Fuel, Emission Control and Alternative Fuel Systems
Fuel and combustion
This domain tests petrol and diesel fuel systems, emission controls and alternative fuels. Petrol engines use port or direct injection; diesel uses high-pressure common rail or pump systems. Fuel pressure, injector spray pattern, air filter restriction and lambda feedback affect mixture. The lambda sensor switches around 0.45 V; a steady 0.1–0.3 V suggests lean, 0.6–0.9 V suggests rich. Catalytic converters need correct mixture; leaded fuel and excessive oil burning damage them. EGR reduces NOx, PCV controls crankcase gases, and EVAP prevents fuel vapour escape.
Diesel after-treatment and alternatives
BS-VI diesel vehicles use DPF and SCR with AdBlue. Use low-ash engine oil and the specified AdBlue; contaminated fluid causes derate. DPF regeneration needs the right driving cycle or a scan-tool procedure. CNG and LPG need leak checks, approved cylinders and hydro testing. Electric and hybrid vehicles need high-voltage safety, not fuel-system habits. Ethanol-blended petrol is compatible only as the maker allows.
Worked example
A petrol car has a lambda sensor stuck near 0.9 V and long-term fuel trim at −20%. Rich command means the ECU is removing fuel. Check for a leaking injector, high fuel pressure, restricted air filter or a faulty coolant sensor telling the ECU the engine is cold. Do not condemn the sensor until the mixture cause is found.
Traps
Do not use leaded petrol or wrong AdBlue, ignore DPF warning lamps, or test CNG leaks with a flame. A P0420 catalyst code may be caused by an exhaust leak or rich mixture, not a failed converter.