2004 F115 Fires but won't Start

[Queequeg2]

check to see what the weather station says the barometric pressure is

I assume I can use YDS to check the running engine to see if they are equivalent?

[99yam40]

I assume I can use YDS to check the running engine to see if they are equivalent?

no, key on but not started.
once the motor is started the manifold vacuum/pressure changes

[Queequeg2]

Pulled the ISC and tested with YDS. It didn't move. I tried it on the port engine and it still didn't move (so it's dead). However, I tested the PORT ISC and it DOES move. I put it on the Starboard engine and tested, doesn't move on that side. I'm assuming something fried the Starboard ISC and whatever it was is still toast. I'll go inspect the wires. If not mistaken, the 2 orange/yellow should be providing 12v. All 4 other wires go back to ECM. Assuming there is power, is there anything else I can look at?

[99yam40]

Pulled the ISC and tested with YDS. It didn't move. I tried it on the port engine and it still didn't move (so it's dead). However, I tested the PORT ISC and it DOES move. I put it on the Starboard engine and tested, doesn't move on that side. I'm assuming something fried the Starboard ISC and whatever it was is still toast. I'll go inspect the wires. If not mistaken, the 2 orange/yellow should be providing 12v. All 4 other wires go back to ECM. Assuming there is power, is there anything else I can look at?

as I wrote before if they stick they can over heat the ECU circuit and burn it out

I have no idea what wires have what voltage.
it is a stepper motor, so it moves in small increments in either direction
what does ISC stand for?

[Queequeg2]

It's the ECM, I retested ISC several times and get sporadic results. Sometimes it moves, sometimes it wiggles a bit, sometimes it doesn't move at all. I can't say if the ISC killed the ECM or the other way. When it happened the engine was idling/running fine. It quit suddenly at idle.

Yamaha manual refers to the ISC as the Idle Speed Con*****er. I think they are also referred to as IAC.

Really appreciate all of your help on this. I was brain locked on the stupid injector and couldn't see past it.

[99yam40]

It's the ECM, I retested ISC several times and get sporadic results. Sometimes it moves, sometimes it wiggles a bit, sometimes it doesn't move at all. I can't say if the ISC killed the ECM or the other way. When it happened the engine was idling/running fine. It quit suddenly at idle.

Yamaha manual refers to the ISC as the Idle Speed Con*****er. I think they are also referred to as IAC.

Really appreciate all of your help on this. I was brain locked on the stupid injector and couldn't see past it.

good luck on the repair.
also check to make sure the manifold pressure matches barometric at key on

I just could not figure out the S part of Idle Speed Con*****er
even tho I had seen it before

[Queequeg2]

The pressure looked ok and I will check again after doing repairs. What does it mean it’s off?

[99yam40]

The pressure looked ok and I will check again after doing repairs. What does it mean it’s off?

as far as I know if it is off then it is bad.
it would lead the ECU to think the motor is at a different elevation, which has different amount of O2 available to burn with fuel it puts into the motor.

I just wanted you to make sure it was not a problem also.
you checked it ,so that is good

[Queequeg2]

as far as I know if it is off then it is bad.
it would lead the ECU to think the motor is at a different elevation, which has different amount of O2 available to burn with fuel it puts into the motor.

Sometimes I really miss the days of simplicity. My old Merc (and even older Evinrude) just ran. If they didn't, trouble shooting was straight forward. My 69 115hp Evinrude once lost a coil and took me back to the ramp on 2 cylinders.

[99yam40]

Sometimes I really miss the days of simplicity. My old Merc (and even older Evinrude) just ran. If they didn't, trouble shooting was straight forward. My 69 115hp Evinrude once lost a coil and took me back to the ramp on 2 cylinders.

But those old carbed motors needed to rejeted if moved to high altitude lakes, these injected 4 strokes should handle it themselves