F115 4-Stoke 2003 on Pontoon boggs down at WOT

[DTOWNS]

Desperately need help. Our 2003 Yamaha F115 4-stoke engine (has about 175 hrs on the motor) is only putting out about 2500 RPM at WOT. We have already, tried an external fuel tank (no issues with fuel line or filters), changed spark plugs, changed one coil, ran a diagnostic system (while running in the lake) that showed all sensors are good. Tested the TPS with Meter, had the prop/hub looked at by a local shop (no recommendation to repair/replace 13.5 diam./17 pitch) also check the pontoons no water inside that would cause drag. When in the water it idols fine and goes about 3/4 of throttle fine...then no advance (and reverse is fine). Sometimes (not always) it has a consistent beep after running a few minutes but when we turn it off and restart it the beep goes away and doesn't return while running the boat. Can anyone give me some advise what to look at next...compression? This is a Landau, Quest 22' fish pontoon boat with 3 toons weighing in at 1640 per specs. Thanks for any and all thoughts. About ready to take it to the shop but don't have a trailer and not sure based on the reviews that it is the best option (especially without trying once more to find the issue...with your help).

 

[rejesterd]

That constant beep is the thing to focus on. That typically means your engine has gone into a low-rpm control mode, because the computer sensed either overheating or low oil pressure. The diagnostic system should tell you if the oil pressure switch or the thermoswitch have activated. If it's an overheat warning, replace the thermostat and the impeller. If it's a low oil pressure warning, then you can try measuring the oil pressure to see if it's within spec (as it might just be a faulty switch activating when it's not supposed to). Otherwise, just take it in to get looked at by a pro.

At only 175 hours, I wouldn't suspect low compression.

 

[DTOWNS]

Thanks!...will work on that and get back with you.

 

[DTOWNS]

Since we ran the diagnostic already and it didn't show any switch issues...would there be a reason it wouldn't show up on the diagnostic? Also, when the beeping happened it was in idle mode once we gave it some gas, it stopped.

 

[rejesterd]

I would think Yamaha diagnostics (YDIS) would show those, but if not, then the best way to proceed is to get the service manual. It will tell you how to test the switches when they're removed from the engine. Then you'll know for sure if one of them is bad.

But more importantly, it's best not to run the engine while it's in a control mode if you can help it. So maybe test the switches first. If they check out ok, just blindly replace the thermostat and the impeller. Then at least you can be pretty sure the cooling system is working. If you still get the beep and can't get past 2500 rpm, assume there's a problem with the oil pump (in which case, you'd need to take it to a pro to get it fixed).

 

[DTOWNS]

Another resource seem to think if the YDIS doesn't show it in RPM reduction mode it could be the computer is bad. If the switches are good would you assume the same. Is there a way to check the computer (and is the CDI what is being referred to as computer)? Is there a way to reset it once it is in this mode?

 

[rejesterd]

I've never had YDIS connected to my engine while it was in a control mode, so I can't say if that's right or wrong. But your engine's computer is called the "ECU". Your ignition system is either TCI or CDI.. but the test for it would be the same regardless: measuring the output peak voltage from the ignition coil. The service manual will have specs for what the peak voltage should be at cranking and certain engine speeds. You'll need a peak voltage meter/adapter as well.

But the computer can fail in weird ways, so the peak voltage test isn't always conclusive. So better to make sure the thermoswitch and oil pressure switch test out ok, make sure the impeller and thermostat are good, and measure the oil pressure to make sure it's good. If you still get the beep after that, then yes, it certainly could be the ECU.

 

[99yam40]

has this boat and motor ever ran higher RPMs for you?
or is this rig new to you and never run as it should?

have you read any Yamaha performance bulletins on a rig like your to see what props they used and what RPM/speed they got?

monitor fuel pressures while the problem shows up.
that should at least tell you there is or is not a fuel delivery problems