Detonation/Spark Knock
Checks
| Action
|
DEFINITION:
A mild to severe ping, usually worse under acceleration. The engine makes
sharp metallic knocks that change with throttle opening.
|
Preliminary Checks
|
| • | Road test the vehicle and determine the severity of the complaint. |
|
Cooling System Checks
|
| • | Check for any obvious overheating problems. |
| • | Check for a low engine coolant level. |
| • | Check for a loose water pump belt. |
| • | Check for restricted air flow through the radiator, or restricted
coolant flow. |
| • | Check for a faulty or incorrect thermostat. |
| • | Check for a correct coolant solution. The solution should be a
50/50 mix of anti-freeze and water. |
|
Sensor Check
| Check for an Engine Coolant Temperature (ECT) sensor that has a shifted value.
Refer to
Temperature Versus Resistance
.
|
Fuel System Checks
|
| • | 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 greater than 20%. |
| • | Check for poor fuel quality and proper octane rating. If the scan
tool readings are normal and there are no engine mechanical faults, fill the
fuel tank with a premium gasoline that has a minimum octane rating of 92
and re-evaluate vehicle performance. |
|
Ignition System Checks
|
| • | Check the spark plugs for the proper heat range and gap. |
| • | Check the ignition timing. Refer to Ignition Timing Procedure. |
|
Engine Mechanical Checks
|
| • | Check for carbon buildup. Remove the carbon with a top engine
cleaner. Follow the instructions on the can. |
| • | Check for incorrect basic engine parts such as cam, heads, pistons,
etc. Refer to Engine Mechanical. |
| • | Check for excessive oil entering the combustion chamber. |
|
Additional Checks
|
| • | Check for the proper operation of the air induction system. |
| • | Check the Service Bulletins for any updates. |
|
