F115TXRB intermittent issue

[deanpijut1967]

Hello Everyone,

I have posted about this issue in the past. unfortunately i do not have a yamaha dealer in the area. But here is the issue and what i have noticed.

At first start engine idles ok then may die. As i leave harbor the engine will just shut off. no sputter or surging at all. Then restart fine and continue to the open water. After a short period of this then everthing is ok and not one problem the remander of the day.

Today i when i made it to the open water i hit full throttle a hoped it would stay running ok. The rpm will rise and then drop to zero and shut off. On the second attempt I was attempting to put into netural and had hit the trim down button and the rpms came back up. So i experminted. As long as i kept the trim down activated the motor would not shut off. The second i let off the switch it would want to shut off. The as always after a short period 15-20 minutes everything ok for the remander of the day.

The list is long of replacement parts as i mentioned before a brief list that the first mechanic replaced that has since moved away.

ECM
IAC TPS sensor
Fuel pressure regulator
High and low fuel pumps and hoses and primer ball.
VST cleaned and new filter screen. pressure 39 psi
Filter between ball and low pressure pump.
Key switch and kill switch assembly
Therostat and cooling sensor.
sensor on air box.
two harness on engine.
harness to remote box.
main relay.
Also ran on aux fuel tank.

Thanks for any input.
Dean

[Sequoiha]

Have you actually checked your battery cables, sounds like a ground issue to me, do you have a set of automotive jumper cables, hook the jumper cables to the engine and your battery, if this fixes it, disconnect one of the cables ends, if is still fixed then you have identified your issue, easy check anyway.

[99yam40]

I thought the same, but it sounds backwards to me.
Usually a bad connection would cause low voltage when the T&T was energized not when it was released

[deanpijut1967]

installed new battery cables and reload-tested batteries. I know it sounds backwards. But I think when the switch is activated it is providing a path for something that is missing. I wonder if inside the trim tilt relay there are some normally open or closed tips that may be welded that provide power some where else. Or does power thru the harness from engine run thru the gauges and then back or are they for information only. I have a manual and the print is very difficult to read.

Thanks for all of your input,

Dean

[rodbolt17]

what does the lap top indicate for ECU voltage when its trying to stall?
if you have replaced all those parts chasing this issue then I don't blame the last tech for moving.
I would have moved out of embarresment.

[Captain RW]

deanpijut1967 Your parts changer probably moved to Tarpon Springs,Fl. we have more shade tree outboard mechanics than we have **** roaches.

[rodbolt17]

there is another thing to look at, remember the trim,especially when run at a stalled condition is going to lower the batt voltage the ECU "sees".
when this voltage lowers the ECU increases injector ON time,adds a bit of fuel.

[boscoe99]

there is another thing to look at, remember the trim,especially when run at a stalled condition is going to lower the batt voltage the ECU "sees".
when this voltage lowers the ECU increases injector ON time,adds a bit of fuel.

Have you physically seen the injector pulse width increase while also seeing a low voltage condition on YDIS?

[rodbolt17]

yes, its part of the class room training.
its done to insure adequate fuel due to lower injector operating voltage.
what they do about ign voltage loss and pump voltage loss I have no clue.
the fuel pump will run at about 9 volts but pressure may be lowered.
the ecu will work to about 9 V then it will probably go brain dead.
the ign system should work down to about 8 v before all spark is lost.
however if the ecu has gone brain dead there is no telling which systems will remain working.

the 12v for the pump,the injectors and the ign system all come from the same source. the ECU controls the ground path to operate each device.
lose any of them and the system shuts down.

[Nautical]

You never replaced the trim switch??.Looks like the problem occurs when you let off the trim switch. When you engage the switch in down all is good. I would eliminate the trim switch from the equation and just to see what happens.

[rodbolt17]

trim switch works.
leave it be.
has NOTHING to do with the running issue.
the ECU on that motor has nothing to do with trim operation.
it simply does not know.

[deanpijut1967]

I attempted to use the software and when the engine stalled i would loose the communications with the engine.I then monitored with a volt meter and before start 12.6 volts. After start the voltage would start to rise. About 13.8 to 14 volts the engine begin to stall. I repeated few times with same results. Then i would hit the trim down at the moment it began to stall and the voltage dropped to 12.6 and engine smoothed out. Should there be a regulated 12 volts at ecu?

Thanks,

Dean

[rodbolt17]

your describing a voltage loss issue.
even when the engine stalled it should not have affected the ECU, unless the ECU lost voltage then it would think the key got switched off.

even then it should have gone through a shut down sequence.

[deanpijut1967]

The voltage at ecu key on 12.6 volts.after the engine started the voltage would rise to 13.8 to 14 volts then start to stall. After engine stalled voltage remained 12.6 volts at ecu. But the yds would loose communications after the stall. If there is a voltage loss where would it be lost at?

Thanks,
Dean

[rodbolt17]

that I cant answer, have you checked the ISC valve?
have you checked the fuel rail pressure?

12.5-14.8 volts is normal operation.

without looking at the F115 manual I cant remember if the ECU activates the main relay or if the main relay wakes up the ECU.
at shut down,white wire to ground and 12V from the keyswitch removed, the ECU goes into a shut down sequence and cycles the ISC back to 100%.
makes me think the ECU controls the relay.
from what I have seen.
if you ground the white wire and do not remove the 12V it shuts down everything.
if you remove the 12V key on power it may still run but its funny and idles slower.
I had one that the main relay was sticking and the only way to shut it off was turn the key off,which should have killed it but did not, and tap the main relay with a screwdriver handle.

had another that would run until you tapped the ecu with your knuckles.