Originally Posted by Alan G

Thanks for all the replies so far lads. Some great info being brought to the table. Unfortunately, I don't have an AFR plot, however I was advised to check electrical components / sensors as he was happy with the fueling when boosting etc. We also checked voltage to the pump and it was spot on.

To rule out the chip and ECU we swapped out the ECUs with another L6 (both are running the same spec chip from MSD) and the same problem was seen with both!