). The effect is similar to using the principle of Stratified charge in N43/N53 series engines.
How does the performance of the engine differ with and without Valvetronic?
Without Valvetronic – the air supply is managed with throttle opening, inlet valves in all cases are opening with maximum stroke (8 .. 10 mm).
With Valvetronic – the throttle is fully opened, the amount of air is manages with the stroke of inlet valves (0.4 .. 10 mm).
The stroke of the valves is minimal in idle (0.4 .. 0.8 mm) and maximal – pressing the accelerator pedal to the end.
In the picture – construction of Valvetronic. More detailed information, how does the Valvetronic works, you can find in the aftersales materials of BMW AG, in this entry I will pay more attention, how to detect defects of Valvetronic.
Some notes regarding construction:
a) motor (1) is a regular DC motor, connected with 2 pin connection. DME controls the voltage, supplied to the motor (the Bridge type controller is used to manage the voltage – the voltage can change the polarity) and current, consumed by it;
b) position of the eccentric shaft is controlled by very accurate Holl sensor module, which is placed at the end of the shaft, near the first cylinder.
The first group of defects: faults, detected by DME.
DME controls performance of two hubs:
a) motor. DME contains the map with information about the allowed consumption of the current, depending on the voltage, supplied to it. Even more – DME collects the information regarding this coherence (I/U) for the current motor.
Accordingly – DME will record the error message regarding absolute value (power/current consumption too high or too low), also the error messages regarding correlation/plausibility, if under the same conditions the current, consumed by the motor, will be significantly different;
b) module of sensors. DME continuously controls signals of Valvetronic sensors and immediately records the error messages regarding their performance, if signals of sensors are incorrect. DME creates the adaptation map of the eccentric shaft – it compares data of the sensors with air, consumed by the engine, in current mode. The adaptation map allows quickly and accurately place the eccentric shaft in the necessary position (already foreseeing exact position – compensating technological allowances of the sensor itself and also the shaft).
Based on data of both hubs, mentioned before, DME calculates time, which is necessary for the engine to turn the eccentric shaft till exact position and corrects voltage, supplied, to the motor (creates adaptation map) in such way, that this turning is performed with most optimal (required) speed.
c) the error messages regarding mechanical issues – are recorded if in the estimated time (including a certain reserve) the required position of the eccentric shaft is not achieved (or is not achieved at all).
If the error message regarding Valvetronic is recorded, it is very significant not only to read the error message code but also collect all information regarding obstacles, when the error message was recorded. For this cause use the INPA freeze-frame.
For example, the error message regarding the inadequacy of current consumption can be caused by a problem with the motor itself or also periodical pledging of the eccentric shaft. If, for example, it’s registered, that for some moment the current was to low (0.0A) – definitely the motor or its connection (wires, connector) is defective (most probable cause – the contact of its brushes is lost), but, if the consumption of the current has been increased (for example, 25.0/30.0A) – the motor was, obviously, is mechanically braked or damaged.
Note: when the engine is cold, for first 60 seconds Valvetronic is switched off (it’s also switched off till next session in cases, if DME has detected a problem with its performance) – the eccentric shaft is moved in such way, that the valves can make max “walk”, the air supply is regulated with throttle – as for “old type” engines.
A situation, when the appropriate error message regarding the performance of the Valvetronic is recorded, is comparatively simple. The motor (most often), sensor module (very rare, but it’s also a quite expensive hub) – there are not many parts, which are often damaged. In cases, when there are no error messages regarding Valvetronic, but the performance of the engine is “abnormal”, it’s much more complicated.
Problems with Valvetronic, but no errors (relating to Valvetronic) stored.
