Yamaha F115 model year 2000 won't reach full RPM

Scott_K

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May 24, 2012
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11
I know this is a very discussed topic, but I am unable to find threads where a definitive solution was reached so here goes.

I have a year 2000 Cobia 244 CC with twin F115's and the port engine is not reaching full RPM. Last year the throttle position sensor stuck, and it was surging so I got that replaced, and now it's back to only doing about 4600 RPM max. Starboard engine reached 5800-5900 easily and that puts the boat into a good left turn lol.

I have done the following:
New filters all around.
Cleaned VST filter
Changed VST tank o-ring.
New spark plugs (hotter for F90)
New matched flow injectors.
New thermostat
Replaced low pressure pump diaphragm.
New grommet and spring.
Compression test shows all cylinders within 14% of each other so I think they are OK

The engine does "make oil" I have kept it changed regularly.

All I have read points me next to the high pressure fuel pump and checking the pressure reading under load. I have no clue how to do this and I have seen a Schrader valve on top of the fuel rail, is this the best point to take that reading? What is the name of the part I need to check the fuel pressure?


Thanks in advance!
 
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Scott_K

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Joined
May 24, 2012
Messages
11
I don't know how to perform that, but if you can enlighten me please? I am Googling it now.
 

tommarvin

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Nov 22, 2015
Messages
999
If you have fuel injectors, e-bay has diagnostic software for problems and logging all maintance.
It's about 65 bucks, includes the cable,need tablet or laptop to run it.
 

Scott_K

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Joined
May 24, 2012
Messages
11
Yes I bought that software and cable, it is a bootlegged version of Yamaha YDS and certain key parts of it are not functionally available to use, the menu selections are grayed out so it didn't help me a bit. Seller was apologetic but no refund. I've still got it, it might prove useful for something.
 

tommarvin

Ensign
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Nov 22, 2015
Messages
999
Thanks' for the info, I didn't know it wasn't a fully functioning, and menu selections are grayed out.
E-Bay and Paypal will get all your money back, they protect there buyers completely.
 

Scott_K

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Joined
May 24, 2012
Messages
11
So brought it to a shop, waited three weeks, they tested rail fuel pressure, it was only 20 psi and would fall as soon as engine shut off. The replaced the high pressure fuel pump grommet and the fuel pressure at the rail was a steady 40-45 psi. $452 later I am still only reaching 4200 RPM max on the port engine under normal loaded conditions.

At my wits end, but the mechanic stated he thought the port prop was cupped differently than the starboard. Come to find out, the starboard is a Michigan Wheel SSM-617-II-C 13-1/4 x 17 and the port is a SOLAS T D 13-1/4 x 17 LH

So at this point I am ready to invest in a stainless prop so they both match. They are both in good shape, Any other ideas?
 
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