AFAIK, the resistor is what selects a tune in the 14CUX, hence the name "tune resistor". It doesn't have a direct effect on fuelling, only which map the 14CUX reads, and this depends on the emission requirements of the particular market.
AFAIR I fitted a UK tune +cat to mine when I fitted the O2 sensors as again AFAIR this tune resistor activates the input from the O2 sensors.
Regards Philip A
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