overboost

Overboost refers to a condition in forced-induction engines where boost pressure temporarily exceeds the intended maximum boost. It most commonly occurs in turbocharged engines, but can also occur in supercharged configurations. The term can describe a brief spike above target (a boost spike) or a longer duration when the boost control system fails to trim pressure.

Causes include boost control malfunctions (wastegate sticking or faulty boost controller), sensor errors (MAP/boost sensor fault), vacuum leaks, intercooler or piping leaks, or rapid throttle movements and gear changes. Ambient conditions such as high altitude or high intake air temperature can also influence.

Effects of overboost can include increased cylinder pressure and temperatures, raising the risk of knock, pre-ignition, and engine damage. Turbocharger stress, higher oil temperature, and degraded fuel economy can also occur. Many modern engines implement safeguards to prevent sustained overboost.

Safeguards and responses involve engine control units monitoring boost levels and taking action such as opening the wastegate more aggressively, retarding ignition timing, or reducing fueling when overboost is detected. Some vehicles may enter a limp mode or illuminate a fault code to prevent damage.

Diagnostics typically rely on symptoms such as unexpected surge-like boost readings, fluctuating power, or a sudden flaring of boost. Investigations inspect the wastegate and actuator, boost pipes, intercooler, hoses, and sensors. Data logging with a scan tool comparing commanded versus actual boost helps identify faults.

In tuning contexts, brief overboost may be deliberately enabled in some maps, but it is restricted by safety limits and legal restrictions in many jurisdictions.