Gasly and Hartley both race the new Honda power unit in Friday’s practice.
While the Frenchman finished in eighth place, 1.752s off the pace in FP2, Hartley was P16.
However, overnight Honda have decided to run the older spec engine from Saturday’s final practice onward.
“Having studied all available power unit data after FP2, we realised that, although the performance was encouraging, there is still some work to do in some areas such as calibration and matching the power unit to the chassis,” explained Honda chief Toyoharu Tanabe.
“So we have decided to revert to the older specification power unit on both cars for the rest of the weekend.
“We believe we can complete the work before the Japanese Grand Prix, so that we can run the new specification power units on both cars from then on.”