Hi Gino
I do not know if the 406 V6 is the same as either of the 605 V6 engines. Maybe somebody in the group knows? However, the 605 V6 was developed ca 1988 by PSA with Renault and Volvo. The engine codes are ZPJ (12 valve) and ZPJ4 (24 valve). If the 406 V6 engine is similar, you will find 605 repair instructions on eBay. You can use the Haynes 406 manual for the rest ...
Hope this helps
Ivar Petur