I'm getting the same, I don't see any effect at all though it says GM-1 enabled.
I don't know if there is a connection, but back in the 4.11 guide it stated that "The Ta152 H-1 now has working GM-1 injection". However, when you activate boost, the display says MW50, not GM-1. Maybe they were trying a work-around there but overlooked it in the Bf109E-7/Z.
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