sync state 0

e46 m3 infinity with plug and play harness getting a sync state 0 after replacing head gasket and disconnecting the ecu. spark and injection probability are both 100%. any ideas?

Nothing specific, sorry, but the usual cause of such issues is a missed connection when refitting everything - including those that may have been pulled out by being caught on something being removed, an incorrectly refitted connection - even transposed but usually they're colour or shape coded, a faulty connection - sometimes the pin(s) can be pushed back into the connector body, or the wiring was damaged during the removal/refitting - there may even be one pinched between refitted components.

Before worrying about anything else, make sure there isn't a simple remedy for the issue.