F115 Hot Start

[Deltatango]

Thanks for all the valuable comments. I was briefly able to run some pressure tests on the motor this afternoon before having to leave the water.
It seems however that fuel rail pressure is not the culpeit. I have posted three videos.
1. Cold start (successful)
2. Hot start (successful) within about 10min of waeming up engine thoroughly at a range of throttle settings including some runs at WOT.
3. Hot start (unsuccessful) after sitting with motor stopped for 15min watching the rail pressure gradually bleed down to 20psi.

[Deltatango]

Here’s the link of the motor successfully starting about 5 minafter warming up

[Deltatango]

And here it is on a cold start

[Deltatango]

I’ll take some heavy jumpers up next weekend and see if I can replicate the problem with higher voltage at the starter. See if the isc chatter goes away then.

[Deltatango]

Still struggling with the diagnosis of this. Could someone confirm what type of pump the high pressure pump is on this engine. Displacement or centrifugal. Want to know if it I possible for the pressure I'm reading on the rail is vapour.

[rodbolt17]

it is a positive displacement blow through pump.
however it is not your issue.
myself I would figure out what part of the electrical system has failed.
a spark test on the hot restart would be good.
but your basic battery voltage drop is way to much.
however it is easter.

[TownsendsFJR1300]

I don't hear the ISC chatter at start up NOW, just shutting down(normal)..

I'd think, with the spritz of fuel NEEDED for hot re-start (going thru the TB's it starts), the injectors aren't "firing off".

As noted, low voltage for the injectors/ECU to fire off (and provide fuel)?

[Deltatango]

Voltage at the starter is 8.5 on cranking whether cold, hot or 15min after a hot shut down. Only the latter causes a no start.ie The problem occurs in an envelope of about 30min after a hard run. from 15min after shut down to 45-60min after shutdown. Outside this envelope it will start and the ISC will not chatter on start-up.

The ISC chatter on key on is a consistent occurrence for the hot no start condition, maybe hard to hear on the latest video. I suppose that even if the ISC is closing down for some reason (low voltage/fault in ECU or other) presumably that would be overcome by simply tying to start the engine with the throttle open. Is this a valid assumption?

Is there any failsafe condition that might be related to engine temperature if the block heat soaks and temp rises during this time window. Any test I can do to see if my ECU is developing a heat related fault

Spark does appear to be there during fail but it does look kind of weak compared to what I am used to seeing on a 2stroke.

[rodbolt17]

guess what
a hot engine is typically harder to turn than a cold one at temps above about 50*F.
means the starter is a dead short and most the available current is being used by the starter not the ECU,IGN system or the injectors.
you have a limited amount of current that must be shared. the starter looks like a huge short circuit electrically.
at 8.5V at the starter lug the current still has to make the path back to the keyswitch,acrossed the keyswitch and back to the motor.
by the time that 8.5V hits the ECU it may be as low as 7V.
ign takes 12V,pump takes 12V sensors need 5V, ECU needs 12V.

[Deltatango]

Managed to increase the voltage at the starter lugs from 9.1v to 10.7v by running a very heavy pair of jumpers (50mm2). So going to manufacture a heavier set of start leads and ditch the crappy BEP isolation switch (0.1-0.2v drop across switch). Confident that these are not the issue but acknowledge that these things are not helpful in the efficient operation on the engine. Why am I confident these are not related to the problem? Because something (presumably the ECU) is incorrectly racking the IAC every time we have a fail to start at key on, and this happens before cranking occurs when voltage is not depressed by the starter.

Also making up a new tank pickup to eliminate a suspected air leak on the fuel tank pickup that uses an OMC plug fitting. Not sure how this could be related to the issue, but don't like the idea of using the VST to separate out air from fuel unnecessarily.

Still haven't got the Yamaha software package to load on my computer, but that's another story.....will be interesting to see what error codes might be sitting in there...

Phil

[Deltatango]

Water temperature has come up (midsummer here) and the hot starting problem has returned. Since I last posted I have replaced all the starter leads and reliably getting 10.5v plus at the starter. Coincidentally the starter failed a few months ago (commutator damage) and the new starter motor is cranking much faster than in the video's I loaded, I thought that might have fixed the problem somehow but no. I'm thinking about spraying some freezing spray (for testing electrical components) onto the CPU to see if I can get a more rapid return to normal operation.

[Rbnorris1]

Had this same problem, 2004 F115 I bought two years ago. After researching and reading several posts on several fora, I decided to approach it as a overheating problem. I installed a double-valved "Y" connector to the livewell pump and ran a piece of 5/8" hose with a check valve and garden hose connectors on both ends. Attached the female end at the "Y" (turned "Y" valve off to live well), and attached the male end to the block flush connector hose. When I stop from making a good run, I turn on the livewell pump which runs water continuously through the block AND the fuel cooler (which flows to the pee hole discharge). Since installing and using this setup, I have NEVER had a recurrence. I'm thinking its a fuel temperature problem at hot shut down. I've read that this has been an issue in the 2002-2005 F115's (I owned a 2001 F115 prior to this one and never had the problem). I've also read that Yamaha would not admit the problem but did have some expensive fix they would sell you. My simple but maybe a little awkward fix cost me less than $40 for parts. The check valve prevents water from backflowing from the engine to the livewell pump while the engine is running. All I have to do is to remember to switch off the livewell pump when I restart the engine.

Other than this, I have never had an issue with the F115. It performs like a champ!