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OUTBOARD SURGING AND CUTTING OUT AT HIGH RPMS

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Bigdog2u

New member
Hello. I have a 2003 Mercury 225 4-stroke EFI that has less than 200 hours on it. It quit running so a local mechanic replaced both the high and low pressure fuel pumps. It runs fine now except when I throttle up under load until I hit about 4500 rpms. Then the motor starts surging and idling down to idle. Motor doesn't sputter or quit just surges and idles down at high rpms under load. I replaced the fuel/air mixture sensor and that didn't fix the problem. Both local mechanics are kind of stumped. I'm getting really frustrated. Anybody have any suggestions for a fix??? Thanks.
 
That is the issue with high tech 4 strokes.-----Very hard to find a local shop with the expertise to fix them.-----A big problem where there is a short season and marina staff is out of work in winter time.
 
That is the equivalent of a Yamaha F225TXRB model.

Has a pressure gauge been installed on the motor so as to see what the fuel pressure is doing when it starts to surge and the RPM decrease?

What is the fuel/air mixture sensor of which you speak?

There are at least three fuel filters. Primary filter at the front of the motor. F shaped filter outside of the vapor separator tank and the high pressure fuel pump filter within the VST. Which of these two were replaced.
 
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