Sounds temp related. O2 sensor won't normally kill an engine; if you want to eliminate it, disconnect it and see if the problem stays.

How full is your gas tank?

Have you tried bypassing the OVP or FP relay? When you turn the key to on (but not crank)

When it won't start, do you turn the key to "run" (but not crank) and listen for the pump to come on for 2 seconds? If you apply 12V directly to the pump, does it run? Will it start/run with the pump powered like that?

Have you checked to see if the cold start injector for leaking or possibly not shutting off?

Have you checked your coolant temp sensors against known values?

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.