Knock retard and timing pull under load

Ignition advance drops away under load and power softens, sometimes varying tank to tank or with ambient heat. Logs show knock retard (knock correction) being pulled, steadily or in spikes, and timing not returning to the commanded value.

Knock control listens to the knock sensors and, when it detects what it reads as detonation, retards ignition timing to protect the engine. Pulled timing under load therefore has two possible roots. The first is genuine knock: too much advance for the fuel octane, high intake air temperatures, a lean mixture, carbon hot-spots, or simply more cylinder pressure than the fuel can tolerate. The second is a false read: mechanical noise (injectors, valvetrain, a loose accessory) sitting in the knock sensor's frequency window, which the system mistakes for detonation and reacts to anyway.

Calibrating the timing without first telling these apart either leaves the engine exposed or throws away safe power.

Separate real knock from a false read first. Real knock tracks with octane, intake air temperature, load and AFR; a false read tends to be RPM- or noise-linked and consistent regardless of fuel or heat. The fuel actually in the tank (98 RON, an E85 blend, and so on) has to match what the calibration assumes.

If it is real, bring the base ignition timing back to what the fuel and conditions support, address the contributors (mixture under load, intake air temperature management), and leave the knock system its margin as a safety net — not as a substitute for a correct base map. If it is a false read, the knock-detection windowing/sensitivity is the area to review so the system stops reacting to mechanical noise.

Verify against logged commanded vs actual ignition timing, knock retard/correction per cylinder, intake air temperature, AFR/lambda and fuel type. A good result holds the commanded timing under load with the knock system quiet, repeatably and across heat.