hi just reading around the old posts .
I managed to get the AI to do the pit by changing the fuel tank capacity.
Let me explain
(en isn't my first language sorry about that)
As you know in AC the AI pits only if it runs out the fuel. The only way to do it is reducing the tank capacity.
You need to duplicate the car first and tune the tank capacity.
How to set the correct liters?
Test how many liters you need to run for example 10 laps.
Assuming you need 50 liters to complete 10 laps in the AI car you set the fuel tank 3 or 4 liters less.
With this setting the AI cannot complete the 10 laps hence they will pit. The good is any car will have a different fuel load and different strategy.
I have tuned the car manually(unpacking the data) but someone in my league suggested to use Assetto corsa car tuner here in RD.
So if you have a campionship you need to know how many liters you need per track and modify the AI fuel tank accordingly.
Enjoy
Edit: to see the liters in the others cars when in the grid click CTRL+1 or CTRL+3 to scroll the AI cars.