The price differential for premium fuel has gotten out of hand. It now costs 34% more than regular. I remember the argument of false economy when going from 91 octane to 87 octane, but that was when regular was only 7% cheaper. That argument doesn't hold water anymore.


Would regular gas harm the 1.9L turbo engine? Does the 2002 S40 have a knock sensor?

 

Yes the Gen 1 S40s have a knock sensor and you should be fine running 87. All you lose is a bit of performance when at full throttle. I've been running 87 in my '00 S40 for years and have not noticed any issues. Consumer Reports just did a test to confirm but noted major brand Premiums do a better job of cleaning -and you get the benefit after 1-2 tanks. So I just run a tank full of premium every 10 tankfuls or so to get some detergent action.

 

You may notice some reduced performance since the computer will back off on timing advance and adjust other parameters based on the knock sensor. You may also see a reduction in fuel economy.