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Rotax 914 boost problem

Posted By:
Rene Vercruyssen
#1 Posted: 6/1/2010 17:11:47

Who is the recognized authority on the turbocharged Rotax 914?  My hanger neighbor just bought a very nice Europa with a 914 and it occasionally limits its boost to as low as 25 inches.  The ECU was recently replaced as it was the suspected culprit, but the occasional problem still presents itself with no discernable pattern.  Who can we turn to for sound advice?

Thank you in advance,


EAA #858265


World's largest RV-4 Driver (6' 1", 330 lbs)

Greg Dougan
#2 Posted: 6/3/2010 19:37:30

No Rotax time but several thousand hours in other makes. I would check for:

  • fuel control problem - getting way rich
  • hanging wastegate - try mouse milk
  • air leak in the induction system. - loose hose clamp or cracked pipe


Peter DuFresne
#3 Posted: 6/8/2010 00:21:55

I built a Sky Arrow in 2002 with a Rotax 914UL.  To date I have over 600 hours of experience with this engine.  I have also had problems with under-boost.  At times the boost at full throttle was being limited to about 35".  By using spray contact cleaner on the sensor connectors I was able to restore 40" at takeoff.  I assume that the ECU was receiving an incorrect airbox temp reading due to high resistance in the connector.  The ECU will limit boost if it senses high airbox temp.  The other problem was with the wastegate.  It would cause odd manifold pressures, and the red over-boost warning light would come on during cruise.  After much searching I found that the wastegate valve disc was hanging up on the edge of the valve bore.  The disc is attached to a lever arm with a high temperature rivet.  There is some play to permit the disc to seal over the bore when closed.  Unfortunately, mine had too much play which allowed it to hang up at times and not fully close.  After two failed attempts to fix it, I finally had the disc welded to the arm.  That fixed the problem.  I have had no further boost problems since then.  To prevent future problems I clean the sensor contacts as part of the annual condition inspection.

I hope this helps.


EAA #262380