How or what is the cause of Engine back firing

How or what is the cause of engine back firing.

Model: Elantra MD

Year model: 2012

Displacement: 1.8 cc

How or what is the cause of engine backfiring.

= This case for the Elantra new model first time for me to trouble shoot. i make road test to confirm the problem & for the engine to get the normal temperature. after a half an hour of engine running turn off the engine.immediately the problem occured means the customers problem confirm. check with the GDS ( Global Diagnostic System ) for the trouble code but there is no trouble code found then all current data also they are in good condition.

= I will try to barrow one good ECU and fixed then make another road test after half an hour turn off the engine. then the problem disappear.

=Replace new ECU.