Still no luck.. checked the fuel injectors by let them spray seperately. No difference when you look at the spray pattern.

Interchanged the injector from 2 and 3. Still overfuelling at cylinder 3.
Interchanged the ht leads from 2 and 3. Still overfuelling at cylinder 3.

This morning started the engine when cold and again no problems even after about 10 minutes at idle. Then took a small ride. At first no problem but after about 10 minutes it started running on 3 cylinders. After checking spark plug 3 again this was completely wet.

So the problem is not in the injector, spark plug or ht lead from number 3.

I am thinking does it occure that inside the L8 ECU a transistor is failing when getting hot?
Or maybe it could be in the distributor cap that after a few minutes it stops sparking number 3. (checked this cap and cleaned it without any result).

Finally when the engine was hot I measured the resistance of the CTS at 510 Ohms. Is this a good value?