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Knock sensor .The computer adjust ignition timing to be as advanced as possible without resulting in engine knock .First it advances the timing until the engine knocks . Then it retards the timing until the knock goes away . It will then search for the best timing setting for that rpm load temperature and fuel . When it finds the best setting, it stores the information in memory for future drive cycles.Its an adaptive learning to find optimal engine performance.
When the knock sensor detects detonation it will retard the engine timing till engine detonation knock , spark knock , goes away.The relearns the best timing for the fuel by advancing the timing until detonation occurs, then retarding the spark slightly until the detonation stops . . All modern automotive engines have this capabiltiy . Design engineers test an engine on a dynamometer using fuels of different octanes . Different spark advances are tested at various speeds and loads to determine the engines highest torque value.Ignition timing is best when it is advanced to the furthest point without causing detonation . detect bad ignition timing , main bearing knock or piston slap.Detonation can cause the piston to expand too much resulting in cylinder wall scuffing at the four corners of the piston skirts. From the extreme heat the aluminum melts and the piston rings stick to the cylinder wall.
Detonation is a race between the flame front and heat buildup during combustion. The faster the burn is completed , the more immune the engine is to detonation. If the the air fuel mixture burn is completed before the temperture and pressure reach the point of detonation, abnormal combustion will not occur.
Excessive advanced timing can cause ,
excessively retarded ignition timing will cause an engine to overheat but will not burn a piston . Detonantion from overheating , too lean an air fuel mixture air leak into engine cause engine to run lean and overheat . Air fuel mixture to lean .
EGR VALVE FAILING A LEADING SOURCE OF DETONATION testing of egr valve will need to be performed by manually opening valve where knock occurs 1800 to 2000 rpm . If knock goes away egr valve is at fault. To manually open valve .
Older engines, used a air cleaner stuck in the heat on position or a malfunctioning early FUEL EVAP SYSTEM.
A loose sensor bracket or some thing other vibration can also cause the time to be retarded can cause false knock senses. +++++-
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Does anyone have any input on bleeding this vehicle What are the steps on the DELPHI VI How to bleed it ?