Detonation/Spark Knock
Checks 
 | Action 
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DEFINITION: A mild to severe ping,
usually worse under acceleration. The engine makes    sharp metallic knocks
   that change with throttle opening. 
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Preliminary Checks 
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|     •  | Road test the vehicle and determine the severity of the complaint. |  
  
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Cooling System Checks 
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|     •  | Check for any obvious overheating problems. Refer to 
Engine Overheating 
 in Engine Cooling. |  
  
|     •  | Check for a low engine coolant level. Refer to 
Loss of Coolant 
in Engine Cooling. |  
  
|     •  | Check for a loose water pump belt. |  
  
|     •  | Check for restricted air flow through the radiator, or a restricted  coolant flow. |  
  
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Sensor Check 
 | Check for an engine coolant temperature (ECT)
sensor that has a shifted value.      Refer to 
Temperature Versus Resistance 
. 
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Fuel System Checks 
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|     •  | Check to determine if a lean system causes the condition. Drive  the vehicle at the speed of the complaint. Monitoring the Fuel Trim will help          identify the problem. If the system is lean, the Long Term Fuel Trim     will      be more than 20 percent. |  
  
|     •  | Check for inferior quality fuel and the proper octane rating.  Refer to 
Fuel System Specifications 
.     Fill the fuel tank  with a known high quality fuel that meets the   vehicles     minimum octane requirements.  Road test the vehicle and re-evaluate the     vehicle  performance. |  
  
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Ignition System Checks 
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|     •  | Inspect the spark plugs for excessive deposits that can glow and  pre-ignite the air/fuel mixture. Refer to 
Spark Plug Inspection 
. |  
  
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Engine Mechanical Checks 
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|     •  | Check for carbon buildup. Remove the carbon with a top engine  cleaner product. Follow the manufacturer instructions on the container. |  
  
|     •  | Check for incorrect basic engine parts such as the cam, the heads,  the pistons, etc. |  
  
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Additional Checks 
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|     •  | Check for a dirty air filter or a restriction in the air induction  system. |  
  
|     •  | Check for any Service Bulletins or updates. |  
  
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