Know your MPFi Car Systems

Ever since the first single-cylinder petrol engine driven Car appeared on the roads during late 19th century, a ‘Carburettor’ became synonymous with it. Later on with the advent of multi-cylinder Engines, so did the ‘Distributor’ or ‘Delco’s.

During the last Century, both evolved considerably – till the ‘Euro-II’ like Pollution Norms got the better of them. For, the Carbs worked on a fundamental principle of ‘reaction’, which could easily get stifled for many reasons. Whereas man, wanted to be literally in the Driver’s Seat – as always.

And thus, as the cliché of necessity being the mother of invention goes, a System of ‘controlled-feeding’ of Fuel + Air + Ignition Spark to the ICE Cylinders in the early ‘80s evolved. A ‘system’ like that had to be based on the engine’s ‘needs of the moment’, such as the load on it, its rpm, vehicle’s road speed etc.

Such a ‘system’ had to ensure that the ‘ob-Nox-ious’ Pollutants were kept to a bare minimum all over it’s operating range – not to mention squeezing the maximum ‘mileage’ out of the last drop of fuel that went into it. Thus ‘fuel-injection’ systems were born – replacing nearly a century old Carburettors.

For the uninitiated, ‘MPFi’ stands for ‘Multi point fuel injection’. Such a system ‘injects’ fuel into individual cylinders, based on commands from the ‘on board engine management system’ Computer – popularly known as the Engine Control Unit or the ECU.

MPFi Systems can either be: a) ‘Sequential’ i.e. direct injection into individual cylinders against their suction strokes, or b) ‘Simultaneous’ i.e. together or 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, 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. The erstwhile Cielo’s and Matiz’s had the (b) or (c) variants of above MPFi systems.

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 driven 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 Air 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’.

This/Part-1 of a 4-part Article is an attempt to familiarise the average ‘BS-II/III’ Car Owner as to what actually lies beneath their Bonnets. In Part-2, we’ll talk about the do’s and don’ts relating to MPFi Cars. In Part-3, for the more curious ones, we’ll see how the stuff works and in Part-4, we’ll explore the commonly encountered problems and DIY-Trouble Shooting.

Immediately, to get the best out of an MPFi System, one should always use – a) The OE recommended Petrol Additives with the ‘Regular’ Unleaded or the new generation ‘Premium’ Petrol’s 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’ by the OEM/Dealer and ‘installed’ by him, as these are designed to suit the Car’s OE Central Wiring Harness ‘Couplers’ provided for the purpose. ‘BUTCHERING’ OF THE OE-CWH IS AN ABSOLUTE TABOO FOR MPFI CARS.

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