Yamaha F115 power loss

[Mazanek]

I have twin F115's. One motor does not come up to full power and drags the other down. Ran well for 3 years then suddenly only will get to 4200 rpm when boat's on plane. Seems to run OK up to about 2500 then seems to run like a 75 hp.<br />Here's what's been done with no effect: Changed plugs, swapped coils and wires from other motor, changed fuel filters (the obvious one and the "hidden" one for the high pressure pump), did compression and leak down tests with good results, checked fuel lines for possibility of sucking air, checked fuel rail pressure, checked to be sure injectors aren't leaky, checked throttle linkage, changed fuel and ran ring free and fuel system cleaner through motor ect.<br />Pumping the throttle temporarily boosts power then it winds down again after a few seconds.<br />Any suggestions would be appreciated.

 

[rodbolt]

Re: Yamaha F115 power loss

do a leak down or at least a compression test. if that passes do a fuel rail pressure test. a quick way to isolate the bad cyl is to bring it up to the problem RPM and one at a time dissconect the injector plug and recconect. do it for each cyl. the one that does not drop is missing fuel, spark, compression or exhaust.check the ign timing. if the TPS is going bad it will be off. when ya "pump" the throttle it moves rapidly and the ECU will widen the injector pulse width to add fuel. the ECU sees it as a rapid acceleration.