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CONTINUED –S&S® VARIABLE FUEL INJECTION (VFI) MODULESOLD MODULE? NEW MODULE?IT’S ALL GOOD!S&S VFI with closed loop capabilty is not a separate or entirelydifferent product from the original VFI system. Closed loopcapability is really just a very powerful and useful new feature,programmed into all current production S&S VFI modules.Existing S&S modules can be easily updated with the currentECU operating software to achieve closed loop capability. Newor updated modules can be operated in the closed loop modeprovided oxygen sensors are available. It’s a simple matter ofinstalling the S&S VFI Closed Loop Sensor Kit and enabling“closed loop tuning” within the ProTune II software.S&S VFI modules can still be operated in open loop modeif there are no oxygen sensors in the system. This is useful instock replacement applications, but for the minimal additionalcost, closed loop is the way to go. S&S VFI modules still evaluatedata from the five standard sensors: crank position, MAP, throttleposition, air temperature, and cylinder head temperature, andthey still require a base map in order to run. The difference isin how the module is able to use the additional informationprovided by the oxygen sensors to continuously optimize theperformance of the engine. When operated in the closed loopmode, S&S VFI becomes an adaptive system. It adjusts in realtime by sensing the level of the oxygen in the exhaust gases andautomatically correcting fuel delivery to maintain the optimumfuel/air mixture over a wide range of operating conditions.Closed loop VFI can even compensate for minor modificationsto the engine configuration automatically. More extensivemodifications that change the power output of the engine bymore than about 20% require a new base map.Pictured: S&S VFI Closed Loop Sensor KitThe S&S VFI Closed Loop Sensor Kit allows VFI users to upgrade to a closed loopsystem. The kit includes two oxygen sensors, two weld-in exhaust bosses, anoxygen sensor wiring sub-harness, all required connectors, and instructions.Kit shown is for Delphi® style S&S module. The new kit for Magneti Marelli® styleS&S module is similar, but with a slightly different wiring sub-harness.S&S VFI CLOSED LOOP SENSOR KIT INSTALLATIONInstalling an S&S VFI Closed Loop Sensor Kit consists of mountingthe weld-in bosses in the exhaust pipes, and installing the oxygensensors and wiring sub-harness. A boss and oxygen sensor mustbe installed in each exhaust pipe since the system tunes eachcylinder independently. Installation of the oxygen sensors on theback or underside of the pipes makes them unobtrusive in nearlyall applications. The wiring sub-harness installation requires minorwiring harness modifications. Complete installation instructionsare included.HOW DOES THES&S CLOSED LOOP VFI SYSTEM WORK?The module starts with a base fuel map, and makes adjustmentsbased on feedback from the oxygen sensors. S&S supplies basemaps for several displacement groups, which can be used asa starting point to get a bike up and running. The S&S closedloop system then tailors the map to the specific requirements ofyour engine, while you ride. Fuel map changes are temporarilystored in the cylinder offset files, and can be made permanentby using the “map merge” function of the ProTune II software. Inthis way the corrections that the module has “learned” become apermanent part of the tune file, and can be used as a base mapor starting point if further performance modifications are made.Closed Loop VFI can automatically compensate forthe following modifications as long as the change inhorsepower output is less than about 20%.▼ Displacement▼ Cam change*▼ Exhaust change*▼ Head porting or aftermarket heads▼ Gear ratio* It should be noted that the cam and exhaust system must beappropriate for the displacement, compression ratio, and intendeduse of the engine. No amount of tuning will entirely correct for apoor cam and exhaust choice.32 Variable Fuel InjectionEmail us at sscust@sscycle.com