There IS water formed as a byproduct of hydrocarbon combustion, along with heat, light, and other gasses, such as CO and CO2, It's a physical FACT. Combustion in it's simplest form would be the combustion of pure hydrogen with pure oxygen (bad idea BTW, don't try at home). Basically, in it's elemental form, Hydrogen just chills by its lonesome, and Oxygen pairs up with a fellow Oxygen buddy (always follow the buddy system

) So, we have H+O2. Since we all know that for the bond to be stable, oxygen needs to find two valence electrons, we now have 2H+O2. Again, this won't work because we need to balance the equation. So, now we can get 4H+O2, because there are actually 2 oxygen atoms in the molecule. This equation will balance out to become 4H+O2=2H2O. Thus proving that water is infact a byproduct of combustion. Since I'm not sure of the chemical formula of Gasoline (or diesel if you prefer), I can't do the math for a hydrocarbon combustion reaction, but if anybody wants to do it out, this would just reenforce the fact.
I'm not a chemist, nor have I taken a chemistry class in about 3 years, so if anybody points out a mistake in my proof (and they know for sure), PM me with a solution and I'll fix it so I don't look st00ped.