Re: 03 yammy 4 stroke running bad again.
then odds are its a problem not monitored by the ECU.<br /> if ya wanna watch the timing and ISC work then while its on the laptop disconnect the intake air sensor or the coolant sensor and watch the ISC values, if they move and engine speed does not increase look closly at the ISC.<br /> this motor will pretty much trouble shoot itself if you let it.<br /> like I say any sensor failure will result in an idle speed of about 900 RPM. pulser failure will result in fixed injection and ign timing will fix at 10*BTDC regardless of gear position. <br /> so if the problem was actually a failed pulser or an open or shorted coolant,intake air temp or intake pressure sensor the ISC would opento a default setting of 900 RPM. if the TPS is unplugged or fails ign and fuel control will be done by intake air pressure sensor and the ISC will default to the 900 RPM setting and idle speed may increase. thats when the laptop is nice, you can watch what the ECU"ses" and how it reacts and make a physical comparison.<br />the ECU gets RPM and crank positon information from the pulser coils, it gets throttle angle information from the TPS, it gets engine load information from the intake pressure(MAP) sensor, the engine cooling sesnor and the intake air temp sensors fine tune fuel delivery for varying air densities and block temps.<br />The ECU is actually rather stupid, it takes vltage signals input to it to make an output according to an internal truth table.(map) if inputs a,b and C are value E then the outputs of x,y and Z are modified accordingly.<br />its all about keeping a 14/1 air/fuel mix in the combustion chamber and sparking it at the correct time.<br />the ECU does not monitor actual fuel flow through the injector nor fuel rail pressure, it assumes all is ok if the high pressure pump is running.<br /> based on input information about engine speed,throttle opening,intake air pressure(vacum) intake air temp and block temp the ECU will control the "on" time of the injector and where the piston is when spark occurs.<br /> just like engines of the 1800's, its all about suck,squeeze, bang and blow. all that other stuff just helps it go.
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