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     OS 140 RX-FI    

The electronic fuel injected version of the trusty old 140RX.  The big change is a totally new fuel system where the rear-cover mounted fuel-pump is removed as is the needle valve. Now the tank is pressurized through a check-valve from the engine crankcase.  The pressurized fuel is fed to a electronically controlled injector. The injector is controlled from a ECU (Electronic Control Unit) that receives three signals :

  1. The same signal as is supplied to the throttle servo. This is similar to the throttle position sensor that is present at most (if not all) injection systems used in modern cars.  For this reason it is very important to set up the throttle linkage according to the manual. During setup the high and low positions (pulse-lengths) are stored into the ECU. It's important to update these settings if the engine is taken out of the model and the put back in.

  2. A RPM-signal generated from a sensor located in the rear-cover of the engine.

  3. A temperature signal from a sensor besides the exhaust-port of the engine.

The amount of fuel that the ECU supplies to the engine is dependant of the signals described above. In addition the user can set the base-values individually at three throttle settings :

Idle : This setting can only be set manually through the menu on the ECU.

Midrange : With the ECU set in 'Fine' mode the midrange mixture can be set to ±100% (of whatever) from a AUX-channel on the transmitter.  The setting is adjusted when the throttle stick is in center, and stored into the ECU when throttle stick is moved back to idle.

Full power : As with midrange adjustment with the obvious difference that the adjustment is done with the throttle stick in the full-power position.

When the ECU is set into 'ATL'-mode the same AUX-channel on transmitter can be used to adjust the fuel mixture linear over the range from idle to full.  This works more or less as the 'meetering' function used in past years.  

Practical hints :

  • The engine is easy to start by hand when it's properly primed and the tank is pressurized.  Pressurizing an priming is easiest done with an electric starter.

  • I have found it easiest to have the ECU in 'ATL'-mode for normal operation. When there is a need for midrange adjustment I switch it to 'Fine' and make a small adjustment while on ground.  I set the ECU back to 'ATL' befory commencing flying.

22 April 2003 : One of the engines is mounted into my rebuild Alliance and flown quite a bit during Easter.  The improvement over the normal 140RX is definite.  Both with respect to throttle-responce and power.  I believe the improved power is related to a more stable and accurate fuel supply, and the fact that the engine can be ran leaner due to the temperature sensor that is an input to the ECU.  

2. March 2003: Made some bench-testing today, excellent.  This engine really runs very well, low and stable idle (down to 11-1200 RPM) excellent transition and good power.  The ECU showed a healthy 7550 during the first run, with the normal (for me) Greve muffler and APC 17x13.  I just followed the instructions letter by letter during setup, and it seemed to end up correctly.