Spray Injectors

Spray Injectors

Spray Injectors – The most important feature of a GDI injector is not the flow rate of the injector but the fuel distribution and atomisation that form the injector’s spray pattern. ASNU has experience of GDI injectors with differences of up to 15% in flow rates between the best and the worst delivering injector, yet the engine still runs without a problem.

How is this possible? Developments in the Engine Management System now allow the flow rate to be automatically adjusted to an individual injector to compensate for any deficiency in the injector’s ability to deliver the correct amount of fuel. In theory this is ideal, in practice, it is not.

This feature is not correcting the problem, it is compensating for it and, although in the short term the vehicle is running fine, in the long term the problem will need to be addressed when the EMS reaches its compensation tolerance level and the engine’s check light comes on.

What are the symptoms of a fuel injector going bad?

As the injector’s performance deteriorates and the EMS compensates for the lack of flow, how does it measure and compensate for the changes and deficiencies in the fuel distribution and atomisation?

FACT 1:

If you had six injectors with six different deliveries, with the help of the EMS, the engine would run correctly. With six different spray patterns and six correct deliveries, the engine would run badly.

FACT 2:

If you had six injectors and six different spray patterns, the engine would run badly and the engine check light would illuminate. If not addressed, the EMS would eventually put the engine in ‘Limp Mode’ to protect it from damage.

FACT 3:
The injector’s spray pattern is designed for a very specific delivery angle and fuel droplet size. This ensures the fuel is directed to the correct location in the combustion chamber with a droplet size that will burn efficiently. Any disruption to the distribution or droplet size can and will have an adverse effect on the combustion process in that cylinder.

FACT 4:

The Fuel Trim Compensation for a bad spray pattern is to increase the fuel content. The engine’s EMS sees a weak
combustion stroke and believes that it needs more fuel. Usually, it has the correct quantity, it’s just not atomising
correctly. The cylinder now has excess fuel that is not only adding to the problem, but creating additional ones
in the process.

FACT 5:

Now the cylinder has excess fuel, this can cause carbon build-up on the piston, excess burning on the piston crown, bore wash, gumming, sticking and slow response of any gas recycling valves and components, lacquering of the lambda sensor as well as clogging and damage to the catalytic exhaust.