Pistons are made with materials that is strong enough to withstand the heat of the engine, but pistons do fail. The signs of this of a piston failure can be engine noise (rattling or knocking sounds during engine idling), oil burning, misfiring and loss of power.
Loss of compression also can cause a misfire and a loss of power. Compression loss can happen if the engine has a burnt exhaust valve, a bent valve, weak or broken valve springs, a blown head gasket — or a bad piston. If a compression test reveals little or no compression in any cylinder, and a leak down test show compression is being extinguished into the crankcase and not out of the intake units or exhaust ports, it’s possible then that the piston has a hole in it or is badly cracked. Unless you have a bore scope, you will have to bring out the cylinder head off the engine so proper inspection of the piston can be done. However if the engine is burning oil and there is blue smoke in the exhaust unit, the problem may either be worn valve guides and valve guide seals, worn or broken piston rings, or even a badly cracked piston.
Diagnosing a Burned Piston
If on top of the piston there is a melted appearance, or it has a hole burnt through the top, the piston has been running very hot. Pre ignition or detonation has destroyed the piston. This is so because aluminum melts when the combustion temperatures get too high, so investigate whatever caused such a high heat.
Prominent among the causes of a burned piston is a dirty fuel injector that is getting way too lean. For some car, if you ever found any trouble codes like P0171 or P0174 that shows a lean fuel situation on the same cylinder bank as the bad piston, and there is likelihood that the engine has a dirty injector on that cylinder, and likely dirty injectors on the other cylinders too. The only sure way of knowing would be to pull all the injectors, clean them using a fuel injector cleaning machine, then flow-test all the injectors and check the results. Any injector that does not have within 5 to 8% of flow rate should be replaced.
But if you don’t own a fuel injector cleaning machine with a flow tester, what to do would be to replace the injector on the cylinder with the burned piston, then clean the rest of the injectors and then the engine would be back together and running again.
Other conditions that can lead to a burned piston include; the wrong heat range spark plug (very hot for the application), over-advanced ignition timing (not very common with today’s electronic spark controls), a bad knock sensor that failed to signal detonation, low octane fuel (bad gasoline that doesn’t meet a minimum octane rating of 87, or someone using 87 octane gas in a high compression engine that requires premium fuel), or any factor that would cause the engine to run hotter than normal the normal level inclusive of low coolant level, bad thermostat, weak water pump, cooling fan that isn’t working, or a clogged catalytic converter that is creating a restriction and backing up heat in the engine.
On turbocharged or supercharged engine, too much boost pressure and/or not reduced fuel can burn a piston very quickly. Check the working of the waste gate and boost control system. If the turbo system has been tweaked to deliver higher-than-stock boost pressure for more power, the turbo may be pushing more air into the engine than the stock injectors can use, causing the fuel mixture to lean out and burn the piston. Whatever the case, visit your technician.