what causes an engine to knock/ping?

[BlahBlahYouToo]

say you're running the proper octane and your engine still pings.
what exactly is the cause of it?

 

[sjwaste]

Many things can be the cause.

Check ignition timing, too much of an advance will bring about knocking.
Overly lean fuel mixture, which has a laundry list of causes on its own.
Wrong spark plug heat range (ignore if you're running a stock engine w/ factory plugs, this isnt your cause)
Any sensors or ECU issues leading to one of the above.

It can go on and on. What year/make/model/mileage? What's the current state of (dis)repair?

 

[BlahBlahYouToo]

Originally posted by: sjwaste
Many things can be the cause.

Check ignition timing, too much of an advance will bring about knocking.
Overly lean fuel mixture, which has a laundry list of causes on its own.
Wrong spark plug heat range (ignore if you're running a stock engine w/ factory plugs, this isnt your cause)
Any sensors or ECU issues leading to one of the above.

It can go on and on. What year/make/model/mileage? What's the current state of (dis)repair?

sorry, didn't specify that it was a general question.

 

[sjwaste]

Originally posted by: BlahBlahYouToo

Originally posted by: sjwaste
Many things can be the cause.

Check ignition timing, too much of an advance will bring about knocking.
Overly lean fuel mixture, which has a laundry list of causes on its own.
Wrong spark plug heat range (ignore if you're running a stock engine w/ factory plugs, this isnt your cause)
Any sensors or ECU issues leading to one of the above.

It can go on and on. What year/make/model/mileage? What's the current state of (dis)repair?

sorry, didn't specify that it was a general question.

Ah, in that case, the most general causes would probably be ignition timing or faulty fuel delivery. Usually the fuel delivery issue will manifest itself more so at higher loads and higher RPM. Ignition timing could be anywhere across the RPM band.

 

[Toastedlightly]

well, pinging is caused by the piston vibrating inside the cylinder. This is caused (most typically) by the fuel mixture being ignited too far before top dead center (BTDC). The fuel mixture presses down, while the piston is being forced up. The energy is transferred to the piston which then vibrates.

Running lean also causes this condition. When running lean, the spark plug and carbon deposits become extremely hot. If they become hotter than the autoignition temperature of gasoline, the gasoline will ignite too far BTDC, causing the same situation.

 

[mooseracing]

Too high of compression for the octane level of gas, which most people/computers bandaid it by reducing the timing.