VANOS / Variable Valve Timing

🧠 Part of the TuningBot ECU Knowledge Base — in-depth documentation on ECU logic, maps, emissions systems and safe calibration methods.

Variable valve timing (VVT) systems — BMW VANOS, Toyota VVT-i, Honda VTEC — adjust camshaft phasing relative to crankshaft position. This optimizes volumetric efficiency, power output, and emissions across the entire RPM range.

Overview

The ECU continuously adjusts intake and/or exhaust cam timing based on RPM, load, and temperature. Advanced intake timing improves low-RPM torque; retarded timing favors high-RPM power.

Controlled Signals

  • Oil control valve (OCV) duty cycle
  • Camshaft position sensors
  • Oil pressure and temperature
  • Engine RPM and load

Maps Involved

  • Intake Cam Target Maps vs RPM/load
  • Exhaust Cam Target Maps
  • Cam Overlap Maps
  • Cold Start Cam Position Maps
  • OCV PWM Maps

Logic Sequence

RPM & Load → Cam Target Lookup
         ↓
Oil Pressure / Temperature Check
         ↓
OCV PWM Command
         ↓
Cam Position Feedback → Closed-Loop Correction

Calibration Objectives

  • Maximize low-RPM torque
  • Optimize high-RPM breathing
  • Control internal EGR via overlap

Calibration Strategy

  • Advance intake cam for better spool/low-end torque
  • Reduce overlap at idle for stability
  • Coordinate with boost and ignition maps
  • Verify oil system can support aggressive changes

Diagnostics

  • Cam timing correlation faults
  • OCV stuck open/closed
  • Rough idle from excessive overlap

Best Practices

  • Use quality oil and maintain oil level — VVT is oil-dependent
  • Data log actual vs target cam position during testing

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