I have a 2004 coupe g35 sitting at 150,000km. the 1st time my car started to back fire, we replaced the coils and sparkplugs since they were burnt also which left a hole in the driverside cat. 2 weeks after the car started to backedfire on me again. I towed the car back to the shop and another mechanic came and said it was the ECM that was giving the problem, so then we replaced the ecm, reprogrammed it, replaced the coils since it was still under warrenty and replaced the driverside cat with a used cat which was in good condition. parked the car for winter and brought the car back out yesturday. did the emission, passed the test and while driving back home, my car started to backfire again.

If anyone knows why this is keep on happening or came across this issue, please let me know. I would really appretiate the help and feeback. thanx

 

^ mostly replacing plugs and coils takes car of the backfiring, seem slike you covered everything that could have gone wrong, hope someone with more insight will drop by and help you out.

BTW you will be able to get a better response by posting this in the 1st gen G's forums cause there are more ppl with older G's with such high miles and might have had such an experience unlike most low-mid mileage 2nd gen G's here.