Help!! Problem with new 2016 Mercury 75 outboard-gctid805091

[jeffspalmcoast]

Help!! Motor runs smooth till it hits about 2500 rpm then it sputters and shakes. Happened suddenly when i was cruising on the lake at about 28 mph the engine just started to slow down and running rough. I was able to limp back to the boat ramp at just above idle speed. I replaced all the gas (portable tank) this weekend after the problem and the low pressure fuel filter but still runs rough and shakes at anything over 2500 rpm. Only 60 hrs on the motor. Any suggestions on what to check?? I dont want to trek to my dealer if i can avoid it.... Thanks Jeff

[Norton_Rider]

One of two things may be going on:

[ol]

[li]The engine has a sensor that prevents the engine from over-reving in neutral. The ECU is set to rev no higher than 2300-2500 RPM when it senses it is in neutral. This sensor may be bad.[/li]

[li]The ECU puts the engine goes into a "limp-home" mode if there are major issues. The issue could be real or it could be a bad sensor.[/li]

[/ol]

In either case, I think you should have a dealer look at it.

[Chief_Alen]

Could the engine be overheating for some reason and going into limp mode ?

[FISHIN00]

I would take it to the dealer and have him plug into the ECU and trouble shoot....could be a minor issue. If you are the original owner the motor is under warranty.

[jeffspalmcoast]

Thank you guys for the help!! Off it goes to the dealer. If its a bad sensor and goes into limp mode, would the engine still run rough at slower speed (1200 rpm)? I would think it would run ok till you tried to get up past 2500 rpm.

[jeffspalmcoast]

Not overheating. Was at about 160deg when it shut down to limp mode. Thanks Jeff

[Norton_Rider]

It depends on how Mercury implements their limp mode.

I had a similar issue with my Suzuki 20 EFI outboard. It had a bad sensor that was activating the rev limiter. From the feel of it, Suzuki's rev limiter works by cutting ignition and/or fuel to one cylinder; so it runs very rough in this mode. In my case the engine would idle fine but the roughness would kick in right above idle. The sensor was replaced under warranty.

[jeffspalmcoast]

Would you believe it was a bad gas cap?? Cap wasnt letting the tank vent as gas was being used and caused a vacuum. Computer went into limp back mode as it was starved for fuel. Even after I opened the cap the engine still ran in mode. Tech said its a common problem. I needed to shut it down and computer would then reset after a few min. He said " You must close the cap then back it off a 1/4 turn after filling up". Why wont it run past 2500 rpm in my driveway on muffs?? Computer has a built in rev limiter at 2500 in idle. Ran the boat all day yesterday and all was good!! Live and learn!!