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i agree with most if not all of what pete said.
Pete what do you mean by no.4 i assume he's running FI turbo by the looks. definetly leanign out unless you had a boost spike from #338 4600rpm goes from 13psi to 19 and thats when your AFR start getting messy should be around 11-12:1 at max psi.
Really need some more details on what setup you got krawczuk is it a 3 bar map sensor? wideband O2? turbo setup and what sort of boost its running