Fundamentals of Fuel Injection

Mpfi Systems can either be : a) ‘Sequential’ i.e direct injection into individual cylinders against their suction strokes, or b) ‘Simultaneous’ i.e together

for all the four or whatever the number of cylinders, or c) ‘Group’ i.e into Cylinder-Pairs.

These techniques result not only in better ‘power balance’ amongst the cylinders but also in higher output from each one of them, along with faster throttle response.

Of these variants of Mpfi, 'Sequential' is the best from the above considerations of power balance/output.

‘Sefi’’, as advertised by Ford Ikon, stands for 'Sequential Electronic Fuel Injection', which technically is the best of the above variants of Mpfi. Hyundai/Maruti Mpfi systems are in fact Sefi too. Daewoo India had the (b) or (c) variants of above Mpfi systems on its Cielo/Matiz.

On the other hand, older Opel-Astra’s had a 'single point' fuel injection system, which is in between an Mpfi and the now obsolete Single-Carburettor systems.

The ‘Fuel Injectors’ are precision built ‘Solenoid Valves’, something like Washing Machine Water inlet Valves. These have either single or multiple ‘Orifices’ which ‘spray’ fuel into the Fuel inlet manifold of a Cylinder upon actuation, from a common Rail/Header pressurised to around 3 bar, fed by a high pressure electrically drive fuel pump inside the Petrol tank of the Car.

The ‘on-board’ ECU primarily controls the Ignition Timing and quantity of fuel to be injected. The latter is achieved by means of controlling the ‘duration’ for which the Injector solenoid valve coil is kept energized – popularly known as the ‘pulse-width’.

In general, an ECU in turn is controlled by the ‘data input’ from a set of ‘SENSORS’ located all over the Engine and its Auxiliaries. These detect the various ‘operating states’ of the Engine and the performance desired out of it. Such Sensors constantly monitor : 1) Ambient Temperature, 2) Engine Coolant Temp., 3) Exhaust/manifold temp., 4) Exhaust ‘O2’ content, 5) Inlet manifold vacuum, 6) Throttle position, 7) Engine rpm, 8) Vehicle road speed, 9) Crankshaft position, 10) Camshaft position, etc.

Based on a ‘programmed’ interpretation of all this input data, the ECU gives the various ‘commands’ to the Engine’s fuel intake and spark ignition timing systems, to deliver an overall satisfactory performance of the Engine from start to shut down, including ‘emission control’.

To get the best out of an Mpfi System, one should use – a) The OE recommended Petrol Additives or the new generation ‘Premium’ Petrol’s REGULARLY and b) NEVER Tamper with the OE Wiring Harness of the Car – EVEN to install the ubiquitous Music System OR any other Electrical Accessory - other than those ‘approved’ OE/Dealer and designed to suit the Car’s Wiring Harness/CWH ‘Couplers’.

‘BUCHERING’ OF THE OE-CWH IS AN ABSOLUTE TABOO FOR Mpfi CARS.