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Tuning + optimization of Buell



It goes without saying that proper fuel delivery is critical for all engines.  Making sure your engine is being fed properly should be part of a routine maintenance check, before any form of tuning is done and when diagnosing an EFI related issue.  Buell motorcycles are notorious for having fuel system problems, which are often undetected or misdiagnosed.  As these bikes age the fuel pump assemblies can develop leaks that cause a loss of fuel pressure.  More often than not, the owner is unaware of a problem because by default, the ECM will try to compensate for this issue by raising the Adaptive Fuel Value (AFV) by as much as 150% which increases the duration of the injector pulse.  With a high AFV, the injectors are capable of delivering enough fuel at lower RPMs and cruising speeds, but at higher RPMs the injectors are eventually "maxed out".  The result is a very dangerous lean condition that goes undetected by the O2 sensor since high RPMs and throttle angles are outside of the closed loop range of the fuel mapping.  Instead of getting a Check Engine Light at an early stage of the problem, the owner may not be aware of the situation until something catastrophic happens.  


Even if your bike seems to be running well it's a good idea to look at what the current AFV setting is.  A tutorial for this is found HERE.  An AFV above about 108 near sea level could be caused by low fuel pressure, intake leak, sensor issue, etc.  If you see an AFV of 120 or more, it's almost guaranteed to be a fuel delivery problem.


If you suspect a fuel system problem you should measure your fuel pressure. For XB models we now offer a Fuel Pressure Tester.  This plugs in to the quick disconnect fitting of your fuel line once it is disconnected from the throttle body.  You can then perform a Fuel Pump Test using the Ecmdroid application.  On X1 and S3 models the pressure is measured at the Schrader valve located under the tank at the fuel outlet fitting.  The measured pressure should be ~49 PSI. This pressure should also bleed off slowly after the pump turns off.