F115 Hot Start

[Deltatango]

I have a 2003 Yamaha F115. Over the last couple of years it has been developing a problem with hot starts in the summer time. The motor always starts when cold, however when it has been warmed up and is stopped for more than a 5 minutes or so (but not cooled down) it will crank (at normal cranking speed) but will not start.
The problem appears to be related to fuel supply (or lack of) as if I spray some fuel in the intake it will start.

For the last 5years has always taken 3 sec to start cold (and hot when it does start) It used to start <1sec (would like to know why, but I think unrelated)
Compressions are all even 160-165psi with throttle closed.
Will run up to 5800RPM @ 42 knots
Minimum voltage under cranking is 8v+, quiescent battery 12.4v, charges at 13.6-14v.
Fuel has been run direct with no change in behavior.
I'm running a fuel flow computer, flow drops to zero when I drop down to idle for about 10 seconds then stabilizes at around 2l/h.
New high octane fuel makes no difference
Manual priming prior to cranking makes no difference (manual prime always takes about 3-4pumps to go rock hard)
Advancing the throttle during cranking makes no difference to hot starting
Cooling water is flowing through the fuel cooler
I have not done a code check, but no flashing or warnings shown.
When running fuel rail pressure mid 20's (may be unreliable - didn't have a proper gauge) have not had reliable reading when in no-start condition

When I turn on the ignition for a hot start I usually hear one or two things. A brief hum (which I presume is he HP fuel pump?) and a brief chatter (idle control valve?). I have noticed that when it is not going to start it does both. When it is going to start I only hear the hum...ie no sound from the ICV (or whatever this is called on a Yamaha).

Can reliably be re-started with spraying fuel into intake so some form of fuel starvation suspected (yes I know this is risky).

The boat is 200miles away and I want to make sure I have the right diagnostic tools with me next time I go up there (only had a tyre pressure tool which didn't like petrol, hence not having a reliable fuel pressure reading) have ordered a proper fuel pressure measurement setup.

Any thoughts?

[Deltatango]

http://www.youtube.com/watch?v=2ixjkehOjHw

[Deltatango]

See attached link. Showing failed start condition and stating with fuel spray.

[99yam40]

need to know the rail pressure whenit does and does not start, also if pressure is good then are the injectors firing.

8 volts is real low.
where are you getting that reading from

[fairdeal]

some interesting detail.
a few points:
- the engine runs off its miniature fuel tank - the VST where the electric pump sits - holds about 250 mL. Has a float like a carburetor.
The fact that you can add a few pumps to it before the float shuts tight (and the bulb gets hard) is unremarkable.
Likewise unremarkable that your flowmeter shows no flow for a few seconds at idle, if the VST is full and the float hasn't opened

- yes, the buzz at key on is the electric pump pressurizing the fuel rail. If you put a gauge on then you should see 44 psi.
if so, the engine is ready to start. Once running it should drop to 30-something.

- seems like you are aware of Yamaha hot-restart problems where the engine is flooded (due to excess fuel vapor from the VST vent)
for that opening the throttle wide for more air helps.
Clearly this is not your problem as you find adding fuel helps.

- is the Idle Speed Control valve - ISC Yamaha calls it - a factor? perhaps. I would have a look at it.

I would also want to know what the engine sensors are reporting, particularly for engine and air temperature.

[boscoe99]

8 volts is too low. I don't think some injectors will even work at that low of a voltage. If they do they will open late and close early resulting in insufficient fuel flow to the intake manifold. Might not be the cause of the hot start problem but there is something wrong with the electrics. I would get the low voltage issue fixed first. Then move on from there if necessary.

On a 15 year old motor there are lots of possibilities as to why the voltage is so low.

[fairdeal]

8 volts is too low. I don't think some injectors will even work at that low of a voltage.

