problem with 2000 crown victoria!

ok my engine does burn gas and I think its the piston rings but once in a while I hear this DING sound and a plume of smoke comes out of the tail
pipe and the engine starts to have idling problems as if it wants to stall and sometimes it does. and this has been happening more often lately, was wondering what could cause this? are the piston rings getting so bad that the oil is getting way upthere where the spark plugs are and shutting them off? or is the the knocking/pre ignition everybody talks about(scanned the computer no codes regarding pre ignition) now I know I have pretty bad catalytic converters (still passed smog 3months ago) and a bad evap system but I really dont think these problems could be the cause of this. and btw how hard is it exactly to change piston rings on these it possible to do this without taking the engine out of the car. any help appreciated. thanks
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