7747 ECM what BLM target number for Stoich 14.13 AFR?

[EagleMark]

Would an exhaust leak cause this?

Yes!

[babywag]

Yes!

Well then there I have it(hopefully).
A few months ago I noticed the familiar noise that may be a leak on the driver's side manifold.
The o2 sensor bung is ~3" down from the manifold.

I'll pull it/get it resurfaced, and see what happens.
If that's not it, not sure what else the cause would be?

I've got it tuned by fudging the numbers, so @ least the engine runs right and won't melt a piston.
It was pretty damn lean! when I logged it on Sat. & much better this morning.
Basically I converted w/ 120 BLM for a target, and it went from ~16.x AFR to ~14.x AFR
Since I can't get the WB into the datastream have to guess a little.