f115 missfiring

[cyrillefrenchy]

hello , here is my problem today, i just bought a used 2002 f115 100 hours last week, supposed to be in good condition, installed the engine in the boat to replace my old 115 2 stroke, everything went smooth till i took the boat for a ride.
everything was working fine the first 2/ 3 minutes and started to missfiring and banging at the exhaust and i noticed the tach going all the way down to zero for half second an going right back up as soon as the engine worked fine again. the engine is missfiring once in a while, every 10/ 15 ceconds, sometime works fine for 1/2 minutes and missfire again.
the engine bogg down at any rpms, over 2000, no matter if under load or not, i can reproduce the phenomen on neutral at the dock, i just have to give a little throttle over 2000 rpms.
i thought it was the ecm so i replaced it, i have another boat the same engine same year, swapped the 2 ecms, still the same, no difference, still the same engine bogging down.
so i installed a timing light on the spark plugs wires to see if i was loosing spark and yes, i am loosing spark, on all the cylindera at the same time, only for half second and works good again till the next time.
what could cause to loose spark on all the cylinders and make the tach jumping like that?
stator? trigger ?
thank's for any help
frenchy

[99yam40]

bad key switch, bad kill switch, or bad wiring to them are some simple things that come to mind.

Monitoring the input voltages and out puts in the ignition system should tell if the charge or pulsar coils have a problem.

hooking up to a computer would be the best option in my opinion.

Did you see this motor run before you bought it?
if it ran good then maybe you are just looking for a problem in the installation not the motor.

Here is a thread on a F115 that has some interesting info, but I am not sure if any of it would be of any help to you. http://www.yamahaoutboardparts.com/f...e-th15590.html

[cyrillefrenchy]

thank you for the reply, i tried to run the engine with the main harness disconnected after starting , still the same problem so it can't be the harness or switches and also my 115 2 stroke was working fine the day before i installed the 4 stroke.
i agree the best way would be to plug the computer on, but i don't have any so i will try tomorrow to swap stator and pulser coil with another boat that i own and will let you know the result.
and no, i did not see the f115 running before buying but i trust the seller and he says he will take care of me as soon as i find the problem.

[99yam40]

it would be easier to measure voltages than to swap parts out

[cyrillefrenchy]

ok and how do you measure voltage , hom much do i need and on what wire?
do you think i will be able to see the voltage dropping for half second when the engine bogg?sorry i never did that before and i don't know what i should look for.
i will try to take some measurements before taking apart.
thank's again for the help

[99yam40]

I am sure your Yamaha service manual has the testing procedures,specs and the place to measure the pulsar and charge coil voltages at cranking and other RPM. You will also need a DVA adapter for your meter or a meter made to read these peak voltages on these ignition systems.

Does your alarm system function properly?
If something is telling the system to go into safe mode the alarm should go off and it will limit RPMs to 2000. But I do not know if it does that by retarding the timing or killing some cylinders spark
Also some motors use a neutral switch to tell ECU to cut spark on certain cylinders to limit RPM while in neutral.
A Yamaha service manual is a must have

[cyrillefrenchy]

Swapped today the pulsar coil, still the same problem, pulled the flywheel again and swapped the stator, now works perfect. Took the boat for a 10 miles ride at 4500 + rpms, ran like new, problem solved.i looked at my service manual for pulsar and stator voltage, tried to measure before taking apart but did not worked, don't have peak volt meter, easier for me to swap parts. Seller said he will pay for the stator.
Thank 's again for the help
Frenchy

[99yam40]

Glad you got it running correctly.
A DVA adapter is not expensive and it comes in handy from time to time

[cyrillefrenchy]

after a quick search, the dva adapter connected on any multimeter will make a peak volt meter?
this is good then and what kind of measurement do you do with this?
sorry but i am not familiar with that, thank 's again for the help.

[99yam40]

pulsar, charge, and other coil out puts to the CDI, also the out puts of the CDI to the ignition coils.
Also any other voltage readings that the manual states as peak voltage