First and most obvious is the increase in fuel consumption. Carbon deposition is a gelatinous material that is highly absorbent, partially absorbing some of the fuel injected into the cylinder and increasing the resistance of some of the mechanical parts inside the piston and crankshaft. What's more, the fuel sucked up in this part will also form new carbon deposits in a state of incomplete combustion, a vicious cycle that will increase fuel consumption.
The second way to infer whether carbon has accumulated is that the car feels "dull" when accelerating or overtaking. No matter how we pedal, we can't give full play to the performance of the car, and sometimes we can hear abnormal noises coming from the engine, accompanied by a sense of frustration, which basically determines the accumulation of carbon, especially when overtaking.
The third phenomenon is also very obvious, when the engine has carbon accumulation, the engine idling speed is very unstable, the instrument panel pointer will also rise and fall, if the normal driving does not have too much impact, then it should also be the formation of carbon accumulation inside the engine.
Finally, the exhaust fumes are pungent, which may not be caused by carbon accumulation, because it may be caused by three-way catalytic converters. However, cars with high carbon accumulation are difficult to fully burn fuel, and the pungent smell comes from sulfur dioxide produced by incomplete combustion of fuel. With a professional cleaning agent cleaning three-way catalytic converter, it can be solved.