Fitting spark plugs to a GDI engine

Posted on May 10th, 2019 by Rob Marshall

Fitting spark plugs to a GDI engine

While many of us leave car maintenance to garages, many owners are technically-interested in what goes on beneath their bonnets, even if they choose not to join the rising number of DIYers who like to get their hands dirty.

The humble spark plug is one of the most critical of car components, yet is one of the simplest parts to fit. Using a suitable socket, a typical spark plug is unscrewed and discarded, before another one is fitted in its place.

However, as modern engines have become more precise, you need to take extra care with direct injection (GDI) units. These have fuel injectors positioned within the engine cylinder, rather than behind the inlet valve. In these cases, the spark plug’s side electrode’s position in relation to the fuel injector is relevant to ensure optimum combustion efficiency and low exhaust emissions. Failure to neither tighten the spark plug to its specified tightness (torque), nor angle setting, can cause an engine management light to come on, which is an MOT failure.

Additionally, you should not use any lubricant on the speak plug threads, because this alters the torque value, risking not only the incorrect spark plug electrode position but also overtightening. As most modern GDI engines require more expensive spark plugs, which utilise precious metal platinum and iridium alloys in their construction, never downgrade to a cheaper spark plug. As with all car ignition components, buy plugs that are made by established brands through trusted suppliers. Do not risk potential fakes/low grade replacements via unknown sellers on online market places.