Engine Pinging

This document relates to petrol engines in general and is not specific to PEUGEOT.

What is pinging?

Engine pinging also refered to as pinking, detonation or knocking

Pinging can be anything from a loud knocking noise to a soft tinkling sound that is emitted from the engine. If an engine has a tendency to ping, it usually becomes first audible when operated in the lower rpm range and during acceleration. Pinging tends to fade away with increasing engine revolutions.

What causes pinging?

An engine can ping for many different reasons. Here is a list of the most common causes for pinging starting with the most popular ones.

Fuel octane rating too low.
Compression too high. (usually caused by carbon build up inside the combustion chambers)
Over heating of the engine or just an individual cylinder. (Hot spots)
Knock detector faulty.
Ignition timing over advanced due to incorrect setting or erratic ignition due to a worn distributor. Most modern engines no longer have distributors.
Blocked exhaust, giving a high backpressure. (A significant loss of performance will be noticed)

Note: The tendency to pinging is highest when the engine runs on the ideal air fuel mixture. (14:1) Therefore a mixture problem -running too lean or too rich- will not cause engine to ping.

What happens inside the engine?

In the normal combustion, process the flame front moves at a speed of 10-20m/s with a maximum pressure of 30-40 bars. In the case of a pinging engine, the combustion speed is too high. After the spark plug ignited the mixture the pressure front moves up to 12 times faster then normal. This causes an excessive increase of pressure and temperature inside the combustion chamber. This high temperature will cause the yet unburned portion of mixture to self ignite and further accelerate the combustion process. This secondary combustion is what we can hear as the so-called pinging.
Note: Pinging is not an explosion it is merely a very fast combustion, which exceeds the healthy limits. The propagation of an explosion's pressure wave would be far higher,
something like 2000m/s. (m/s = metres per second)

Fuel Octane.

In order to slow down combustion we need a good quality, high-octane fuel. To keep it simple, high-octane fuel burns slower then low octane fuel. Special additives have to be blended with the distillate in order to achieve the required properties.

PEUGEOT recommends 95 RON fuel octane minimum.
We recommend: MOBIL Premium 8000 or SHELL Optimax.

Factors that reduce the pinging.

Higher octane fuel
High engine revolutions.
Low load.
Lowering of compression. (removal of carbon)
Mixture adjustment. Richer or leaner, away from the ideal ratio.
Fuel with higher flame point.
Retard ignition timing.
Low air density
Lower operating temperature
Cooler induction air

Consequences of pinging

Pinging can lead to damage, or in the extreme case, destruction of pistons, bearings and valves. This would only happen in a situation where severe and prolonged pinging is allowed to continue. Please don't panic if you hear some pinging. Today's engines are very robust. Some pinging that occurs occasionally will not harm the engine.

My engine started to ping, what should I do?

1- If it started shortly after filling up the tank, you have probably been sold a bad load of fuel. You can add an octane booster and drive the car until the tank is nearly empty. Now fill the tank with a premium fuel (MOBIL 8000 or SHELL Optimax) and see if the pinging disappears.
2- The pinging started after the vehicle has not been used for a long time. After one month or more the properties of fuel, start to change significantly. Take the same action as above. Wait for the next refuel and see what happens.
3- Should, however, the pinging be accompanied by poor performance and overheating? We recommend you contact your mechanic or dealer and have it checked.

Source: PEUGEOTLOGIC.COM