85 engine electrical.pdf - Vintage Snow

ENGINE ELECTRICALSystem III - Electronics OperationInput from the other sensors either adds to or subtracts a percentage from the pulse width to tailor the fuel/air ratiofor the specific altitude, air temperature and engine temperature. See illustration.)[J Leaner for warm airtemps, high altitude etc.././ "../ ........" ........]Richer for low altitude,cold engine, cold inletair, etc........ Pulse Width ZThrottle Position Y)The illustration below depicts pulse widths in milliseconds output by the ECU. Figure A shows a situation wherethe air temperature is low, the machine is at low altitude with a cold engine, wide open throttle and high RPM.The ECU determines the engine's fuel requirements and selects a relatively long pulse width which allows moreinjector open time for fuel to enter the engine.Figure AON r-----,IOFFLong Pulse Width (i.e. High RPM, Cold Temps., Low Altitude, etc.)Figure B ON nOFFn'-------'Short Pulse Width (i.e. Idling, Warm Temps., High Altitude, etc.))If the same engine were at high altitude on a warm day at low RPM and throttle settings, the ECU would select apulse width closer to Figure B, indicating a shorter injector open time and less fuel entering the engine. In this waythe system can ultimately vary the mixture for all temperatures, loads and altitudes by varying the amount of timethe injectors are open per revolution.8/94 4.50