Boat Diesel – Injectors

Injectors work like a relief valve. The internal piston is spring loaded, remaining closed as pressure builds and opening when the set pressure (break setting) is reached. Fuel then squirts in very fine jets into the engine through several tiny holes in the end of the injector.

The spring ensures that the opening and closing times are very precise. The precise amount of fuel required, as determined by the fuel pump speed control setting, will enter the combustion chamber. The injector itself does not control the amount of fuel. It just opens and allows through the amount being pumped into it.

Some injectors can be serviced, others are throwaway items. They can, however, last a considerable time – over 1,000 running hours if serviced properly. Always follow the maker’s service recommendations.

Multi-hole injector
1 Nozzle holder. 2 Nozzle nut. 3 Spindle. 4 Spring. 5 Upper spring plate. 6 Spring cap nut. 7 Cap nut. 8, 9, 10 Joint washers. 11 Inlet adaptor. 12 Leak-off connection. 13 Banjo bolt. 14 Nozzle. 15 Needle valve. 16 Spray holes.

It is possible to take an injector out and then turn the engine over to check if fuel is being squirted through it. But we do not advise it. WARNING. Fuel jets, under enormous pressure, will easily penetrate the skin, or blind an eye. The fuel is also highly toxic.

The pockets in which the injectors sit are often sleeved, and the end of the injector is always sealed against the cylinder head to stop air and combustion gases leaking past. It is wise to remove the injectors, whether or not they need servicing, every few years to clean the sleeves, and ensure that they are not seized in by rust. Don’t drop any debris into the engine, and refit with new sealing washers, if fitted.

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