Valvetronic has it’s “Achilles heel” – weak spot. These are technological tolerances and exceeding on them due to wear of the spare parts. This problem is more actual in idle and low load conditions. As already mentioned before, in idle the valves are opening for (average) only 0.4 .. 0.5 mm (min opening allowed is 0.18 mm)! If by opening 0.4 mm mechanism of any valve “makes mistake” for only 0.2 mm (it’s not much, as we know), the valve will open for 2 (!!!) times less than needed! Accordingly – the cylinder will receive for 25% less air as required (in situation, if another inlet valve performs correctly), the fuel mixture will be very rich, mechanical efficiency – significantly decreased (because 25% of fuel will not be burned), load for CO catalytic converters will be very high (because the unburned fuel will get in the CO catalytic converters), the engine will shiver, DME will not be able to fix the situation. The same situation will be reached if both inlet valves are moved only 100 microns (0.1mm) less than necessary!
Moreover, high precision of details has to be compiled for almost all Valvetronic components (in the picture: positions No.4, 6, 12 and 14) and HVA (No.7).
But I must add right away – unfortunately, opposite to good thing, which is Valvetronic doing (it saves fuel), it worsens the balance of cylinders (proportion of fuel mixture and mechanical efficiency) in idle and in the low load area. It is understandable, that each mechanical hub has it’s manufacturing precision, wear. Unfortunately, the existing generation of Valvetronic has no tools, which would allow changing (correct/equalize) movement of valves of each cylinder, if necessary.
How does DME even the performance of cylinders in idle? For cylinders, which efficiency is higher than average – it decreases fuel amount and let’s work with (a bit) lean mixture. Cylinders, which inlet valves are performing slightly decreased movement (they have air shortage), has to work with the slightly enriched mixture, for an average fuel mixture of all bank (or all cylinders) would be correct (with Lambda 1.0 or other value, required by DME). As a result, the mechanical efficiency of cylinders is evened, but chemical disbalance is solved by CO catalytic converters burning the excess fuel. Of course, this solution has its limitations. For example, if one cylinder will receive only 75% or necessary amount of air (previously mentioned difference of 0.2 mm for one valve), other cylinders will have to work with the lean fuel mixture. As a result – detonation, increased fuel consumption, damaged CO catalytic converters.
Observing performance of several engine management (both Siemens and Bosch), I have to come to conclusion, that:
a) both of them have very similar algorithms to even the idle (no revolutionary changes);
b) range of fuel mixture corrections is limited; if the mechanical efficiency don’t reach required, when limitation of correction amount is reached, applied correction stays in its min/max point;
c) if correction of any (some) cylinder has reached this min/max point, but the performance of cylinder has not even, no error messages are recorded in DME error message memory*, no status bits are available, the amount of applied corrections is not easily to review (yes, INPA offers ../F9/Shift+F2 data for MSV70/80, but for a “normal person” the interpretation of such data could be quite complicated, algorithms of displayed registers are not known; but for ME/MEV engines even this information is not available).
As we know, repair specialists of dealer centers have only ISTA D available (INPA is not allowed for use), and it displays only Rough run data (and also without any explanation and status bits – for example, is/not the idle evened, is/not the min/max range reached, does the positive value means increased or decreased efficiency, is it mechanical or chemical efficiency etc).
* this is the difference of engines with Valvetronic with, for example, N43/N53 engines – as soon as the exact “corridor” of correction is exceeded, DME MSD80 records the error message ”cylinder X, trim control over limits” and switches off the engine to even the performance of cylinders.
Observing the performance of software, I have concluded:
ISTA D: Rough run data are displaying mechanical efficiency, the sequence of cylinders: placement; increased value – decreased efficiency, status bits: none.
INPA (MSV70; loader 1.35) displays mechanical efficiency, sequence if cylinders: placement; increased value: decreased efficiency, status bits: none.
INPA (MSV80; loader 1.007) – sequence of cylinders: incorrect/wrong.
INPA (ME9.2/MEV9; loader 2.04) displays mechanical efficiency, the sequence of cylinders: placement; increased value: decreased efficiency, status bits: none.
INPA (MSD80, loader 2.023) displays mechanical efficiency, the sequence of cylinders: firing order; increased value: decreased efficiency, status bits: none.
