NHTSA Preliminary Evaluation PE06001

THIS INVESTIGATION WAS OPENED BASED ON SIX ALLEGATIONS OF MOTOR COACH AND BUS FIRES ALLEGEDLY CAUSED BY THE ENGINE?S TURBOCHARGER.DURING THE INVESTIGATION, DETROIT INFORMED ODI THAT TURBOCHARGER SPEEDS WERE INCREASING (SINCE YEAR 2000) TO OPTIMIZE EMISSIONS.(THEORETICALLY, HIGHER TURBOCHARGER SPEED INCREASES AIR SUPPLY INTO THE ENGINE AND, IN CONJUNCTION WITH AN OPTIMUM FUEL CURVE, INCREASES POWER AND REDUCES EMISSIONS.)THESE INCREASED SPEEDS RESULTED IN TURBOCHARGER COMPRESSOR WHEEL FAILURES.THE COMPRESSOR WHEEL FAILS DUE TO LOW CYCLE FATIGUE AS THE RESULT OF CERTAIN DUTY CYCLES.THE FAILURE RESULTS IN LUBRICATING OIL PASSING INTO THE EXHAUST SYSTEM, RESULTING IN SMOKE AND POSSIBLY A FIRE.TWO DIFFERENT TURBOCHARGERS ARE INVOLVED, MANUFACTURED BY HONEYWELL AND BORG WARNER.DETROIT'S REMEDY IS TO RECALIBRATE THE ECM TO DETECT A REDUCTION IN TURBOCHARGER OUTPUT CAUSED BY A WHEEL FAILURE.UPON DETECTION THE NEW LOGIC WILL THEN REDUCE FUEL TO THE ENGINE AND SHUT IT DOWN TO PREVENT A FIRE.THE DRIVER WILL HAVE AN OVERRIDE BUTTON WHICH WILL ALLOW THE VEHICLE TO BE LIMPED TO A SAFE LOCATION.SOME MODELS MAY REQUIRE A BAROMETRIC PRESSURE SENSOR TO BE INSTALLED ON THE OUTPUT SIDE OF THE TURBROCHARGER THAT WILL SIGNAL THE ECM WHEN OUTPUT PRESSURE DROPS, TEMPORARILY SHUTTING DOWN THE ENGINE.THE RECALL ACTION TAKEN BY DETROIT RESOLVES THE ISSUES RAISED BY THIS INVESTIGATION.THIS INVESTIGATION IS CLOSED.