Fuel supply, injection and emission control systems
Fuel supply, injection and emission control systems
This domain covers petrol and diesel fuel delivery, air-fuel metering, and the emission hardware fitted to BS-VI vehicles.
Core rules
- Petrol MPFI: the pump supplies about 3–4 bar; injector resistance is typically 12–16 Ω; pulse width is the command. Never measure injector resistance with the ECU connected.
- Diesel common rail: a low-pressure lift pump feeds a high-pressure pump; rail pressure can exceed 1,800 bar. Never crack a high-pressure line by hand; use a gauge and follow depressurisation.
- Closed-loop petrol uses an upstream O2 or lambda sensor; P0171 means lean, with short-term fuel trim usually above +10%. Look for unmetered air before blaming the pump.
- BS-VI diesel: DOC, DPF, SCR with AdBlue, and EGR. DPF regeneration needs exhaust temperature; short trips cause soot loading.
- OBD-II monitors include catalyst, EVAP, O2 and misfire. Read freeze frame before clearing.
Worked example
A car idles rough with P0171, STFT +18% and LTFT +12%. Propane enrichment makes trims fall toward zero. That proves the ECU can add fuel and the problem is a vacuum leak, not a weak pump. Smoke-test the intake and find a split PCV hose. If trims stayed positive with propane, low fuel pressure or a restricted injector would be suspect.
Traps
- Clearing codes first, erasing freeze frame and readiness.
- Using a test lamp across an injector driver.
- Assuming P0420 always means a dead catalytic converter; exhaust leaks and O2 response must be checked.
- Filling AdBlue into the diesel tank.