two-spring injection-nozzle with needle-displacement sensor low fuel injection (the valve needle is lifted against the weak spring # 1) high fuel injection (the valve needle is lifted against stiff spring # 2) the needle-displacement sensor senses start of injection description ordernumber 291 see also: Common Rail Piezo-injector high-pressure fuel pump TSI (FSI) L-Jetronic fuel injection distributor pump (adjusting the injection timing advance)