I agree the buzz indicates the relay is working. You can have the fuel pressure tested. Fuel pressure leaks could occur at any number of locations in the Bosch fuel injection system. You can purchase a fuel pressure tester for $90 and DIY, or pay a shop $100 to preform the fuel pressure tests, to see if the fuel pressure is good. Don't rule out a lean mixture, or faulty device in the warm side of the fuel injection system. Once the engine warms up it calls for a leaner mixture, if you increase the fuel to air mixture, (richer more fuel) and you still cut out, I'd focus on the fuel system and not electrical. Now that I replaced my fuel pump the 5 sec buzz is not so loud. A word to the wise - once a fuel pump fails, it will leave you stranded.
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