The Fuel would be delivered at about 1/2( Injector Latency will be wrong).. but the Load Calculation ( Called V.E. in Some ECU's Documents ) for the Engine would be incorrect, as it's a function of the Air Flow at a certain RPM, and the measured air flow is now 1/2, so the ecu will think the engine has NO load on it and the Calculations for the Ignition Advance will be wrong.
That is what I can think off off the top of my head..