
Difficulty in starting is due to the deposits and carbon buildup washed down by the fuel containing the additive accumulating at the bottleneck of the fuel system, causing partial blockage. Occasionally, black smoke may come out of the exhaust pipe, and the car body may shake. These phenomena indicate that the fuel additive is actually working, which is normal. After using 3-5 tanks of fuel containing the additive, these phenomena will gradually disappear. Some carbon deposits inside the engine have been cleaned. If the fuel injector gets clogged, it may lead to a decline in engine performance, causing unstable idle speed.


