Hi John, Have you checked the fuel pressure, I have just resolved an issue like you have with a BMW v12, and I even had the fuel rails off spraying the injectors into air all looked good, when exposed to the atmosphere, but not getting enough fuel when the injectors were installed in the manifold. It turned out to be a weak fuel pump some injectors did not get enough fuel depending on their position on the fuel rails. Have you also checked the fuel pressure regulator on the rails.
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