[Christ]

Can't say, really. I've done it on carb'd cars, and never with EFI, that I remember. At least not in full or large quantity. Maybe a gallon or so at a time, in my Sunbird (Pontiac 2.0OHC non-turbo).

I've run 2-cycle gas at 32:1 in my Civic, as well. Smoked a little bit, but it smoked normally, so I can't tell if it was from the fuel or just normal smoke.

As little regard as I normally have for my vehicles, I've added all sorts of things to the fuel, just to find out what would happen.

Of course, if you add diesel, the engine will run differently, and EFI fuel pumps aren't really designed to lift and pump diesel properly, nor are the injectors designed to flow it properly. Adding it to gasoline is a big difference from just using it straight.

I have to assume that those owners (of rather expensive cars, which normally means that they're not too up to date on their car knowledge) just noticed that it wasn't running like it normally did, and pulled over and called a dealer/mechanic etc. I'm sure they were more afraid than rational at that point.

I'd also never trust a dealer to tell me what's wrong, since they're usually known for including things that have nothing to do with the actual repair.