I'm sure I've read a Yamaha spec for a significantly higher voltage -

until the OP tells us we don't know exactly where he was measuring.

but FWIW my F225 has always started fine, cold or hot - with this voltage measured at the block / starter lug while cranking:



http://www.yamahaoutboardparts.com/f...nking-f225txrd

[Deltatango]

I'm reading the battery voltage during cranking using the Yamaha gauge which presumably is reading from the distribution lug on the starter solenoid. I.e. the same voltage that the ignition/injection system is seeing. When this problem first surfaced I replaced the battery with a NS70 unit and fitted new terminals, none of this materially changed the cranking speed which to me has always seemed pretty decent. The starter cable is 25mm2 and the runs are short (5.5m centre console).

Probably unrelated, but when I first purchased this outboard it used to run rich and stall when trimmed down. I traced this to flooding of the VST creating a fuel rich mix in the intake runners when the motor was trimmed down and fuel flowed aft down the intake runners. I replaced the float needle and that problem resolved (about 12years ago).

So to summarise what I need to do when I next go to where the boat is:
1. Measure voltage on engine during cranking to verify what gauge is telling me.
2. Try running heavy jumpers to apply a higher starting voltage when engine is cranking without restarting to see if that solves issue.
2. Measure fuel pressure on rail pre-start (cold), during running, pre-start (hot), pre-start (failed start).
3. Use my interface cable (have one somewhere from when I was having problems with some other F115 I owned that had electrical gremlins) to try to read codes. These other engines used to throw codes that came up on the gauge, this one has never thrown any codes on the gauge. Is there a better way these days? Can someone recommend a software/interface cable packages?
4. 'Have a look' at the ICV / ISC - not sure what to look for. I believe that this is the unit that is 'chattering' as part of the shut down and prestart (failed start). The unit idles steadily when it is running, so that seems to be operating normally....

Some more questions:
What role does the ICV/ISC play in starting?
Is there a cold start injection sequence that differs from the hot start - extra injector etc..
What is the correct cranking rpm.
Is there any truth in a comment I read somewhere on one of these threads that a consistent cranking time of 2-3seconds prior to starting is actually a Yamaha error condition warning function?
If my fuel rail pressure (cold) is low does this point toward HP pump failure/pressure regulating valve and if so, how to diagnose which?
If my hot pressure is only low in the crank but no start condition this could indicate low fuel level in VST

[Deltatango]

If my hot no start condition pressure is only low this could indicate low fuel level in VST, perhaps by boiling of fuel/vapour lock? how to investigate that?

[fairdeal]

on a 2003, the voltage you are seeing on the Yamaha gauge is that at the gauge; from the ignition switch. So less the voltage drop coming back from the engine via the 10 pin harness - not sure how revealing that is.

checking the level of fuel in the VST is easy with the primer bulb; you can get an idea of how much its taking by the number of "squeezes" - then you know its full

the Yamaha diagnostic software - available via eBay at a fairly low price - has some utility IMO. You can see "codes" - FWIW -
more valuable the detail of the ECUs sensor inputs - and very easy to test activate fuel pump, injectors, ISC valve

https://www.ebay.com/itm/YAMAHA-Outb...VaIFMa&vxp=mtr

[pstephens46]

Something odd. OP mentions hearing two things when no start hot. HP pump whir and chattering sound of ISC. My motor, F150, pre-sets the ISC when motor is turned off. To 100% as Rod has told us in the past. Why would it change at key on ? Rod has explained the ECU does not "know" position of ISC. It only requests it to set. At key "off" in the case of resetting for the next start sequence. Would be interesting to see/hear this in person.

Is the damn thing closing when he is having the issue?

[rodbolt17]

that chatter at key on is not normal.
the ISC should only chatter at key off.
if you have an electrical connection issue the ECU may have seen a key off .
at 8v at the starter think of what the ECU is seeing.

[Deltatango]

If you listen to the video - posted above, with the volume up, you can hear the ISC chatter on key on.

[pstephens46]

That's bizarre.


Do you hear it chatter at key off when you shut down?

starter turns the motor pretty quick to only have 8 volts at lug.

[99yam40]

If you listen to the video - posted above, with the volume up, you can hear the ISC chatter on key on.

You have been told this is a problem, start looking for where the electrical is being dropped