Two cars were badly damaged at the Australian Grand Prix, with Nick Percat's Mustang catching fire at the start of Friday's race, before James Courtney's did likewise on Saturday.
Emergency meetings on the Saturday night led to a number of technical changes being implemented for the Sunday race, as well as a move to a safety car start, as part of a wide-ranging mitigation plan.
The series has since undertaken more targeted forensic work to pinpoint the cause of the fires. Autosport understands that the venting of the catch can will now be shifted further back in the car to limit vapour build-up in the engine bay.
In the previous specification, the catch can vented through a filter directly into the bay near the left-front wheel well.
It appears that the vapour build-up was the fuel for the fires, with ignition likely to have come from the red-hot exhaust hardware during a standing race start.
The venting was modified at Albert Park as part of the mitigation plan and will be further modified ahead of Perth in what is hoped will be a permanent solution to the problem.
The change is expected to allow a return to standing starts for the three races at the Wanneroo circuit at the end of this month.
This is not the only change to the cars ahead of Perth, with strengthening measures for the rear part of the chassis also being implemented by most teams.
Centre of Gravity testing, meanwhile, is thought to have yielded a very close result and is not expected to lead to any major changes to the new-spec cars.