Suggestion: if you are using INPA (to view Rough run data you can use the loader for related engines), check the sequence of cylinders! How to do that? For example – disconnect the ignition coil of cylinder No.2 for a moment. Rough run data will display the sequence of cylinders, displayed on the screen. If you will interpret the sequence of cylinders wrongly, you will make wrong conclusions!
To “ease” the situation, even more, these engines mostly (both – MSV: N52, and ME/MEV: N42/46) don’t report misfire counters via OBD mode 6, which means – diagnostic of ignition problems is quite complicated.
Note: misfire data is available for N54 (MSD80) and N55 (MEVD17.2) series engines.
At this moment we have reached the sentence of this entry: how to detect if the Valvetronic is the cause of incorrect performance?
If the cold engine worked incorrectly directly after starting, the most common problem of Valvetronic – technological allowances/wear are not the cause (because the Valvetronic is turned off). Of course, with the condition – it’s functionality is not disturbed (there are no problems with motor’s performance – it is able to move the eccentric shaft to the position of max opening).
Also then, if the significant disbalance of cylinders will appear in high load – technological allowance of Valvetronic will not be the right cause!
Typical situation (where the technological allowances of Valvetronic can be the cause) – permanent vibration in idle, in worst cases – possible misfires.
What to do?
At first – prepare for the work. Open the profile of the corresponding engine (if we use INPA), make sure, that:
a) other problems are solved – there are no error messages regarding basic systems of the engine;
b) the engine heats up to the working temperature (the thermostat is OK, no Mapped/emergency mode is switched on);
c) all Lambda probes are heated, signals of wide-band probes are correct (the engine is able to maintain the Stoichiometric mixture); control probes are able to generate required voltage (their readings can periodically drop down to 0.0 .. 0.1 V if the misfires can be sensed);
d) open Rough run data, check the sequence, how the cylinders are displayed.
If permanent vibration can be felt, Rough run data are supposed to display permanent disbalance.
Keep this menu open, switch off/on the engine repeatedly. If the engine smoothes out the idle (works in full functionality mode), directly after starting the engine, the disbalance, displayed by Rough run data, should be increased, during several tenths of seconds situation has to improve (disbalance has to decrease). If it’s not happening (or situation is getting even worse), obviously – the engine doesn’t equalize the mechanical efficiency of cylinders.
This situation can have following causes:
a) there are error messages regarding some other system of the engine – they have to be solved;
b) there are no error messages. Obviously, after repairs (and deleting of the error messages), performed before, re-adaptation of the engine is not performed. Solution: re-adapt the engine.
Re-adaptation of the engine (it’s initiation).
ME/MEV systems. Delete all adaptations (status: ignition – on; engine – off) in the corresponding menu; turn on the engine, wait, till wide-band Lambda probes are starting to work (their voltage readings are becoming different for 1.50 V).
MSV systems. Delete all adaptations in the corresponding menu (status: ignition – on; engine – off); perform the adaptations of the flywheel; turn off engine, wait till MSV goes to ‘sleep’/turn on the engine, wait, till heating of wide-band probes starts (their PWM increases above 10%).
If the situation, when the engine evens the idle, is achieved, but Rough run data still are displaying that the balance is not reached (in case of balance – Rough run bar of each cylinder is close to 0.00), we can assume, that the correction of some cylinder has reached min/max range.
In this situation – switch off the Valvetronic and check, is the problem actual also then:
a) memorize approximate Rough run data (cylinder(s), which mechanical efficiency in decreased);
b) switch off the engine;
c) disconnect the Valvetronic sensor – the engine will switch to emergency mode (without using Valvetronic);
d) switch on the engine;
e) evaluate the Rough run data.
If the problem has disappeared – Rough run data shows even performance of cylinders, we can assume, that the problem exists in the mode when the valves have a small opening (attention – this IS NOT a confirmation, that the Valvetronic is the cause of the problem, description will follow);
if the problem is still present, obviously, the Valvetronic IS NOT the cause of the problem. In this situation:
a) measure the compression (evaluate the valve closure, amount of burn etc.);
b) check the injectors.
