ECU control strategies are either open-loop (map-based only) or closed-loop (using sensor feedback). Understanding when each is active is crucial for effective calibration.

Visión general

Open-loop control uses pre-programmed maps without sensor feedback — “set and forget.” Closed-loop control continuously adjusts based on sensor readings to maintain a target. Most systems use both modes depending on operating conditions.

Open-Loop Operation

Maps/Tables → Actuator Commands
(No feedback correction)

• Faster response (no feedback delay)
• Requires accurate calibration
• Used when feedback is unavailable or unreliable

Closed-Loop Operation

Target Value → Compare to Sensor
         ↓
Error → PID Controller
         ↓
Correction → Actuator
         ↓
Sensor → (loop back to compare)

• Self-correcting for wear and variation
• Can compensate for altitude, temperature, aging
• Slower response due to feedback delay

Lambda/AFR Control

• Closed-loop — cruise, part throttle, idle (targeting stoichiometric)
• Open-loop — wide-open throttle, cold start, high load
• Transition — ECU switches based on load, temperature, catalyst temp

During open-loop, the ECU relies entirely on fuel maps — errors aren’t corrected.

Boost Control

• Closed-loop — PID control maintains target boost vs actual
• Open-loop — fallback if boost sensor fails
• Feedforward — base duty cycle from maps, PID corrects error

Control de golpes

• Closed-loop — retards timing when knock detected, advances when clear
• Base timing — open-loop starting point from maps
• Learning — long-term adaptation stored in EEPROM

EGR Control

• Closed-loop — using MAF sensor to verify EGR flow
• Open-loop — using position sensor feedback only
• Model-based — calculated flow vs target

When Closed-Loop Disables

• Cold engine — sensors not yet accurate
• Wide-open throttle — response time critical
• Sensor fault — fallback to open-loop
• Regeneration — DPF regen uses open-loop enrichment

Fuel Trims

Fuel trims are closed-loop corrections stored by the ECU:

• Short-term fuel trim (STFT) — immediate corrections
• Long-term fuel trim (LTFT) — learned corrections over time
• Normal range — ±10% indicates proper calibration
• Large trims — indicate air/fuel system issues

Calibration Implications

• Open-loop regions require precise map calibration
• Closed-loop compensates for small errors automatically
• Fuel trims reveal calibration quality in closed-loop regions
• WOT tuning is open-loop — no safety net from sensors

Best Practices

• Verify closed-loop operation with scan tool data
• Monitor fuel trims after tuning changes
• Open-loop WOT requires careful wideband verification
• Understand when the ECU will and won’t self-correct