Ok, today I did the sby battery test on Version 6.0 and I can see on the datalog that the EGT´s are going down during this 45 minutes all the same.
When doing a Mag check, also in flight, the engine runs normal with increasing EGTs (all of them), this would exclude the spark plug thing.
Remains the injector. I have to swap the sensors to see. But before the replaced sensor was showing too low a EGT it was always inline with the others. Personally I suspect the sensor but a swap should show the truth.