--- title: "EFI, MPFI and diesel injection pump" subject: "Internal Combustion Engines" chapter: 4 key: "semester_6/internal_combustion_engines:efi-mpfi-fuel-pump-injection-systems" source: https://www.bctengineer.com/q/semester_6/internal_combustion_engines/efi-mpfi-fuel-pump-injection-systems site: BCT Engineering --- # EFI, MPFI and diesel injection pump Internal Combustion Engines · Chapter 4: Carburetor & Fuel Injection systems - Asked in: year not given, 4+4 marks - Video: [Basics of M.P.F.I System](https://www.youtube.com/watch?v=oWQuNZeEAo8) — Automotive Crux - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/internal_combustion_engines/efi-mpfi-fuel-pump-injection-systems - Whole chapter: https://www.bctengineer.com/md/semester_6/internal_combustion_engines/chapter-4 ## Question Explain the working of a multi-point electronic fuel injection (MPFI) system of a petrol engine with its main components. State its advantages over a carburettor. Describe briefly the fuel feed pump and the jerk-type fuel injection pump used in diesel engines. ## Short answer In an MPFI system, an injector per cylinder near the intake valve is controlled by an ECU using sensor inputs to inject precise fuel. It offers better fuel distribution, higher power, lower emissions and good cold starting over a carburettor. The diesel feed pump supplies low-pressure fuel to the jerk-type injection pump, where a cam-driven plunger pressurises fuel and a helical groove controls injected quantity by varying effective stroke. ## Answer #### MPFI system In MPFI one injector is fitted in the inlet manifold near the inlet valve of each cylinder. An electronic control unit (ECU) decides how much fuel is injected. ```text Sensors --> [ ECU ] --> Injectors (one per cyl.) MAP/MAF, | ^ throttle, ignition fuel rail <- pump <- tank coolant T, timing + pressure regulator O2, rpm ``` **Components** - Electric fuel pump, filter, fuel rail with pressure regulator (about 2.5-3 bar). - Solenoid injectors, opened for a short pulse width set by the ECU. - Sensors: air-flow or manifold pressure, throttle position, engine speed and crank position, coolant temperature, intake air temperature and exhaust oxygen (lambda) sensor. - ECU with stored maps. **Working:** the ECU uses the sensor data to calculate the air mass, and opens each injector for the time needed to give the required air-fuel ratio (about 14.7:1 with a three-way catalyst, using the lambda sensor as feedback). Injection may be sequential, timed with the inlet valve. **Advantages over a carburettor** - Accurate mixture to every cylinder, better distribution. - Higher volumetric efficiency, since there is no venturi restriction; more power. - Better fuel economy and lower emissions; works with catalytic converters. - Better cold starting and throttle response, no icing. #### Fuel feed pump A low-pressure diaphragm or plunger pump driven by a cam lifts diesel from the tank, passes it through filters, and supplies it to the injection pump at about 1-2 bar. #### Jerk-type injection pump A plunger moves in a barrel with an inlet port and a spill port. The cam lifts the plunger. After the plunger covers the ports it raises the pressure of the trapped fuel to 150-300 bar or more, which opens the delivery valve and injector (the "jerk"). A helical groove on the plunger uncovers the spill port, the pressure collapses and injection stops. Rotating the plunger changes the effective stroke and therefore the quantity of fuel injected for each load. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Where are the injectors in MPFI? A. One per cylinder in the inlet manifold near the inlet valve B. One in the throttle body C. Inside the combustion chamber only D. In the fuel tank Answer: A. Each cylinder gets its own injector, giving better mixture distribution. (Key point: MPFI layout) 2. How does the ECU set the fuel quantity? A. By the venturi size B. By the injector pulse width, based on sensor data and lambda feedback C. By the float level D. By the spill port Answer: B. The ECU calculates air mass and opens each injector for the needed time to hold about 14.7:1. (Key point: Fuel quantity control) 3. Why is volumetric efficiency higher with MPFI than a carburettor? A. It uses a bigger cylinder B. It uses a higher compression ratio C. There is no venturi restriction in the intake D. Fuel is heated Answer: C. Removing the venturi reduces flow restriction, giving more power. (Key point: MPFI advantage) 4. How does the jerk-type pump change the fuel quantity? A. Changing cam speed B. Changing the delivery valve C. Changing barrel size D. Rotating the plunger changes the point the helical groove uncovers the spill port Answer: D. Rotation changes the effective stroke, so injection stops sooner or later and delivery varies with load. (Key point: Jerk pump metering) ## Related in Internal Combustion Engines - [IP, BP and efficiencies of a petrol engine](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Aindicated-brake-power-efficiency-numerical) — Internal Combustion Engines, chapter 8 - [Four-stroke SI engine working and components](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Afour-stroke-si-engine-working-components) — Internal Combustion Engines, chapter 2 - [Heat balance sheet of a diesel engine](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Adiesel-engine-heat-balance-numerical) — Internal Combustion Engines, chapter 8 - [Jet diameter of a simple carburettor](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Asimple-carburettor-jet-size-numerical) — Internal Combustion Engines, chapter 4 - [Efficiency ratio and specific fuel consumption](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Arelative-efficiency-sfc-numerical) — Internal Combustion Engines, chapter 8 - [Simple carburettor and its limitations](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Asimple-carburettor-working-compensation) — Internal Combustion Engines, chapter 4 ## Related in other subjects - [Carburettor vs injection; TBI, MPFI, GDI](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Acarburettor-vs-fuel-injection-systems) — Automotive Technology, chapter 2 - [Diesel plant components and fuel supply](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Adiesel-components-fuel-supply) — Power Plant Equipment, chapter 5, asked 3× - [Diesel engine 75 kW: fuel consumption and efficiencies](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Adiesel-75kw-fuel-consumption) — Power Plant Equipment, chapter 5 - [Fuel supply system of diesel plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Adiesel-fuel-supply) — Power Plant Equipment, chapter 5, asked 3×