Strange performance - or lack thereof.

[snyderpf]

Hello folks....So our 115 4 stroke had been performing not up to snuff for a couple of years. Hesitating significantly until if warmed up after 15 minutes. This year we drained tank, changed filters (Racor water separator and internal low pressure ), removed and cleaned injectors. Boat idled rough, would only run at low rpms, finally lined out on plane, then decreased rpm again. We shut it down, let it cool (5 miles from dock) then restarted and puttered back at rough tolling speed with the throttle at 3/4 to max. After 40 minutes of crossed fingers, suddenly - without doing anything manually to throttle, the boat increased speed, ran up on plane and was going like it was brand new. Felt like injector cleaning made a difference. Ran like a bat outta H... Right to dock. Shutdown and started again - briefly up on plane. Now little confidence and not sure what to do ...........Other than need to get boat insurance paid up.
Any suggestions?? Air in system? O2 sensor? Hi pressure filter? Tank vent line has been checked.

Many thanks,
Paul

[catacom225]

Hi Paul
What kind of fuel are you using, l Hi octains fuels and Bio fuels can cause these engines to run bad .But I'm wondering why it took a couple of years to address the issue, I would look at removing the VST Tank and give it a good clean out to start with

[Moonlighter]

Although it does sound like a fuel related problem, dont completely discount an electrical issue.

I would be checking the white wire connection to the battery positive (or to battery master switch) - any corrosion in that wire or the connections at either end and you get poor or inconsistent power supply to the engine's ecu = poorly running engine. That could easily explain how it suddenly ran well - if a bad connection has moved back to a better connection.