[v8Toilet]

Mine will ping on 87 octane under hard acceleration or when under a load in overdrive or when it shifts sometimes. With 89 octane it hardly ever pings except on very hot summer days under hard acceleration it sometimes pings. It never pings with 93 octane available here in the northeast. Now if you suspect you have a leaky valve you can test that with a vacuum gage.

I posted some information talking about detonation vs. pre-ignition to help clear up why your ECU might not be able to control it like many people say it should. This is of course assuming you don't have a defective knock sensor. Either way even if your engine has a good knock sensor it is still susceptible to pre-ignition and it still makes less power with 87 if the computer retards the timing due to low octane resistance in your engine.

Here is what I wrote.

Originally Posted by posted by V8toilet

Mine would ping on 87 momentarily under initial heavy throttle and then stop. When I use 89 octane it doesn't do that or I don't hear the bb noise for that short period of time when I give it allot of throttle.

Ping is nothing more than the fuel self igniting under the extreme temperatures of combustion. As the air fuel mix is compressed and the spark plug fires sometimes the flame front causes the fuel that is not burnt yet to compress even more and then start another flame front in the combustion chamber. These two flame fronts then collide and push on the piston unevenly. You hear this as a noise that sounds like bb's in the engine. This is called detonation. There is another thing similar to that called pre-ignition that is caused when the air fuel mixture self ignites before the spark plug ignites it because as the air fuel mixture compresses it, it heats up.

The only difference between 87, 89, 91, and 93 is that 87 octane fuel is more prone to detonation than 89 is and 89 is more prone to that than 91 is and so on. The higher the octane rating the higher the flash point of the fuel is. The flash point is the point of which the fuel self ignites.

Now if you use 87 and your engine experiences detonation than the knock sensor is supposed to pick that up and retard ignition timing. This lessens the cylinder pressures and thus stops detonation from happening. The only ramification of having less ignition timing is that you loose engine torque and mileage with less ignition timing.

Now if you do hear the bb noise than what you might be hearing is pre-ignition since the computer manages detonation. The computer can’t stop this from happening because ignition timing has much less to do with it. Pre-ignition is cause by the heating of the air fuel mixture from compressing it. If you compress a gas it gets hot. If it gets hot enough to reach the gases flash point than it self ignites and you get the bb sound. The computer might read it and retard the timing but it won’t matter because the fuel is self igniting without the spark involved.

Elevation does affect this because at sea level your engine takes in more air and thus more fuel due to the greater atmospheric pressure. The more air and fuel that your engines compresses in that cylinder the hotter it’s going to get because it’s compressing more air and gas into that same tiny space now. When you are in the high elevations your engine is taking in less air and fuel and so it compresses less air and fuel into that same space and thus it gets less hot. Higher elevation on a high compression engine has the same effect as a low compression engine at sea level. It compresses the air and gas mixture less!

Doing engine modifications can also make your engine more susceptible to pre-ignition and detonation. This is because breathing modifications like headers and intakes cause your engine to take in more air, which the engine than squeezes into that same small combustion chamber and because it squeezes more air and fuel into that same space it gets hotter.

If you want to stop it either be gentler on the gas pedal or use a higher octane fuel until it stops. Some engines in the same family will require higher octane’s than others. I know that the Lexus versions of the 4.7-liter V8 require a higher octane fuel than 87.

Mine would ping on 87 momentarily under initial heavy throttle and then stop. When I use 89 octane it doesn't do that or I don't hear the bb noise for that short period of time when I give it allot of throttle.

Ping is nothing more than the fuel self igniting under the extreme temperatures of combustion. As the air fuel mix is compressed and the spark plug fires sometimes the flame front causes the fuel that is not burnt yet to compress even more and then start another flame front in the combustion chamber. These two flame fronts then collide and push on the piston unevenly. You hear this as a noise that sounds like bb's in the engine. This is called detonation. There is another thing similar to that called pre-ignition that is caused when the air fuel mixture self ignites before the spark plug ignites it because as the air fuel mixture compresses it, it heats up.

The only difference between 87, 89, 91, and 93 is that 87 octane fuel is more prone to detonation than 89 is and 89 is more prone to that than 91 is and so on. The higher the octane rating the higher the flash point of the fuel is. The flash point is the point of which the fuel self ignites.

Now if you use 87 and your engine experiences detonation than the knock sensor is supposed to pick that up and retard ignition timing. This lessens the cylinder pressures and thus stops detonation from happening. The only ramification of having less ignition timing is that you loose engine torque and mileage with less ignition timing.

Now if you do hear the bb noise than what you might be hearing is pre-ignition since the computer manages detonation. The computer can’t stop this from happening because ignition timing has much less to do with it. Pre-ignition is cause by the heating of the air fuel mixture from compressing it. If you compress a gas it gets hot. If it gets hot enough to reach the gases flash point than it self ignites and you get the bb sound. The computer might read it and retard the timing but it won’t matter because the fuel is self igniting without the spark involved.

Elevation does affect this because at sea level your engine takes in more air and thus more fuel due to the greater atmospheric pressure. The more air and fuel that your engines compresses in that cylinder the hotter it’s going to get because it’s compressing more air and gas into that same tiny space now. When you are in the high elevations your engine is taking in less air and fuel and so it compresses less air and fuel into that same space and thus it gets less hot. Higher elevation on a high compression engine has the same effect as a low compression engine at sea level. It compresses the air and gas mixture less!

Doing engine modifications can also make your engine more susceptible to pre-ignition and detonation. This is because breathing modifications like headers and intakes cause your engine to take in more air, which the engine than squeezes into that same small combustion chamber and because it squeezes more air and fuel into that same space it gets hotter.

If you want to stop it either be gentler on the gas pedal or use a higher octane fuel until it stops. Some engines in the same family will require higher octane’s than others. I know that the Lexus versions of the 4.7-liter V8 require a higher octane fuel than 87.

Now it’s also possible that your engine could have sharp edges in the combustion chambers from the machining process that get very hot and glow red. These red hot sharp spots from the machining process will cause your engine to suffer from pre-ignition no matter what octane you use. The wrong spark plugs could also cause that! Excessive carbon buildup also will cause your engine to have pre-ignition as excessive carbon buildup can get red hot too just like sharp edges in the combustion chambers.