What causes knocking, pinging, detonation, and pre-ignition? - Lexus IS Forum
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post #1 of 1 (permalink) Old 09-02-2004, 12:42 PM Thread Starter
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What causes knocking, pinging, detonation, and pre-ignition?

detonation and pre-ignition are about the same thing, they just happen at different times in the compression cycle. pre-ignition is either caused by hot spots that pre-ignite the fuel before the spark plug goes off or the actual compression of the air/fuel igniting the mix. remember, when you compress a gas, you heat it up. that's why too much boost can cause extra high cylinder temperatures and subsequent pre-ignition. a lot of people call this detonation, but it isn't. you can feel pre-ignition, it will feel like rough power. detonation occurs after the spark. if the air/fuel ratio is too lean, you don't get a nice progression of the flame front from the spark plug towards the bottom of the cylinder. the burn will be uneven, and you will develop many different flame fronts going in many different directions. as these flame fronts collide, they make noise and you hear the knocking and pinging. more importantly, the oxygen is going to react with something. better it react with gas than metal. both of these will lead to high EGTs. now hesitation can be caused by both lean and rich conditions. usually by too rich conditions. you basically flood out the spark and it doesn't light off the air/fuel mixture. this will lead to black smoke out the tail pipe and low EGTs. if you run too lean to get a hesitation, you will be way past the point that your EGTs should be sky high. another thing to check is make sure all injectors are firing. you should be able to do this at idle by putting a screwdriver on the injector and the other end butted up against your ear. or, you can sometimes feel them by putting the tip of your finger nail on the injector and pushing a little hard. the vibration is carried through the bone and you feel it.
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