Start the engine, block the end of the exhaust and without a leak the engine should stall.
With a leak the engine keeps running and you should be able to hear where it leaks.

But with the fuel consumption being about the same, I would say the cause is something different. Maybe a leak somewhere around the inlet manifold or a defective sensor.

Can your friend read live data? Then check the "Fuel Trims".
They should be close to 0%.