2003 F115 Yamaha stalling also would not shut off once

[SparkieBoat]

I have a 2003 F115 Yamaha that cranks and idles perfectly, it also seems to run flawless at WOT and near WOT. But it will shut off or jump and try to cut off when I first accelerate even when not under a load just running in the yard on muffs. When I am running on the river it will also stutter some all through the throttle range until about 7/8 throttle to full throttle it runs perfect. Once it gets warmed up the stutter decreases significantly but will stutter about every minuet or so around 5K RPMs and still stutter some when starting out. I put in new plugs and noticed little improvement. I checked fuel pressure around 46 when motor is off and goes to 38 while running..I did notice that the fuel pressure spikes up about 5-8 psi when it stutters. Today when I was running the motor I turned the key off and it kept running, it normally will take about 2 secs to shut off, but today after about a min I turned the key off and on a couple of times then pulled the kill switch and after about 20 secs it finally sputtered to a stop. I was then able to crank it with kill switch out but it would sputter to a stop after about 8 secs. then it began to work normally again. Any help would be greatly appreciated..I have the factory manual if you need to reference me to a specific page.
Thanks Sparkie

 

[99yam40]

Re: 2003 F115 Yamaha stalling also would not shut off once

Not real sure how the key and kill switch are wired in, but probably they are tied to the same wire. Since they both are not shutting down the motor I would rule them out as it is not common for two switches to fail at the same time.
That would leave the wiring and the connections on both ends and where ever it is tied to, probably ECU.
Since you have the manual then maybe you can find the connection where it lands and then check continuity with a meter between the switches and that connector to rule out the wire, switches, and connections at the switches.
good luck and look through the manual for wiring diagram.

 

[SparkieBoat]

Re: 2003 F115 Yamaha stalling also would not shut off once

thanks 99..I will check that tomorrow..i am suspect of the ecu at this point because of the other problems..a simple bad wire would be nice though. thanks a lot for the reply

 

[SparkieBoat]

Re: 2003 F115 Yamaha stalling also would not shut off once

looking over the manual..it list 4 possible problems for engine not stopping..they are..... ECM, spark plugs, lanyard switch, engine start switch...how in the world could it be spark plugs??? that one has me stumped

 

[99yam40]

Re: 2003 F115 Yamaha stalling also would not shut off once

I think that if the plugs are the wrong heat range and get too hot (glowing)or you have some carbon on them that gets glowing hot, then the motor does not need the spark to keep running.
Just my thoughts

 

[jeffersondodson561]

Re: 2003 F115 Yamaha stalling also would not shut off once

When was the last time you checked/changed spark plugs? If you pull the plugs and look at them they should be a light brown color. Also look at the texture of the plug, if it looks like is has a grit on them that could potentially cause what you are describing.

 

[SparkieBoat]

Re: 2003 F115 Yamaha stalling also would not shut off once

brand new plugs..the old ones were old but looked ok.nothing unusual

 

[jeffersondodson561]

Re: 2003 F115 Yamaha stalling also would not shut off once

You need to verify compression, fuel pressure (pressure regulator too), spark, after that if you still having problems might need to check throttle plate synchronization. This should be done by a reputable shop with a vaccumate.

 

[99yam40]

Re: 2003 F115 Yamaha stalling also would not shut off once

You need to verify compression, fuel pressure (pressure regulator too), spark, after that if you still having problems might need to check throttle plate synchronization. This should be done by a reputable shop with a vaccumate.

What does this have to do with a motor that will not shut off?

 

[SparkieBoat]

Re: 2003 F115 Yamaha stalling also would not shut off once

it may be that I am having 2 issues, 1 causing the will not shut off problem and the 2nd causing the stalling problem. fuel pressure checks out fine, not sure how to test pressure regulator. I will check spark and compression today even though I do not suspect any issues with them, but it is good to make sure. I am also going to check the wiring for the no shut off issue..maybe a loose/bad ground is causing both problems..

 

[99yam40]

Re: 2003 F115 Yamaha stalling also would not shut off once

Sorry, I was focused on the not stopping.
I guess the big question is how does this motor shut down.
Does the ECU just shut down the fuel to make it stop or does it do something to the ignition system to shut down.
Does the manual give you any clues?
Seems like I have read some motors run the pump on full 12 v on key on but then drop back to a resistor to reduce the voltage and pressure while running. If that resistor is failing that could be a problem with the stuttering, but I would not think that would keep the motor from shutting down.
Not sure what would put the full 12 v back on the pump while running to jump the pressure back up, but if it does then it would not shut down if the fuel is the way it is suppose to shut down

 

[SparkieBoat]

Re: 2003 F115 Yamaha stalling also would not shut off once

compression is 160 +- 2 lbs. good spark on all cylinders although the spark did look weak compared to the thick blue streak I get on all my 2 strokes, sometimes could not even see the spark but could hear it popping at 7/16 gap. so maybe it is a weak spark, what other test should I do to check that?? or is that normal?? here are some pics of the new spark plugs after about 2 hours run time, they are in order from left to right 1-4. the number 3 plug was noticeably wet and the other plugs were bone dry..I pulled them from the motor cold.

I included a pic of the old set also.
Ground wire OHMed out fine, key switch and lanyard switch both checked out also.

 

[99yam40]

Re: 2003 F115 Yamaha stalling also would not shut off once

Sparkie you have a PM