The FIA gave the all-clear to all of Formula 1's engine manufacturers over fuel use after the Spanish Grand Prix, following its clampdown on trick systems.
As Motorsport.com revealed on Sunday, the FIA issued a technical directive to teams after qualifying at Barcelona to demand that fuel pressure remained constant above a flow rate of 90kg/h at all times.
It is understood that this move came amid concerns that some teams could be cleverly collecting fuel beyond flow meters, perhaps in flexible hoses that acted like balloons, to inject it into the engine when it would be of the biggest benefit.
Such behaviour would be evident by fluctuations in fuel pressure at maximum acceleration.
As one team insider told Motorsport.com: "The way the FIA can keep track of that is looking at the pressure in the system.
"If you were to do that, if you had a big 'balloon' on the other side and you dumped it out, the pressure would go down."
The FIA duly inspected the fuel pressure readings from each of the F1's four manufacturers in parc ferme at the end of the Spanish GP.
The FIA has indicated to teams that there will likely be careful inspections of all their fuel systems too at some point, to ensure that teams are not trying to exploit the rules.