Mac the knock

Fuel injector in cylinder 1 showed up malfunction in december. Got my mechanic to replace it, recalibrated and erased the faults. All was running 100%.

8 weeks later here i am back at the mechanics with the same fault showing on the ecu code reader: electrical malfunction in cylinder 1. At the moment he has the injectors exposed and cleaned. All the wiring and connections have been double checked but this fault is still showing.

Would it be possible that the loom is the cause of this??
Has this ever crossed your path before??

Trying to get this sorted without too much expense.

Thanks for your help!