Power issue 2520 with 2008 Yamaha 250

[Daddy Mackarel]

I have had a rough year and wasn't able to get out much and now my Parker is jacked up. I think my fuel went bad and that started a cascade of issues. It is powered by a 2008 Parker 250 with around 1200 hours on it. Always took care of it and usually have used Ringfree. Ran great until the last 6 months or so. I was quite convinced it was caused by old ethanol-laden fuel that we dealing with here in California. I had a fuel service with new plugs, etc, had my fuel system cleaned, tank polished, dumped most the fuel (now I wish all!) but had the rest professionally run through filters, replaced my Racor fuel filter and water separator twice and even replaced the fuel filter on the motor and the associated water sensor. Fuel is mostly new and now looks good. It runs great at low speeds and then, if I run fast for a while, it gets throaty and the check engine light comes on. After this happens, it loses a lot of power but can still keep RPMs on the upper ranges. I then have to turn it off but can immediately restart it and it runs OK. Once this happens, I can only go one to maybe five minutes of running fast before it happens again. However, I can troll all day with no problem including after this happens. The weird thing is that it initially runs great for about 45 minutes even at high speeds. I don’t know if it is a heat related issue or what but certainly seems to be a lack of fuel, air or vapor lock. Before I throw more money at this, I am going to try a T valve to switch over to a separate fuel tank after it happens once. This will confirm it an engine issue vs something up stream. Not sure how else to figure this out. I am working with a mechanic but he now isn't sure why this is happening.

some ideas that I've come up with: fuel pump, air leak at the Racor, bad fuel, bad anti-siphon check valve, fuel injectors.

Any input would be appreciated! The tuna are far right now and I can't do the run until this is sorted out!

 

[got_em_on]

I would run off the temporary tank first-not after it happens. This will get you pointed in the right direction quicker.

2 things are going to happen-1. It will run great and problem wont occur. You just eliminated engine issues and know to start trouble shooting fuel supply. Or 2-it will occur again and you just eliminated fuel supply to engine and know to start trouble shooting motor.

Some basics you probably checked but asking anyway-If engine light is coming on is there a code mechanic can check on? Feel the water out coming out of engine before and after it happens. Does temp change and get really hot?
Is primer bulb soft after it happens and is it pointed in the correct direction upwards.
Fuel vent clogged?

Good Luck

 

[Brent]

I agree with the person above.

Has VST been cleaned and filter replaced?

What is the fuel pressure on the rail?

Do you have a factory shop manual?

 

[Brent]

I agree with the person above.

Has VST been cleaned and filter replaced?

What is the fuel pressure on the rail?

Do you have a factory shop manual?

 

[Brent]

On a related note, when were the thermostats and water pump replaced?

Anodes ok?

 

[shawnee83]

I was going to mention the Thermostats and the water pump. Especially the Thermostats as they need to be changed every other year or so (200 hrs). If they fail stuck open or partially open, they can cause issues.

 

[Daddy Mackarel]

Just realized I never replied with the cause. It was the starboard cam shaft position sensor. The key is NOT shutting down before checking for codes - some codes disappear when you turn off the motor. Two long time Yamaha mechanics didn’t know or mention this after hours of trouble shooting.

 

[Efx]

This cam sensor sure creates a lot of difficult intermittent problems. Not only in boats but in cars. It’s my first look from now on.

 

[Brent]

Just realized I never replied with the cause. It was the starboard cam shaft position sensor. The key is NOT shutting down before checking for codes - some codes disappear when you turn off the motor. Two long time Yamaha mechanics didn’t know or mention this after hours of trouble shooting.

YDS does key on testing with motor off and motor running tests

is this what you meant? and mechanics just did key on and motor off testing?

 

[Daddy Mackarel]

No. The code actually clears when you shut the motor off. I didn’t realize this was possible but apparently some codes don’t stick around while others do. It started running bad and so I shut it off and turn it back on and then there was no code. I was able to retrieve the code when I left it on and checked. Sort of a “duh” moment but no one had ever mentioned codes disappearing was possible

 

[Brent]

Thanks