If the problem is not present, when the Valvetronic is switched off, continue the search of the problem. For this reason:
a) take off the valve cover;
b) turn off the fuel pump;
c) unscrew the Valvetronic motor and disconnect from DME;
d) move the eccentric shaft to the position, where the opening of inlet valves is 0.
In the image, marked with red:
the Valvetronic motor is not screwed to the end – changing its hulls distance to the bracket (slowly screwing it), the position of the eccentric shaft is adjusted;
with the screwdriver, the movement of the inlet valve of the 2nd cylinder is controlled.
Detecting the localization of the defect:
a) press the inlet valves of “good” and damaged cylinder one by one, to feel their movement;
b) ask the assistant to start the engine for some seconds in the necessary moment;
c) repeat a and b activities, slowly turning the eccentric shaft, till valves of any “good” cylinder start to open.
To turn and fix the eccentric shaft, it’s convenient to use the Valvetronic motor (it has to be disconnected), slowly screwing it in the anchorage or turning its axle.
This method allows finding a valve(s), which openings are significantly different (typically – the valve openings will be smaller for the cylinder, which mechanical efficiency is decreased) from conditions of small opening of valves (idle). When the different valve(s) is (are) found, we have to clarify the cause of the problem more precisely.
The cause of these differences cannot only be of Valvetronic hub but also valve adjuster(s) (HVA, position No.7 in the image above).
When the valve(s), which is not opening, is detected (in circumstances, when the valves of “good” cylinders are already opening):
for the valve, which is not opening – check with the screwdriver, if the corresponding Intermediate lever (position No.13 in the picture) performs the movement downwards – pressing the screwdriver to middle point of Roller cam follower (position No.12 in the picture), or, if possible, to HVA (position No.7 in the picture).
If the Intermediate lever performs the downwards movement – moves Roller cam follower, when the engine is started, obviously, the HVA of the inlet valve is defective – it has increased detail “play” or HVA is not working properly because of reduced oil pressure.
If the Intermediate lever doesn’t perform the movement downwards (Roller cam follower don’t move), when the engine is started, obviously, it’s wear is increased, or the wear of the eccentric shaft is increased.
In the picture:
A: control spot of the valve lift;
B: control spot of the vertical movement of the Intermediate lever;
C: control spot of HVA “play”.
Although this method don’t allows to detect the exact damaged element (if some exact component of the Valvetronic valve management has worn out – to identify it, you have to use the micrometer and compare the details one with other, evaluate the “play” between moving element; if the HVA has increased “play”, make sure, that the oil channels are not clogged), it allows to localize exact inlet valves, detect the approximate location of the problem and avoid the method “let’s change all HVA and all details of Valvetronic – it should help”.
N46 series engine, with increased vibration in idle.
The engine reached work temperature, wide-band probe shows Stoichiometric mixture (voltage: around 1.50 V), control probe is able to generate the voltage till 1.00V; adaptive correction – small, integrator – performs it’s duty (in range of +/-5%).
Viewing data with INPA (ISTA confirms Rough run data – data are correct): Rough run data showed: around -1.3 .. -1.8 units for cylinders 1, 2 and 3, and +3.0 .. 4.0 units for cylinder No.4.
Conclusion – the cylinder No.4 has significantly decreased mechanical efficiency, other cylinders are displaying similar efficiency – their performance is correct. Directly after turning on the engine, disbalance is even higher, cylinder No.4 reaches around +6.0 units and during 5 .. 10 seconds decreases to +3.0 .. 4.0 (it means, the engine tries to equalize the idle by its possibilities).
Turning off the Valvetronic, the performance of the engine normalizes, Rough run data of cylinders was in range -0.2 .. +0.3 units, obviously – the defect is characteristic exactly for a current mode when the inlet valves are performing small moves.
Testing the openings of the valves mechanically was detected, that the 1st inlet valve of cylinder No.4 doesn’t open in the situation when both valves of cylinder No.1 have significant movement. Conclusion – the damage is localized to the 1st inlet valve of the cylinder No.4. Special attention has to be paid to the HVA.