Engine Pings or Knocks

Normal Ignition:

Pinging, Spark Knock:

ENGINE PINGS OR KNOCKS

Description
Upon accelerating, the engine produces a knocking or pinging sound.

Explanation
Detonation (spark knock, or pinging) is the result of a secondary combustion occuring within the cylinder.

With normal ignition and combustion, the ignition spark ignites the fuel mixture and the combustion spreads evenly across the cylinder. When spark knock occurs, excessive heat and pressure or heated carbon particles ignite the fuel mixture concurrently with the ignition spark, resulting in two separate combustions within the cylinder. The two flame fronts collide, resulting in spark knock or pinging.

Spark knock produces extreme temperatures within the cylinder. Severe engine damage may result from prolonged spark knock.

Causes

Advanced Ignition Timing
Advancing the ignition timing increases the peak combustion pressure. The higher pressure increases the probability that spark knock may occur.

Testing
- Check Ignition Timing and advance.

High Compression or Increased Air Charge
An increase in compression or volumetric efficiency of the engine will result in higher combustion pressures. The higher pressure increases the probability that spark knock may occur.

Increased compression or increased volumetric efficiency may be from the following:
- High performance pistons or camshafts.
- Shaved cylinder heads or decked blocks (increases compression).
- Carbon buildup on top of the piston (increases compression).

Testing
- Perform a Compression Check
- Check to see if the cylinder head was resurfaced recently. Reducing the thickness of the cylinder head increases the compression ratio.
- Verify no performance parts have been added.

EGR Problems
The Exhaust Gas Recirculation (EGR) system is used to recirculate a small portion of the exhaust gas back into the cylinder. The inert exhaust gas displaces and disperses the air/fuel mixture, resulting in a lower combustion temperature. This significantly reduces the probability of spark knock.

Testing
- See Emission Control Systems for testing information. Emission Control Systems

Low Octane Fuel
An octane rating is proportional to the fuel's ability to prevent spark knock. High octane fuels require a higher temperature to ignite than low octane fuels. Spark knock is less likely to occur when using high octane fuel than when using low octane fuel.

Testing
- Verify the fuel octane rating is equal to or greater than the minimum recommended value.

Overheating
Low coolant level or engine overheating can result in hot spots occuring along portions of the cylinder wall and head. These hot spots can promote the occurrence of secondary ignition and spark knock.

Testing
- Check coolant level and verify correct type and concentration of coolant is in use.
- Check cooling system operation. See Cooling System. Cooling System

Lean Air/Fuel Mixture
Lean air/fuel mixtures result in higher combustion and exhaust temperatures. Higher cylinder temperatures increase the probability of spark knock.

Testing
- Check for vacuum leaks, inspect all vacuum hoses and gaskets. Diagrams
- Check fuel pressure.
- Check engine control system for proper operation. See Computers and Control Systems. Computers and Control Systems