F115 idle trouble shooting again

Hi,
I have a "funny" iddle problem on my F115 (2003), I am trying to explain and find some help.
When I start engine, it starts immediatly and after a few seconds it idlles at 700 rpm, OK very good, like new. After a few minutes, engine begins to cough and stops.
When I start it again, it does not start immediatly but only after 2s ou 3s and a lot of motor rounds and then it iddles at 900-1000 rpm even with gear engaged which is to high for me. (at 900rpm boat speed is 3.2 knt)
This problem remains independant if motor is cold or warm.
So, randomly, if engine starts immediatly and I run at 700rpm, it stops after a few minutes and if it starts after a lot of rounds, it runs at 900 rpm and does not stops, I don't know if I am clear ?
I cleaned VST an ISC, I adjust TPS and fuel admission is perfect, change fuel filters, thermostat is new.
F115 runs perfect at higher speeds and WOT (5600rpm)

If someone has got an idea about this problem, I would be very pleased.

Many thanks
Lo?c
France

Re: F115 idle trouble shooting again

either the ISC is sticking,the ECU is failing or a code is set causing the engine to default to 10*BTDC and causing the high idle.
check for codes,while its acting up, or use the diagnostic test lamp.
no codes are stored but if active either the laptop or diagnostic lamp will display codes.

Re: F115 idle trouble shooting again

rodbolt said:

either the ISC is sticking,the ECU is failing or a code is set causing the engine to default to 10*BTDC and causing the high idle.
check for codes,while its acting up, or use the diagnostic test lamp.
no codes are stored but if active either the laptop or diagnostic lamp will display codes.

Click to expand...

Thanks Robolt, but what means BTDC ?
Yamaha retailer do not want to come with laptop at the boat in my country and what is a diagnostic lamp ? How does it work ?
So, this is to make a diagnostic and then, if a code is set, what must I do ?
Many thanks,
Lo?c
France

Re: F115 idle trouble shooting again

the F115 uses a relativly low power ECU, its kinda stupid.
it does monitor most sensors for failures. the ISC is NOT monitored for mechanical failures.
map,IAT,ECT and pulser coils ARE monitored.
if one fails or is out of range the ECU defaults the ign timing to 10degrees Before Top Dead Center instead of the normal idle timing of about 2 degrees after top dead center.
this causes an idle speed of about 900 RPM.
depending on the sensor failed top speed may or may not be reached.
the diagnostic test lamp plugs into the gray connector the laptop uses and the capped blue wire beside it.
it can flash active codes but cannot store them.
the laptop can record about the last 13 minutes of engine operation and graph most functions for later diagnosis.
once a code is discovered as set the next step is to physically check the suspected sensor and circuits.

Re: F115 idle trouble shooting again

rodbolt said:

the F115 uses a relativly low power ECU, its kinda stupid.
it does monitor most sensors for failures. the ISC is NOT monitored for mechanical failures.
map,IAT,ECT and pulser coils ARE monitored.
if one fails or is out of range the ECU defaults the ign timing to 10degrees Before Top Dead Center instead of the normal idle timing of about 2 degrees after top dead center.
this causes an idle speed of about 900 RPM.
depending on the sensor failed top speed may or may not be reached.
the diagnostic test lamp plugs into the gray connector the laptop uses and the capped blue wire beside it.
it can flash active codes but cannot store them.
the laptop can record about the last 13 minutes of engine operation and graph most functions for later diagnosis.
once a code is discovered as set the next step is to physically check the suspected sensor and circuits.

Click to expand...

Ok thanks Robolt, I do not understand your English abreviations (map, IAT, ECT...) because they are not the same in french.
However, if I connect a 12v lamp into the laptop connector, could I read the code error ?
I think it is like ON,OFF,ON,OFF .... and it means 1010... ?
Thanks again
Lo?c

Re: F115 idle trouble shooting again

ok
you cannot randomly stick stuff into the ECM diagnostic connector.
however in the F115 mercury manual from about 2001 to 2005 they give a diagram on a homemade test lamp or you can order the one from yamaha for about 79 dollars.
IAT,intake air temp,ECT engine coolent temp sensor,MAP manifold air pressure sensor.
this is a simple speed density EFI system.
google speed density EFI and there is a lot of info on how a speed density system works and there isnt but so many ways to make one.
ISC is idle stabilizer valve,the rest of the world calls it an IAC,Idle air control valve.

Re: F115 idle trouble shooting again

rodbolt said:

ok
you cannot randomly stick stuff into the ECM diagnostic connector.
however in the F115 mercury manual from about 2001 to 2005 they give a diagram on a homemade test lamp or you can order the one from yamaha for about 79 dollars.
IAT,intake air temp,ECT engine coolent temp sensor,MAP manifold air pressure sensor.
this is a simple speed density EFI system.
google speed density EFI and there is a lot of info on how a speed density system works and there isnt but so many ways to make one.
ISC is idle stabilizer valve,the rest of the world calls it an IAC,Idle air control valve.

Click to expand...

Thanks Rodbolt, very clear now.
I remove all this components and they seems to be in very good conditons, like new, no dust, no grease, no smoke..
I started engine without ISC connected and yes it runs immediatly at 1000rpm, so faulty.
I check ISC but it is impossible to unmounted it, is it recommended or not to lubrify it with WD40 ?
Another way, do you think ECT could cause this randomizing iddle failure ?
Thanks again
Lo?c