Location, location, location

 In a GDI engine, the fuel injector in each cylinder is moved from behind the intake valve into the combustion chamber. With petrol being sprayed into the cylinder at the hottest point – and more accurately, in relation to the spark plug position – more complete combustion results. GDI engines tend to run leaner in certain situations – at a air/fuel mix of around 40:1 as opposed to 14.7:1 – but this introduces a NOX pollution issue that must be resolved (see our Exhaust gas

recirculation valves feature on page 6). Component supplier, Bosch, states that GDI fuel economy is improved by around 15% and low-end torque by up to 50%.

Unfortunately, relocating the injectors creates a number of issues, due mostly to them being exposed fully to the combustion process, instead of being protected by the closed intake valves found on earlier port-injection designs. Due partly to the increased presence of soot, the injector nozzles can become fouled, not helped by their precision multi-hole nozzles being smaller than before. This contamination affects accuracy of the vitally important fuel spray pattern, reducing efficiency and causing running problems. The injectors can also suffer from lacquering, one reason for which is an increased amount of bio-ethanol in petrol that affects fuel flow through the injector nozzles.

The main way to resolve injector issues is to use a quality fuel additive not only as a repair, but also as a preventive measure. During servicing, assess live data information about fuel injector flow, including any corrections that the ECU has to make that could identify a potentially contaminated injector. When replacing spark plugs, be aware that the electrodes’ positions, relative to the injectors, are crucial; heed any torque/angle settings.