Hey guys a friend and I were talking about different grades of gas and got to wondering about what causes pining in the engine. He thought that if you used to high a grade octane in your engine the fuel will burn to fast and cause the pistons to slap, causing a ping noise. Is this true? If not, what does cause pinging???

Thanks,
Christian

 

The higher the octane of the fuel, the more resistant it is to pinging, or premature detonation (caused by pressure or hot spots in the cylinder).

So, the higher the compression ratio of your engine, the higher the octane requirements.

Putting premium in an engine that runs fine on a lower grade is a waste of money, and actually can cause it to run less efficiently.

Pinging can also result from having a fuel mixture that is too lean, or when your timing is advanced too far. Generally, you want an A/F ratio of around 12.7:1, at a timing advance that is just shy of the 'ping threshold' to get maximum performance at wide open throttle. When the car is in cruise, the computer aims for an A/F ratio of around 14.7:1, which is considered the most fuel efficient and emissions friendly. The computer accomplishes this by monitoring intake air temp, and oxygen sensor readings (amongst other things). When you go wide open throttle, the computer more or less ignores the whole emmisions issue and aims for the richer 12.7:1 ratio. The engine also employs knock sensors which retard timing when the engine begins to ping.

F

 

What he said! Some C5s seem to develop carbon deposits that cause trouble. A "de-carbonization" process may clear it up. A dealer can do this, or do a search; there have been postings about doing it yourself. :)

 

Thanks Guys, this is why I love this forum, I get the full answer, not just a little itty-bitty one.

 

I'd sure like to touch on this just a bit more. I think I understand all of the issues noted so far, but what would be the most likely cause for pinging to start just all of a sudden? This car has never pinged, always been feed the good stuff and through the last two tanks of gas (from different places) the pinging continues. It pings at freeway speeds with the least bit of throttle and it pings at WOT. I know this can't be too good for the car and hate for it to go on for longer, but I want to see the dealer as a last resort. Your words of wisdom would be greatly appreciated. :cheers:
Thanks!

 

Dirty injectors can make it do that. :smash:

 

Pinging is caused when the expanding flame front from the spark so compresses the mixture at the other side of the combustion chamber that it spontaneously ignites. Pinging can also be caused by a buildup of carbon deposits that ignites the mixture in a similar manner.

Detonation is caused when the mixture spontaneously ignites before the spark.

So pinging, while detrimental to the engine, is NOT as dangerous as detonation--because pinging only uses a fraction of the mixture, while detonation uses the entire chamber-full.

Things to look for: insufficient Octane; fuel filter; dirty injectors; PCV; carbon buildup in the combustion chambers.

 

to high a grade octane in your engine the fuel will burn to fast and cause the pistons to slap, causing a ping noise. Is this true?

No, the fuel burns slower as the octane rating goes up. Spark plugs in a 'too hot' heat range can cause pinging too. I think most non-computer related(chips, tuning, etc) pinging is caused by carbon hot-spots inside the combustion chambers. An "Italian tune-up" may help this problem.....

Dan

 

Or any number of sensor/PCM failure or miscommunication.

A dealer (I know...I resist them as well) should be able to diagnose
very quickly.

...GeorgeC

 

Good info! What is the difference in sound of ping and knock? Last week I advanced my timing (hypertech III) and got a little bit of noise past 4k RPM. Only at WOT. It didn't always do it. But I only tried a couple of times. I detuned and it went away. It might have been my imagination. How noticable of a noise is it?

Can I keep the advance (one program, not adjustable) and goto colder plugs? What damage is being done to the engine under ping and knock?
Thanks

 

Surprisingly:

Pinging sounds like--well--ping ping ping
Knock sounds like--well--knock knock knock

Pinging is the sound of a stressed metalic component that has been hit with a sharp blow. The pinging is the metalic object resonating (like a bell) after being hit.

Knock is the sound of a high pressure rise in the combustion chamber that doesn't quite qualify as a sharp enough blow to initiate pinging. Knock sensers read the shape of the combustion "noise" and adjust spark timing to just abrely avoid knock. Maximum power is produced just below the knock threshold. Triffling/zero damage occures at low to moderate knock levels (unless the engine was specifically underbuilt--which corvette engines are NOT).

Under certain situations, knock can induce pinging. Knock is a (more or less) normal combustion process that has been timed with too much advance (typical). The smoothly advancing flame front goes chaotic and combustion proceeds more rapidly than desired. Thus, the abnormal pressure rise. When the pressure rised to maximun BEFORE TDC, the energy of the (too fast) combustion actually reduces the output of the engine (works against power production). Thus, setting advance is a tricky science in and of itself.

Pinging is an uncontroled explosion remote from the smoothly advancing flame front originating at the spark. when the exploding flamefront meets the smoothly advancing flame front, a shock wave is produced. This shock wave is the sharp impulse the "rings the bell"--so to speak. The typical component to ring is the crown of the piston, and the rods. Under damageing conditions, the crank may also begin riging.