My Toyota RAV4 with a D4 engine has difficult starts, engine suddenly stops, weak acceleration and high fuel consumption. My mechanic says the engine valves and fuel injectors are caked with a carbon material. What is the cause of the carbon and how can I prevent it?
Deposits (particles) in a petrol engine result mainly from the combustion (burning) of fuel and air in vehicle cylinders. When fuel is burnt in the engine most of the chemical reaction products will go back to the air intake system. These deposits will accumulate in the intake manifolds and on the intake valves preventing free inflow of air to facilitate burning of fuel in the combustion area.
The spongy deposits also absorb some of the fuel before it is delivered to the combustion chamber. This situation prevents instant engine ignition, causes erratic idling, poor acceleration or engine stalling and increased fuel consumption as the engine computer attempts to make up for the energy (fuel) loss by delivering more fuel. Automotive engineers and fuel scientists have noted that the tolerance of deposits in petrol (gasoline) engines has greatly reduced since the transition from carburretor to electronic fuel injection (EFI).
The most outstanding being multipoint and the more recent charged (pressurised) direct fuel injection (D4 in Toyota or GDI in Mitsubishi). The engines with these fuel systems built since the 1990s greatly rely on unrestricted air intake to achieve efficient burning.
Shell Fuel scientists have developed and formulated the differentiated Shell Fuel Save Unleaded which has detergent chemicals that prevent deposit build up on the engine intake valves and substantially stops the above energy (fuel) loss.