[Jonny042]

I do the odd calibration/test/repair/rebuild on MFI pumps and always recommend the owner add a wideband O2 sensor and gauge if they haven't already.

I would not own an MFI car without also having a WBO2 system. There simply isn't enough downside not to. Otherwise you are guessing. And not just for initial setup, for tuning along the way, and diagnosis of issues.

IMO if it's fouling plugs it's over-rich but you'll never know by how much!