The rev limiter is a critical engine protection function that prevents over-revving by cutting fuel injection or ignition above a threshold RPM. This protects the valvetrain, pistons, connecting rods, and bearings from catastrophic damage.

Vue d'ensemble

Modern ECUs use “soft” rev limiters that progressively reduce torque before a “hard” cut. This provides smoother behavior and reduces drivetrain shock.

Controlled Signals

• Engine RPM (crankshaft sensor)
• Fuel injection enable/disable
• Ignition enable/disable
• Torque request limiting

Maps Involved

• Soft Rev Limit Threshold
• Hard Rev Limit Threshold
• Torque Reduction Rate
• Temperature-based Rev Limits
• Oil Pressure-based Limits (some vehicles)

Logic Sequence

Engine RPM → Compare to Soft Limit
         ↓
If above soft limit → Reduce torque progressively
         ↓
If at hard limit → Fuel/ignition cut
         ↓
Resume when RPM drops below threshold

Calibration Objectives

• Protect engine from mechanical damage
• Allow maximum usable RPM range
• Smooth transition at limiter

Calibration Strategy

• Raise rev limit only if engine internals support it
• Verify oil supply at higher RPM
• Check valve float threshold

Diagnostics

• Crankshaft sensor faults affect rev limiting
• Unexpected rev limiting may indicate other issues

Best Practices

• Stock internals = stock rev limit (with small margin)
• Upgraded valvetrain allows higher limits
• Always verify oil pressure at new redline