Foreword

Foreword

Because the IAW 08F.5T MPI system fitted to the 1242 engine uses the same operating strategies and components as the SPI systems fitted to the 1108 and 1242 engines, it is similar to those systems in many respects. This chapter will therefore discuss only the essential differences between the two systems. For further information, consult the previous chapter «S.P.I. fuel system 1108-1242»

The I.A.W. 08F.5T system fitted to the Punto 1242 engine is an integrated digital electronic ignition system with solid-state advance and timing and electronic intermittent, multipoint, non-phased petrol injection. When all injectors are connected in parallel in a system (FULL-GROUP), and inject simultaneously upon each turn of the crankshaft half of the amount of fuel necessary for forming the air-fuel mixture, the mixture is said to be intermittent, multiple, non-phased.

The Weber-Marelli I.A.W. 08F.5T injection-ignition system uses a direct measurement system known as «SPEED DENSITY - LAMBDA».

• in practice this system uses ENGINE SPEED (revs per minute) and AIR DENSITY (pressure and temperature) to measure the amount of air taken in by the engine.
  The amount of air taken in by each cylinder upon each engine stroke depends on intake air density and also on standard displacement and volumentric efficiency.
• Air density is taken to be the density of air taken in by the engine and calculated as a function of absolute pressure and temperature - both measured in the inlet manifold.
• Volumetric efficiency is a parameter relating to the cylinder filling coefficient. It is calculated on the basis of experimental tests carried out on the engine throughout its range of operation and then memorized in the ECU.
  Once the amount of air taken in has been established, the system must provide sufficient fuel to make up the required fuel mixture concentration.
• The information required for calculating the concentration (air-petrol) required for adhering as closely as possible to a stoichiometric ratio is obtained by sensors and converted to electrical signals.

The system is able to measure instantaneously:

1. Number of revs and relative position of pistons in relation to TDC
2. Instantaneous absolute pressure in the inlet manifold.
3. Accelerator throttle aperture.
4. Coolant temperature.
5. Inlet manifold air temperature.
6. Lambda probe signal or counter-check on concentration.