Re: 03 yammy 4 stroke running bad again.
like I say, its most likly a clogged injector or a clogged VST filter, if it was a valve or a piston issue it would not come and go, if it runs well up to 4400 and then no more I would suspect fuel delivery, none of which will show up on the laptop. you can get the test lamp assy from yamaha for about 70 dollars that will output any codes.<br /> I really did not think the sensor wires would do ya. for one thing the lap top wont give shorts or opens, it will set a code for a malfunctiopn and the ECU mapping will set to default.if the cooling water sensor voltage goes below.1V or above 4.4v the ign control is normal,fuel control is normal and the ISC will be set for a 900 rpm idle, thats alsways a sign a sensor failed.<br /> but a failed coolant sensor has no affect on WOT only increased idle speed.<br />like I said, tie it off, place it in gear, run it up to about 2 k RPM and one at a time remove and reinstall the injector clips, watch the tach closely.<br /> almost any sensor failure on that motor will result in a 900 RPM or more idle speed.<br /> the system does not monitor fuel pressure or flow.<br /> occasionally the ign system will fail but its awful rare. so far I have seen one main relay and one ECU fail on the F115, not bad for a motor thats been out 6 years. both of those failures occued on the same engine 4 days apart.<br /> first symptom was the engine would not shut off, tap the relay with the key off and the engine quit, replaced the relay and it ran fine, 4 days later it was back with an odd power loss. tap on the ecu with my knuckles and it would either run well again or quit. computer said there was nothing wrong.
