Yamaha 250 throttles down at high RPM

[bigdogg1]

Is this a thermostat issue? My Yamaha 250 w/ ~ 250 hrs starts fine, idles fine, accelerates fine and travel very well at RPM up to 4500RPM. However, when I open it up to 5500+, it decelerates right down to a troll within 10 seconds. After turning the engine off and on again, we can get back underway and hit up to 4500 RPM again without issue.

I am wondering if the Tstat needs replacing or are there other issues that others have encountered with similar symptoms?

 

[silversands]

My neighbour had and engine that would die right off and only idle and it was a faulty temperature sensor. Engine was shutting down to protect itself..but engine was fine..just the sensor. So could be oil pressure or temp. sensor gone bad..just some ideas...

 

[ryanb]

Sounds like a fuel issue perhaps. Check your filters and pumps.

You should be getting alarms if it's entering safe mode to protect itself with a faulty thermostat.

 

[bigdogg1]

Thanks for the ideas - long weekend coming up, hopefully source out the culprit whether it be a sensor or a filter.

 

[noluck]

is your alarm working? does it come on when you turn the ignition on

 

[bigdogg1]

Great question noluck. This is a new-to-me boat and the alarm does not come on when the ignition turns on. I have been looking into whether alarms are on every ignition set up and even a Yamaha dealer gave me opposing information on this. Does every setup have an alarm that chimes prior to ignition?

 

[CIVANO]

My 2004 250 yamaha does not have alarm come on prior to ignition

 

[Pineapple Express]

I've got a 2007 Yamaha F250 3.3L V6. No alarm on startup.

 

[pescador]

My 2003 F225 nor my 2019 F250 have/had an alarm come on at start up.

 

[Klob]

Get it hooked up to a computer at a shop. Hopefully faulty sensor.

 

[uclueletcharters]

check your high pressure fuel pump and screen on pick up it's located in a small tank located on the side of your powerhead.

 

[bigdogg1]

check your high pressure fuel pump and screen on pick up it's located in a small tank located on the side of your powerhead.

Thanks - will head out tonight to see if the new separator and thermostats made a difference. All 3 were in need of replaced (even changed out the holder for the separator). Saw another post elsewhere about the High Pressure pump-now just need to find it ).

 

[BigReel]

I went through this exact issue with my F250 motor last year. Would run fine then power down to limp mode. Only solution was key off then back on and full power was restored for a short period of time. Took it to the dealer and after expensive testing and diagnosis it was determined to be a Sensor. The motor has variable valve time and 3 sensors along with it.

Things that were tested until problem was solved. It eventually went to the Yamaha Rep/specialist for the island.
High Pressure fuel pump and filter (forget what it's called but common problem and they cleaned it out).
Swapped ECM and had the same issue
Had laptop hooked up while running and logged pressures and timing.
Had plugs and oil and compression while in there.
Read codes. Cleared and reset.
Sea trials
Etc etc.

$300 sensor fixed it. Ran like new.

 

[pescador]

I went through this exact issue with my F250 motor last year. Would run fine then power down to limp mode. Only solution was key off then back on and full power was restored for a short period of time. Took it to the dealer and after expensive testing and diagnosis it was determined to be a Sensor. The motor has variable valve time and 3 sensors along with it.

Things that were tested until problem was solved. It eventually went to the Yamaha Rep/specialist for the island.
High Pressure fuel pump and filter (forget what it's called but common problem and they cleaned it out).
Swapped ECM and had the same issue
Had laptop hooked up while running and logged pressures and timing.
Had plugs and oil and compression while in there.
Read codes. Cleared and reset.
Sea trials
Etc etc.

$300 sensor fixed it. Ran like new.

what year is your motor?

 

[BigReel]

what year is your motor?

2008 800hrs

 

[bigdogg1]

Mine is a Sept 2011 F250 TXR ~ 300 hrs

 

[bigdogg1]

I went through this exact issue with my F250 motor last year. Would run fine then power down to limp mode. Only solution was key off then back on and full power was restored for a short period of time. Took it to the dealer and after expensive testing and diagnosis it was determined to be a Sensor. The motor has variable valve time and 3 sensors along with it.

Things that were tested until problem was solved. It eventually went to the Yamaha Rep/specialist for the island.
High Pressure fuel pump and filter (forget what it's called but common problem and they cleaned it out).
Swapped ECM and had the same issue
Had laptop hooked up while running and logged pressures and timing.
Had plugs and oil and compression while in there.
Read codes. Cleared and reset.
Sea trials
Etc etc.

$300 sensor fixed it. Ran like new.

What sensor was it btw? Do you recall?