2003 "Yamaha" 115 EFI

[Junior483]

New reader and member of the forum.

Just bought a new to me 19' bay boat with a 115 4 stroke Mercury (Yamaha from what i understand). If this kind of talk isn't allowed, disregard and let me know.

Engine starts up quickly and idles. Boat gets on plane and gets all of its power. 5400-5500 if I remember correctly.

At idle it will miss and drop a couple hundred RPMs on the tach. Seldom it will stumble until it turns off. Has turned off on me going into gear even if no throttle added. Accelerating will keep it alive.
No detectable unevenness at higher than say 1800ish RPMs.

Idles at around 1000 which is a little high from what i understand.

Spark plugs showing a rich mixture


Fuel injectors cleaned
VST cleaned
Fuel pressure checked and within spec
Intake air temp sensor and engine temp sensor checked for resistance and within spec. Both sensors also have 4.75v reference at the plug
coil resistance checked
new thermostat
IAC rattles after shutdown and hasn't melted. Checked temp with laser and holds just under 100F

Thanks in advance for any help

Will post solution if one comes up. YDS ordered.

[fairdeal]

I don't think its a problem talking Mercaha / Yamamercs here -
our gracious hosts, boats.net also sell Mercury anyway
(never looked to see if they have a Mercury forum, too)

so your problem is a high and unreliable idle.
interesting.

[Junior483]

Im also new at this so don't be scared to sound simple.

will the updated sync/lync procedure allow for more air? could that explain symptoms?

[fairdeal]

I would look to check throttle linkage - the ECM should be con*****ing idle to 750 +/-50 in neutral -
so somethings not right..

the F150 "updated sync/link procedure"?
I don't know if that also applies to the F115

[Junior483]

What should I look for?

I disconnected the throttle link to isolate any tension that may come the cable, no change.

[TownsendsFJR1300]

Post 18 and 21 specifically for the F150, (dunno if this applies to the 115):

http://www.yamahaoutboardparts.com/f...-problem/page2


This, ^^^^, was more related to a low idle, stalling common back then on the F150 (I had the same issue)

[Junior483]

Only getting 4.75 volts at the sensors. Is it suppose to be 5 even? Where does ecm ground?

[Junior483]

Called Merc tech support, they said 4.75v at the temperature sensors should not be an issue. None of the sensors I checked had 5v reference on the nose. Any insight on this?

[Junior483]

Ok seems like at the temp sensors those readings are ok.

TPS and sync next