While the top GT500 division has been using CNF since the start of the season, problems for some GT300 cars using the new ETS Racing Fuels-supplied product during pre-season testing prompted series organisers GTA to delay its introduction for the lower class.
A two-day test was held at Suzuka following the most recent race at Fuji earlier this month to give the GT300 teams another chance to validate improvements made to the fuel in recent months.
However, a brief statement issued by the GTA on Friday saying that the decision has been made to postpone the switch to CNF again to give teams further time to iron out problems with the cellulose-based fuel.
The statement did not specify a new target date for it to be implemented, meaning the GT300 class will continue to run on regular gasoline until further notice.
"Regarding the implementation [of CNF] for the future, we will continue to discuss it with the parties concerned," it read.
While the GT500 class has raced without significant problems using CNF since the start of the season, Toyota, Honda and Nissan were all involved with bench testing at an early stage and are all running similar inline four-cylinder, turbocharged power units.
By contrast, the GT300 division features a wide variety of engine types, ranging from Subaru's WRC-derived boxer four-cylinder motor to the 6.2-litre normally-aspirated V8 in the Mercedes-AMG GT3.
One of the issues teams have reported is related to oil dilution, which can have an impact on the engine's mechanical reliability.
Strict homologation rules for FIA GT3 cars also make it harder for engines to be modified to combat these issues.
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