This can cause a rattling noise at startup and idle. When this happens, the gear can’t fight the pressure exerted on the camshaft by the valve springs. This causes the actuator to be stuck or hydraulically jammed in either the full advance or retard positions. The most common failure is when the O-ring seal on the piston wears out and allows oil pressure to move between the two chambers. This can cause noise and rattle at idle and startup. The helical gears on the actuator and camshaft can wear. The two most common failures for a VANOS system are related to the quality of the oil. But, like helical-gear actuators, they still require a quality supply of oil to operate. The same diagnostic basics apply to these systems. Later engines, like the N54 inline-six, have more common actuators with the chambers inside camshaft sprockets. A code will be set if the actuator and camshaft do not return to the correct position, because they are hydraulically jammed due to oil pressure leaking past a seal. If the oil pressure can’t move the camshafts to the target positions in a specified time, the camshaft position sensors will sense it and set a code. If the oil is contaminated or is the wrong viscosity, the VANOS system can become sluggish. The solenoid is actuated by a pulse-width modulated signal. The more common design is a spool valve to control the oil on either side of the piston. For some S54 engines, they use a module with valves that resemble those found in an ABS modulator. A solenoid controls oil pressure on either side of the plate to control the depth of the gear.īMW has used two solenoid designs for dual-VANOS units. Connected to the gear on the actuator is a plate or piston with oil pressure on both sides. ![]() The timing is changed by moving the depth of the helical gear on the actuator, inside the gear on the camshaft. Most VANOS systems use a gear on the actuator and a gear on the camshaft that have angled or helical-cut teeth. The actuators need a consistent supply of oil for the correct viscosity, pressure and volume. Like many variable valve timing systems, VANOS uses oil pressure-powered actuators to move the camshafts. These symptoms are common to any other variable valve timing system. When the VANOS system is not working, the most common symptoms are poor idle quality, reduced power and poor fuel economy. ![]() Also, the camshaft position is changed to reduce engine warm-up times by allowing some unburned fuel to reach the catalytic converters. The system can augment and even eliminate the EGR valve by allowing some of the exhaust gas to remain in the combustion chamber to control combustion temperatures and NOX emissions. At higher engine speeds, the valves open later for full power delivery so the scavenging effect of the exhaust leaving the cylinder can pull more air into the cylinder. As the engine rpm increases, the valves are opened earlier. This improves idle quality and smooth power tip-in from a stop. This increases the vacuum and scavenging effect generated by the piston traveling downward in the cylinder. Later dual-VANOS systems operate at all engine speeds.Īt lower engine speeds, the VANOS system opens the valves later during the intake stroke. The early VANOS systems are very basic and work to make more power. This system also changes how the engine is throttled, which we’ll discuss later in this article. Later systems, known as Valvetronic, take VANOS to the next level by adjusting the lift of the valves. Some newer systems can change the camshaft timing by as much as ☗2 degrees. ![]() These systems adjust both the intake and exhaust camshafts. The first dual or bi-VANOS system was then introduced on the 1996 M3. These early VANOS systems could change the camshaft timing by 12.5 degrees for better performance. VANOS systems have evolved over the past 25 years, from the first single-VANOS systems that were on the intake camshaft of the 1993-1998 engines found in 325i and 525i models. You will also need a scan tool and a scope to observe the crankshaft and camshaft signals to accomplish more advanced diagnostics. As for tools, you will need the appropriate tool set to lock the crank and camshaft. What it does demand, however, is knowledge of how the actuator adjusts the camshaft, how the solenoid controls the actuator and when the engine control module changes camshaft timing. ![]() The key word to remember for a late-model VANOS system is that it works “continuously” and not just under specific rpm ranges.ĭiagnosing a VANOS system does not require that you speak German. The latest versions continuously adjust the position of the intake and exhaust camshafts for better power, efficiency and idle performance.
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