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Discussion Starter · #1 ·
hi.... i just got my 2002 998 from IL and the seller told me he added a fuel trimer to the bike ??? what is a fuel trimer ??? i see a small box with blinking small red lights .. what is the advantage of having fuel trimer??

Old Wizard
3,007 Posts
Fuel Trimmers

It's purpose is to allow the owner to make changes to the engine’s fuel delivery, needed often after modifications are made that affect the amount of air delivered to the engine at different rpm’s

Ducati’s engine management is provided by an open-loop fuel injection system that uses a computer to control the opening duration of its injectors based upon voltage levels presented to it from several sensors. The longer the injector is opened, the more fuel is supplied to the engine.

On earlier models, the computer contained a removable Eprom chip that stores a look-up table of injector durations for 16 throttle positions and 16 engine speeds. These chips can be removed and replaced with one re-programmed with different durations (fuel map) needed for fuel mixture changes necessitated by engine modifications. The fuel map supplied by Ducati is programmed to provide good fuel economy and to meet exhaust emission standards, so does not really provide optimum performance.

Your 998 uses the Weber-Marelli IAW 5.9M computer that unfortunately does not have a replaceable EPROM chip. However, there are after-market options available to modify the fuel map for engine, intake and exhaust system mods: Techlusion TFI box, Powercommander III, and the Ultimap U59 ECU.

The main problem here is that creating custom fuel maps is a big undertaking, and not to be taken lightly. It often requires many hours with a dyno and an expensive lambda exhaust gas analyzer to see real improvement over the Ducati baseline. Since most of us cannot afford the time or the special equipment it takes to do it right, the capabilities of a fuel trimmer is usually wasted. You need to be willing to spend the time (and money) it takes to get it done right.

For example, in the case of the Power Commander, if you have a Dynojet tuning center nearby, take it there first. The closer you can get initially, the better it will run. But getting it just right takes a lot more work, and experience.

Simply downloading a generic Dynojet map has obvious drawbacks. For one thing, there's a normal manufacturing variation between identical bikes, and second, there's going to be a variation between your bike and the mapped reference bike regarding cam timing, correct TPS setting, balanced throttle bodies, fuel pressure (fresh fuel filter) etc.

In general, Dynojet has a good product with the PC. Their centers use a closed loop tuning system, where the dyno controls the load, the PC reads the rpm/throttle and the lambda probe reads the mixture at each point. After you do a set of runs at each throttle position, the software (that reads and controls the dyno, PC and lambda) calculates a new map. You then repeat the process and refine the map. Each iteration gets it closer, giving your bike a custom map.
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