Originally Posted by its840
i have a series II and on my fuel door it says "USE PREMIUM UNLEADED ONLY".
In fact from my owners manual
If you have a 3800 Supercharged engine (VIN Code 1), use premium unleaded gasoline rated at 91 octane or higher. With the 3800 Supercharged engine, in an emergency, you may be able to use a lower octane -- as low as 87 -- if heavy knocking does not occur. If you are using 91 or higher octane unleaded gasoline and you still hear heavy knocking, your engine needs service.