Advance Auto Parts offers the Chevron Techron 20-oz. Fuel System Cleaner, model no. 65740, for $7.88. (Amazon charges the same with free shipping for its Prime members.) Opt for in-store pickup to avoid the $9.99 shipping fee. That's $13 under the lowest total price we could find for a shipped bottle, although it was a buck less last summer. It's designed for carbureted or fuel-injected spark ignition engines.