The stock MR2 fuel pump wiring is likely 30ft long with multiple junctions, providing lots of opportunities for voltage drop to the pump. When installing anything larger than a Walbro 255, we add a Fuel Pump Relay Upgrade in the frunk to send voltage straight from the battery to the pump.

If you decide to DIY instead, be wary of cheap relays and fuse holders, as they often cause issues down the road. Resistance makes heat, which makes more resistance. This melts things.