In the seventies when fuel consumption gained more importance Sulzer introduced the so called Variable Injection Timing and Fuel Quality Setting (VIT and FQS) system on its low speed two stroke engines. The VIT and FQS system performs two main tasks. The VIT part is an automatic function that controls the injection begin depending on the actual engine load and cares for optimum part load fuel consumption. The FQS part is a manual adjustment that is meant to be used to match the injection timing to the quality of fuel used. VIT and FQS have been introduced as standard on RTA engines at first in a mechanical and later in an electronic version. The latter is the only standard system for current RTA engines and will be the main subject of this Bulletin. A retarded injection is one of the measures used on Sulzer RTA engines to comply with the International Maritime Organization (IMO) NOx emission regulations. The applied injection delay depends on engine type and rating and has been introduced in the DENIS-system as a new, load-independent parameter. Therefore the VIT system has gained considerable importance with the introduction of the engine tuning complying with the IMO NOx (Oxides of nitrogen) emission regulations on the Sulzer RTA engines. Due to the optimization character of the VIT function an engine can run both with and without VIT and FQS function without any loss of operability. However, because of its proven beneficial effect on fuel consumption especially at part load it Is advisable to have the VITand FQS system always working during normal engine operation. All RTA engines have been designed for continuous VIT and FQS operation i.e. the use of VIT and FQS keeps the engine parameters well within safe limits. On the latest RTA engine designs complying with the IMO NOx emission regulations, the range of FQS adjustment is limited so that NOx emission limits are ensured with any setting of the FQS. This Service Bulletin shall explain the VIT and FQS system in its different design versions and give some general advice on how to check the system and its correct function in order to guarantee maximum availability and thus benefit for the operators.