I test drove a '97 XK8 today with 60k miles. For the most part, it was ok but a few times I heard a bit of pinging under load. Idling, the engine was smooth and quiet.. there didn't seem to be that much power though, to be honest.. it was there when I stomped on it, but I was expecting more. My '03 530i felt faster than this car.. but since this is the first XK I've driven, it's possible this is just it's characteristic. I'm going to try to find another one to take for a spin to see.

Anyway, is the pinging a serious issue, or is it something relatively minor to address? Knock sensor?

 

Mine pinged a bunch under load, then I found it had a moderate air/vacuum leak in the air tube (post-mass air flow sensor) so when it sucked in unmetered air, it ran lean and knocked. After fixing all of the air leaks (there were a few small ones, added up), and running good fuel, a clean MAFS and throttle body, tightened up throttle body cable, and she was instantly back to her old self.

 

+1 to H2Oboy's thoughts.

Cars on a sales lot sometimes have crappy old gas in them, especially if they have been on the auction circuit, and the tanks are never full, picking up condensation over time. I'll bet a tankful of quality premium and a good dose of Techron will make a difference.

My 2000 XK8 runs much better on premium Non-Ethanol fuel. You can look at Ethanol-free gas stations in the U.S. and Canada for a stateside/Canadian listing. In my area it is actually cheaper than premium ethanol-laced gasoline by 6 cents/gal! It is sometimes called "Recreational Gas" and found near marinas or other motorsports areas.

Here in the U.S., 15% ethanol is coming. Ethanol-free gasoline might become more popular after that as anyone with small engines like chain saws, mowers, motorcycles, boat motors, personal watercraft, older cars/trucks and the like wlll need better gas.

I rebuild personal watercraft carburetors at our shop and can tell immediately when someone was running cheap fuel. Stiffened diaphrams and even rust in the carburetor body itself is common. We get $150 per carburetor to bring them back to life - that buys a lot of fuel for 3-carb. small engine!