Which cylinders does the Honda VCM deactivate?
Honda's Variable Cylinder Management (VCM) deactivates two cylinders at certain speeds and loads, one from each cylinder bank, so the engine can run on four cylinders under light use to save fuel. The exact cylinders deactivated are not fixed across all models; the engine management system selects the pair to minimize vibration and maintain smooth operation.
How VCM Operates in Real-World Driving
When cruising under light load, the VCM can switch the V6 into a four-cylinder mode by deactivating two cylinders. The transition is controlled by the engine’s electronic control unit, and the system reactivates all six cylinders as soon as more power or higher load is required. This process aims to be seamless from the driver’s perspective, with no noticeable interruption in acceleration or throttle response.
Before outlining the practical details, here are the core points about which cylinders are affected by VCM:
- Two cylinders are deactivated at a time, one from each cylinder bank, to create four-cylinder operation during light-load conditions.
- The exact cylinders shut off are dynamically chosen by the ECU based on engine load, RPM, temperature, and other factors to minimize vibrations and preserve smoothness.
- All six cylinders are re-engaged when more power is needed or when conditions no longer favor cylinder deactivation.
- Different Honda models and engine variants implement VCM with some variation in thresholds and cylinder-pair selections, so there isn’t a universal fixed pair for every vehicle equipped with VCM.
Concluding: The VCM system is designed to balance fuel economy with drivability, using adaptive cylinder deactivation (two cylinders at a time, one from each bank) that varies by model year and engine variant.
Notes on Model Coverage and Practical Experience
VCM applications span several Honda and Acura models with the 3.5L V6 and related engines, including generations of the Accord, Pilot, MDX, Odyssey, and others. For owners or buyers, it’s useful to review the specific vehicle’s owner’s manual or official service bulletins for precise behavior and any model-year nuances, as thresholds and cylinder-pair selections can differ slightly between variants.
Summary
In short, Honda VCM deactivates two cylinders at a time—one from each bank—to operate the engine as a four-cylinder under light-load conditions. The exact cylinders deactivated are determined by the engine control system and can vary by model year and engine variant. When more power is required, the system reactivates all six cylinders to restore full performance.
Does the Honda V-6 have cylinder deactivation?
When maximum power isn't needed, the VCM system can deactivate one bank of cylinders—depending upon the torque requirements to maintain cruising speed—by shutting off the appropriate fuel injectors and stopping valve operation with the VTEC® system.
Can a VCM tuner cause any long-term damage?
However, VCM also reportedly causes problems, like engine shuttering and vibration, fouled piston rings, carbon buildup, fouled spark plugs, excessive oil consumption, rough idling, and misfires.
Does cylinder deactivation damage the engine?
Yes, cylinder deactivation can cause engine problems, mainly related to increased wear on specific components like the hydraulic lifters and solenoids, which can lead to a "ticking" sound and eventual failure. Other issues can include unbalanced vibrations, injector imbalance, and potential issues with the turbocharger or exhaust system due to pressure pulses and temperature changes. Early models were more prone to problems, but modern designs are better, though the added complexity still introduces potential failure points.
Potential problems with cylinder deactivation
- Increased wear on lifters and solenoids: The lifters in deactivated cylinders can wear out prematurely because they are being rapidly engaged and disengaged. The solenoids that control oil flow to the lifters can also fail over time.
- Vibrations: When a cylinder is deactivated, a 4-cylinder engine running on 3 cylinders experiences unbalanced forces, leading to increased vibrations that can be felt in the cabin and potentially cause premature wear on engine mounts.
- Oil consumption: A lack of lubrication due to worn-out piston rings in the deactivated cylinders can lead to increased oil consumption and a lack of lubrication.
- Injector and exhaust system issues: Deactivating a cylinder can cause pressure pulses in the common rail, which is harmful to the injectors. It can also create issues with the turbocharger and exhaust manifold due to changes in exhaust gas pulses and temperature.
- Software and mechanical failures: Errors in the software controlling the system can cause a misalignment of the intake valve rocker arm, leading to misfires or loss of power. The added complexity of the system can lead to premature failure of some components compared to a simpler engine.
- Maintenance requirements: Vehicles with cylinder deactivation systems require the correct, full-synthetic oil to function properly. Using the wrong viscosity or type of oil can prevent the system from working correctly.
Modern vs. older systems
- Older systems: Early cylinder deactivation engines suffered more significant problems with wear and tear over time.
- Modern systems: Newer engines have improved designs that have reduced many of these issues, but the added complexity still introduces potential points of failure.
Conclusion
While modern cylinder deactivation systems are more reliable, they introduce additional complexity and potential failure points compared to non-deactivation engines. The main issues revolve around the increased wear on the valvetrain components, potential for vibrations, and the risk of failure in either the mechanical components or the control software.
Which cylinders does the Honda VCM disable?
3 cylinders
In many cases, when VCM shuts down 3 cylinders, it only shuts down 1-3. 5 and 6 are completely non-VCM. More likely you have a misfire for other reasons. The timing belt being off even one tooth is a common cause for this.
