I have a BS3 with 85# Siemens injectors on a ZZ502 with a Hogan sheet metal intake.

The issue I'm having is that the O2 sensor from the BS3 does not agree with the in-dash (wideband). You can tell something truly is wrong, because I have to set the idle fuel cell down to 11% VE to stop it from pulling fuel.

With one arrangement, I get the following:

BS3: avg 14.7 InDash: avg 12.5

If I switch the connectors (they're compatible sensors):

BS3: avg 13.5 InDash: avg 15.5

So clearly one side is reading far leaner than the other. I went around the intake mating surface with a propane torch (unlit but open) hoping to see a change in AF ratio somewhere, but didn't.

I'm guessing it has to be an intake or exhaust leak, but am sort of at a loss on how to narrow it down without just redoing everything.

Any sage-like wisdom on what to look for and how to test it would be very welcome!

Thanks,
Dave