The fundamental problem is the Motronik 2.4 engine managmemt system (EMS) for the BMW R1150RT is optimized to provide the lowest possible emissions and noise in the 3,000rpm to 4,000rpm range. This is accomplished by both retarding the ignition and running the engine in the leanest possible state. Not all bikes surge. Not all riders notice the surging. More than one factor can contribute to surging.

Even a good running bike will exhibit some surging. In the cruise zone (3,000rpm to 4,000rpm) the EMS will every several seconds make a change in the parameters trying to obtain optimal emissions. This will cause the engine speed to vary by 50 to 100rpm.

Key problem areas

1. Running the engine too lean. Many of the surging bikes also suffer from lean surge at cruise throttle positions.

2. Closed loop EMS control:
   1. Real-time adjustment. The EMS makes adjustments to the fuel mixture in the cruise range. The adjustments try and manage the air fuel mixture to be at the leanest possible setting (Lambda one)
   2. Heuristic injection map construction. The EMS continuously monitors the air fuel mixture and builds a modified base map based on the operational data that has been collected.

3. Bad Motronik 2.4 programming. Most of the surging could be cured by implementing software filters on the input sensors, and making mid-course correction in smaller increments.

4. Mismatched fuel injector nozzles. The manufacturing tolerances of the Bosch fuel injector nozzles can vary by up to 5%. This imbalance impacts performance and cause wider oscillations as optimal fuel mixtures are managed.

5. O2 (lambda) sensor placement. The O2 sensor is placed a long distance from the exhaust port and after the two exhaust pipes merge.

6. Parallel fuel injector firing. Both injectors fire at the same time. Fuel for the cylinder on its exhaust stroke sets in the intake port for one cycle until its intake cycle.

7. Retarded ignition advance curve. The ignition is retarded in the cruise zone to heat the exhaust system. This accelerates any lean mixture surge.

Possible Fixes

1. Fat Headers. The high performance Fat Headers for the BMW R1150RT and R1150RS slows the exhaust flow by increasing the diameter of the headers. These headers are an exact replica of the OEM but using 1.75 in. mild steel tubing instead of the 1.5 in. stock size. This slower exhaust speed allows the gases from both cylinders to mix better and give the O2 sensor a better average air: fuel reading. The additional HP and Torque reduce the effect of the corrections provided by the EMS.

2. Techlusion Fuel Injection TFi-1015 control box. This system is different in it's method of adjustment by dealing directly with the fuel injection signal after it leaves the factory ECU. It adjusts your fuel requirements without tricking sensors or modifying the factory settings which can limit the ECU's effectiveness at compensating for changing altitude or weather conditions.

3. Wunderlich (BBPower) tuning chip replacement - Not recommended

4. Matched fuel injector nozzles. As an experiment I had made a set of headers with two O2 sensor ports, positioned close to the exhaust ports. As we switched the O2 sensor from side to side a noticeable difference in smoothness and power. The injector nozzles were switched and the performance differences followed the nozzles. The injectors were replaced with a calibrated set with only 1.7% difference in fuel flow. The motorcycle still exhibited the imbalance in drivability.

   Conclusion: a) A very small difference in flow causes a noticeable difference in power. b) A correct solution would involve tuning the injector nozzle electrical signals.

5. Ideal solution is a field programmable EMS that would convert the fuel injection to sequential, and allow for different maps for each injector, field updateable injection maps and ignition advance curves.

Cat Code Plugs (CCP)

It is possable to change the EMS map selected by changing or removing the Cata Code Plug (CCP). The Pink CCP is the plug delivered on US spec bikes.

Pink CCP             P/N = 61368366-625   30-87-87a

Olive Green CCP  P/N = 61368366-621   30-86