iv a misfire that gets worst when hot and only under load... iv changed plugs set gaps and replaced coilpacks

im only getting this misfire on 1 port which is passenger front...iv a coilpack tester which test voltage and arc... and its up and down almost fools you that's its ok but you wait and it misses....

iv changed coilpacks around and changed plugs...its always same port...

checked for fault codes and only get code 42 which with a chipped ecu iv been told is most likely a dummy code.

what else could it be...?? im convinced its electrical...as car runs spot on when it gets its spark...

 

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