Ferrari were doing something clever/illegal where they were bypassing the FIA sensor which measures the fuel flow to the engine. More fuel equals more power. This seems common knowledge within F1 now.There's a thread called "Exeter on Sarries" on the "Northampton Saints Rugby Forum" which discusses the new book by the Guardian's Robert Kitson on the Exeter Chiefs which once again highlights the Saracen's outrageous behaviour regarding the breaches of the salary cap. Knowing your interest in Formula One I have brought it to your attention as one of the thread's correspondents claim that Ferrari cheated all last season and that it was something to do with the engine? By the way he talks it seems that those that control F1.com are just as secretive as was Premiership Rugby back in 2015 when salary cap discrepancies first came to light.
However FIA President Jean Todt (ex Ferrari) said that it wasn't possible to prove they had broken any regulations. So a settlement was made and a joint statement put out. Other teams want more information but Ferrari are adamant that it would infringe details of their intellectual property . Ferrari also say they have done nothing wrong otherwise they would have been disqualified from races last season.
The Ferrari engine was the quickest engine last season right up to the point when they started to be investigated after monstering Spa and Monza, two power tracks. Then they mysteriously seemed to lose power about the time of the US Mexican GP's which they were expected to win. This season their power output is nowhere which combined with a high downforce "draggy" concept, carried over from when the engine was putting out monster power, has seen them relegated to lower midfield. And there isn't much they can change next year either due to regulations.
Whether Todt is truthful and the FIA couldn't definitively prove Ferrari broke the rules, but knew they were, hence the settlement, who knows. The FIA is known as Ferrari International Assistance by many such is their power in the sport.
The investigation only came about due to pressure from other teams who suspected Ferrari were up to something. They are normally very good at working out what each other are doing and the FIA stepped in before a formal protest. Red Bull as usual for them did seek clarifications on certain engine issues which was when Ferrari suddenly lost power though. And now this season, the car is a donkey which will lose Ferrari millions in prize money, they are currently sixth in the constructors championship. Everyone drew their own conclusions .