Abstract: Injector cleaning/testing apparatus is arranged to enable electrically actuated injectors to be cleaned and tested while in situ on an engine. The apparatus is connected to the fuel supply system of the engine which feeds fuel and/or cleaning fluid to the engine injectors. Measuring means is also provided for measuring the rate of flow of fuel through the injectors. Fuel is pumped to pressurize the supply of fuel to the injectors; the pressure is measured and the rate of change of the pressure is determined as an injector is opened thereby determining the rate of flow through the injector. The apparatus also includes an arrangement whereby the engine fuel supply pump is used during cleaning and an arrangement by which the injectors may be actuated in different modes without disconnection.