BMW's Innovative Throttle System is referred to as valvetronic.

The workings of a mechanical system BMW had developed to alter the lift of the intake valves on equipped engines were discussed in a previous article.In this article, we will discuss some of the issues that affect Valvetronic systems, as well as provide some diagnostic and servicing tips.Let us start.

The first iteration of the Valvetronic system was introduced in 2002.The third iteration of Valvetronic systems is used on almost all BMW engines across the range of BMW vehicles.

The Valvetronic system on any given BMW model is said to produce an effect known as "throttle-free" load control.The BMW literature refers to this as an engine control mode that is different from a control Mode in which the throttle opening controls the engine load.The best thing to do is to remember that when a BMW engine is running, the throttle opening is held to an opening of between 3% and 4% by the DME, while the amount of commanded intake valve lift controls the volume of air that enters the cylinders.

The intake valve lift can be adjusted to maintain and improve idling speed and quality.The concept of engine control through valve lift, as opposed to controlling the engine through making changes to the throttle opening, is shown by the fact that some adjustment is possible during idling.It is questionable whether or not this is true engine control, but that is beside the point.

The point is that under some operating conditions, the amount of valve lift can control how much air enters the cylinders.

We've all used intake manifolds as diagnostic aids, but they're not the same on BME engines.The low rate of air flow during idling causes the intake manifold vacuum to be low, even though a BMW engine can run when the pressure is equal to atmospheric pressure.

The intake manifold vacuum is programmed to be equal to 1.5 inches of Mercury when the engine is not running.The vacuum is determined by the percentage of throttle opening that is maintained during idling.The degree of throttle opening is almost invisible, so don't condemn the throttle body as the cause of the rough idling problem.

The best place to diagnose idling issues is the differential pressure sensor.The actual vacuum inside the intake Manifold is recorded by the sensor as opposed to the absolute pressure.As an additional check, bear in mind that a high-end scanning tool should display an intake manifold vacuum value of between 0 and 1 millibar, as opposed to between 980 and 1000, which indicates atmospheric pressure.

If the engine has forced-induction, the manifold pressure/vacuum sensor acts as a MAP sensor, which means you should see a manifolds pressure of around 1000 millibar.

The difference in the manifold vacuum readings between naturally aspirated engines and forced induction engines will tell you what type of pressure sensor you are dealing with.If the engine is running in valve lift control mode, this will tell you.

Knowing the difference between control modes is important for the VANOS system.The VANOS fault will cause the engine to go back to full throttle control mode and the eccentric shaft to the almost maximum valve lift position.The manifolds on all Valvetronic-equipped engines will typically be between 600 and 690 millibars.

The engine is running in valve lift control mode if the idle quality is poor but the Scan tool shows an eccentric shaft position of less than 30 degrees of rotation.The Valvetronic system is unlikely to be involved in the poor idling problem.

We hope that the above section has given you a better understanding of how to use vacuum readings to diagnose Valvetronic issues.

The image is from the Search Auto Parts website.

The valve lift curves of two intake valves are shown in the above graph.The red and blue curves describe the valve lift curve on the non-adjustable valve.

The purpose of making only one intake valve per cylinder is to improve combustion as a result of increased turbulence in the intake charge.If the system works as designed, it will produce measurable reductions in both fuel consumption and exhaust emissions, while improving engine power at low to intermediate engine speeds.

While there are slight differences in the valve lift curves for different engines, this example is representative of what the intake valve phasing of a Valvetronic-equipped engine should look like.The horizontal axis represents power output as a function of engine speed, while the vertical axis is for intake valve lift.

In this case, the eccentric shaft is at its maximum position to allow the full cam profile to act on the valve.The lift of the valve is the same as the non-adjustable valve.

The point labelled "6" indicates the point at which the valve lift is limited to 0.2mm until the engine reaches 25% of its rated output.The valve lift increases rapidly after this point.The rate at which valve lift is increased is determined by the input data from various sensors.

The rise in the red curve is between 50% and 60% of the rated power output.The sharp rise is a function of the VANOS system since the non-adjustable valve is not affected by the Valvetronic system.The rise in the red curve is a function of the non-adjustable valve's timing, as opposed to its lift and duration.

Why is this important?It is important because when the Valvetronic and VANOS systems work together as designed, the results are, a), an idling quality that is unparalleled by almost any other vehicle make or engine, and b), a smooth, seamless increase in engine power throughout the engine's operating range.

The points of contact between the eccentric shaft and intermediate arms were usually made with contact pads, rather than the rollers that are found in second-, and third- generation Valvetronic systems.The intake valves opened by equal amounts when the contact pads wore out in poorly maintained engines.This caused poor idling, hard starting, and in some cases, severe misfires at low to intermediate engine speeds and/or loads.

It was possible to increase the minimum valve lift on first-generation Valvetronic systems with a Scan tool.The purpose of the test was to eliminate the effects of mechanical wear on Valvetronic components.If the valve lift increased, the problem could be related to excessive mechanical wear of some components.When the valve lift increased, the problem usually involved issues in the ignition and/or fuel delivery systems.

The introduction of rollers to replace contact pads in second-, and third- generation Valvetronic systems has eliminated rough idling issues because of excessive mechanical wear.Poor idling, hard starting, excessive fuel consumption, misfires, and other driveability issues are usually caused by- since the DME needs to know the position of the eccentric shaft at all times when the engine is running.

The image is from the Search Auto Parts website.

Since the DME has to know the exact position of the eccentric shaft at all times to exert precise control over the intake valve lift, the system uses a complex position sensing system that consists of two separate sensors that are incorporated into a single assembly.

It is usually possible to scope the operation of normal position sensors, but it is not possible with Valvetronic position sensor.The sensors are complicated and do not work with advanced laboratory-grade oscilloscopes.One sensor in the assembly monitors the position of a magnetic ring that was inserted into the eccentric shaft.

The image is from the Search Auto Parts website.

One sensor is known as the measuring sensor because it measures the actual position of the eccentric shaft relative to a known reference point, while the other is called the "evaluation" sensor, which is used as a double check.

During valve lift adjustments, the measuring sensor is monitored continuously by the DME, while the evaluation sensor data is only checked and compared to the data from the measurement sensor.The amount of rotation of the eccentric shaft is correlated with input data from both sensors.The position of the eccentric shaft in degrees of rotation is the only thing that can be checked with a scanning tool.

The best course of action is to replace the eccentric shaft position sensor if there are fault codes that relate to eccentric shafts range and/or performance issues.The position sensor is the most common cause of Valvetronic issues on first- and second- generation systems.

Third-generation Valvetronic systems use position sensors that are integrated into the eccentric shaft actuator motors, so they can't be replaced on their own.

There is one more possible cause of rough running and/or poor idling quality that we need to discuss, knowing that Valvetronic position sensors cannot be scoped.