Only car #1 slows down when empty

That's how it works.

Fuel = ON means the car remembers how much fuel it has. That's cool and all, but it's just a number. It doesn't actually affect how the car drives. For this kind of fuel, the amount of fuel in the tank stays in the car, no matter what ID it's on.

Fuel = Real means the CU controls how much fuel each car has, because it can also change how much power the car has depending on how much fuel it has. For this kind of fuel, the tank stays with the ID, not the car.

It's possible that I'm not understanding your explanation, but you might not have performed your test correctly.

With Fuel = ON (not Real), drive a car programmed to ID #1 until it runs out of fuel and slows down. Then, program that car to ID #2 and run it. It should be slow because it's out of fuel. Pull into the pit and refuel. Now, program the car back to ID#1. It should behave as it would with a full tank. This is because the CAR stores the fuel level in this mode.

With Fuel = Real, drive any car on ID #1 until it's out of fuel. remove that car, and put another car in it's place. Does it also drive as if out of fuel? Refuel it. Then, put the original car back on. It should now drive as if it has a full tank. This is because the CU stores the fuel level in this mode.

Now that I've said that as if I'm 100% sure I'm correct, I will say that I'm not 100% sure, and that I hope anyone with confidence will either corroborate that, or explain that I'm wrong.

The Ferrari is likely being slowed- but it has a FET that hides it.

Fuel use on Carrera is not that complicated. On a Black Box system (been over ten years now since they were sold), or a CU w/o a pit lane adapter track (again- ten+ years since pit lanes didn't include one of those), the car chip tracks fuel. Can't be reported to software, and there are likely third party chips that won't track fuel use.

On a CU system with a PLA- which is anything built and bought in the last ten+ years- the CU tracks fuel, the car chip does not, so fuel levels can be reported to software, and the car chip doesn't have anything to do with it. Fuel switch set to ON means fuel is turned on. Fuel switch set to REAL means fuel is turned on, and the CU will change a car's driving behavior to simulate the weight of fuel in the tank.

That's pretty much it.

The slowing of empty cars and flashing of lights does differ from PLA equipped systems and non-PLA equipped systems. But the latter are so rare, and their owners are so used to using them (after 10+ years) that it isn't worth going into.

Interesting Bruce about the PLA systems, but I won't ask

Some info on cars that have FET issues...

The car decoders from the manufacturing line up to late 2018 are mostly OK. (It only became an issue in late 2018)

Car decoders from the start of 2020 are ok.

There was a period where they were not. There is a list of affected cars on another forum but...

Here is a link with the details that you may need to fix a decoder that is affected. Hopefully your retailer or distribution channel can help you but the link might be of help otherwise. There is another thread but probably not recommended if you haven't already followed along (it goes on for many pages) The fix uses a 2cent part.

One little thing that isn't mentioned in that link is that the resistor needs to be packaged on the board as tightly as possible to fit back into the chassis of some cars. Smaller resistors are better for the fix if you can find them.