You can use just about any amount you want. I've used a quart in 1/4 - 1/2 a tank of gas. It won't hurt anything. I don't think more than once/year is necessary. This type of chemical is prone to forming soot on combustion so don't use it all the time or during an emissions check.
quote: Originally posted by LS1-CAMARO: Thanks for the input, but i have a question....how can it be a cleaner and still crud up the injectors with soot?
The injectors stay clean, the soot forms in the combustion chamber. As long as you don't let it build up too much with over use of the toluene, the small amount produced will burn off.