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In spark-ignition internal combustion engines, knocking (also knock, detonation, spark knock, pinging or pinking) occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.
It's commonly known as "Detonation or Knock". Engine management systems can overcome pre ignition by the means of a knock or detonation sensor. The sensor will detect pre ignition and retard the engines timing to protect the engine from damage. Undesired engine behavior will occur such as loss of performance or power.
The reduced engine speeds allow more time for autoignition chemistry to complete thus promoting the possibility of pre-ignition and so called "mega-knock". Under these circumstances, there is still significant debate as to the sources of the pre-ignition event. [3] Pre-ignition and engine knock both sharply increase combustion chamber temperatures.
Pressure in cylinder pattern in dependence on ignition timing: (a) - misfire, (b) too soon, (c) optimal, (d) too late. In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke.
A bad crank position sensor can worsen the way the engine idles, or the acceleration behaviour. If the engine is revved up with a bad or faulty sensor, it may cause misfiring, motor vibration or backfires. Acceleration might be hesitant, and abnormal shaking during engine idle might occur. In the worst case, the car may not start.
In theory, the closing of all rear bank valves produces an ‘air spring’ effect. However, the reciprocating effect of the piston with closed valves reportedly produces a vacuum condition where oil can get pulled past the piston rings to flood the cylinder. When VCM disengages, the engine then misfires if needing to clear the cylinder of oil.
The double exhaust pulse would cause part of the next exhaust pulse in that bank to not exit that cylinder completely and cause either a detonation (because of a lean air-fuel ratio (AFR)), or a misfire due to a rich AFR, depending on how much of the double pulse was left and what the mixture of that pulse was. [5]
When an internal combustion engine is under high load (e.g. wide open throttle), the output of the oxygen sensor is ignored, and the ECU automatically enriches the mixture to protect the engine, as misfires under load are much more likely to cause damage. This is referred to as an engine running in "open-loop mode".