Freddie's Regal said:Detonation and the EGR's role
1) Detonation is is an erratic form of combustion. Detonation occurs when excessive heat and pressure in the combustion chamber causes the air/fuel mixture to auto-ignite. This produces multiple flame fronts within the combustion chamber instead of a single flame kernel.
When these multiple flames collide, they do so with such an explosive force that it produces a sudden rise in cylinder pressure. This results in a sharp metallic pinging or knocking noise. The hammer-like shock waves created by detonation subject the head gasket, piston, rings, spark plug and rod bearings to severe overloading.
2) The Exhaust Gas Recirculation (EGR) system leaks small amounts of exhaust into the intake manifold through an EGR valve. Though these EGR gases are hot, they actually have a cooling effect on combustion temperatures by diluting the air/fuel mixture slightly. As well as reduce formations of NOX for emissions control, this results in a smooth controlled burn that prevents detonation.
3) A lot of people think that the EGR valve is just an emissions control device and remove it. Technically it is an emissions device, but it is a needed on our cars since it allows for the higher timing.
Detonation happened to my Regal when I used the wrong EGR valve. The lesson I learned I share with this forum. Although all our EGR's look alike, they are not.