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Yamaha F115 Recurring Fuel issues

Old 08-07-2020, 11:58 AM
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Default Yamaha F115 Recurring Fuel issues

Recently, I was having issues with my F115 not having power and having trouble planing out. So I replaced the canister filter under the cowling, the filter behind the intake manifold before the VST, and the VST filter. I also replaced the rubber grommet above the VST pump and the VST bowl gasket and intake manifold gasket. Also swapped to a new primer bulb.

I sent the injectors to Brucato FIS and had them cleaned. He informed me that my #3 injector was bad and was not able to be calibrated. So I ordered a brand new one. Got the boat back together and it ran great for 7 hours. Absolutely perfect. Idled better, planned out very easily, very responsive, no stalling when going from reverse to forward, etc. I mean it ran like a brand new one!

So after 7 hours it sputtered once and started running like crap again, hard to plane out, etc.

I did let the fuel get lower than I have ever let it get, then I filled up right before the issue presented itself again.

Also, I realized that I forgot to change my 10 micron filter when doing the VST/injector work.


So now I am back to square one with it. The gas inside of the old 10 micron spin on filter looks fine. I filled up at Holden Beach Marina with non-ethanol.

Think I have a fuel tank issue? It's a poly tank that is very easy to access underneath the console seat.

Or is it likely that one of the other injectors failed? (The previous owner replaced one injector and cleaned the VST right before I bought the boat, and possibly did a DIY clean on the fuel pump and injectors himself). I wonder what would be causing the injector failures?

Also, since the gas tank is so easily accessible by opening the console hatch, is it possible that sunlight has degraded the poly tank and it is dissolving from the inside? How can I rule this out?
Old 08-07-2020, 02:50 PM
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What year F115?
Old 08-07-2020, 03:01 PM
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Originally Posted by B.E. Coyote View Post
What year F115?
Sorry, 2005.
Old 08-07-2020, 03:07 PM
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I have the same engine and year and recently had some fuel issues which were resolved when I replaced the gas tank fuel pickup tube. It looked fine, but on further inspection was brittle and porous which allowed air into the fuel line causing rough operation and stalling. With the replacement pick up tube, the engine runs like it always has - perfect.

One reason why yours may have run well for a while is because your tank was full. A leaking pickup tube would only pick up fuel when the tank is full, then pick up air with the fuel as the tank level lowers.

Last edited by schwammerl; 08-07-2020 at 04:04 PM.
Old 08-07-2020, 03:19 PM
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Run clear plastic section of tygon in between fuel line and see if you have bubbles..
Old 08-07-2020, 04:56 PM
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Originally Posted by schwammerl View Post
I have the same engine and year and recently had some fuel issues which were resolved when I replaced the gas tank fuel pickup tube. It looked fine, but on further inspection was brittle and porous which allowed air into the fuel line causing rough operation and stalling. With the replacement pick up tube, the engine runs like it always has - perfect.

One reason why yours may have run well for a while is because your tank was full. A leaking pickup tube would only pick up fuel when the tank is full, then pick up air with the fuel as the tank level lowers.
I will take a look at the pick up tube.

One clarification, the boat ran great all the way thru the last tank, it was after the fill up that it started running poorly again.
Old 08-10-2020, 12:56 PM
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Bump, ran the boat a little more yesterday. It seemed to be okay at the beginning of the ride, then got worse.

Slow to plane, if I hit the throttle pretty hard it's like it hits a wall and won't accelerate anymore until I back off then proceed to apply throttle more slowly. Just like when I had a bad/lean injector.

Honestly with just my wife and kid on it, it wasn't too noticeable if I went pretty easy on the throttle.

Also, it just doesn't idle as smooth as before and it seems to be idled a bit high, 800-1000 range. Which caused a lot more clunk when shifting.

I want to get this fixed but don't want to keep throwing parts at it.

Old 08-10-2020, 01:10 PM
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Originally Posted by 2Smoker119 View Post
it seems to be idled a bit high, 800-1000 range.
if you confirm that the throttle linkage is not hanging up,
and the throttle plates are closing normally -

then the high idle is the ECM telling us
that something is wrong with one of its inputs
(TPS, CPS, MAP, etc)
You'll need YDS to see which one that is.
Old 08-10-2020, 01:58 PM
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Have you tried clearing the fuel tank vent?
Old 08-10-2020, 02:09 PM
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I had an F115 that did the same thing. It ended up being the pickup tube. Mide would always run great at any speed but full throttle. At full throttle, it would bog and sputter, and then wouldn't get on plane. There was a screen in the pickup tube that was partially obstructed. It would suck the primer bulb flat. Every time the problem occurred, I'd check the bulb and it would be collapsed. I thought it was a clogged vent, but the bulb wouldn't reinflate if I opened the fill cap.

As soon as I replaced the pickup tube, it ran like a raped ape.
Old 08-10-2020, 02:22 PM
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Thanks, I plan to look at the pick up tube and fuel tank vent asap but just haven't had the motivation to mess with it truthfully. and I am leaning towards the VST or injectors being the issue again, since that corrected the issue 100% before. Seems as if something keeps clogging my VST filter or injectors.

I am worried that the VST may be corroding internally but I don't recall seeing any corrosion when I did the VST/Injector work a couple weeks ago.

I guess nothing left to do but dig back into it. Just wanted to get some ideas on where to begin the troubleshooting, as I don't want to just throw more parts at it.
Old 08-10-2020, 02:28 PM
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Also wanted to add, I had my buddy drive the boat yesterday and he was the one who called out the high idle. I hadn't noticed it, but I do remember the engine idling a lot smoother and quieter at a lower RPM after the VST/Injector work a couple weeks ago.

He said he wanted to check the TPS calibration first, haven't had a chance to let him do that yet (he is a Yamaha tech). But like I said, it seems like the VST/Injector work corrected the problem before, so I am leaning towards that, just do not know WHY! lol.
Old 08-10-2020, 02:38 PM
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Mine wouldn't plane at all when I first got it, and my number 4 injector was the culprit. It was washing the cylinder and the compression was low in the number 4. I thought I was screwed and had to rebuild, but 4 new injectors solved it. If it idles rough, pull the injector wires one at a time, and see if it runs the same with one of them pulled. That's your bad injector. Cost $450 installed for a fresh set of four injectors.
Old 08-11-2020, 07:45 AM
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Originally Posted by DavidMeyers View Post
Mine wouldn't plane at all when I first got it, and my number 4 injector was the culprit. It was washing the cylinder and the compression was low in the number 4. I thought I was screwed and had to rebuild, but 4 new injectors solved it. If it idles rough, pull the injector wires one at a time, and see if it runs the same with one of them pulled. That's your bad injector. Cost $450 installed for a fresh set of four injectors.
Yeah I am leaning towards another injector, because 2 others have gone "bad" in the last 40-50 hours of usage. I just want to correct whatever is causing them to go bad.

After I check the fuel tank pick up tube and vent, I will probably order a set of remanufactured injectors from injectorrehab and swap the 2 old ones. I have an e-mail out to BrucatoFIS to see what he thinks on the issue.

Thanks again everyone.

Last edited by 2Smoker119; 08-11-2020 at 09:03 AM.
Old 08-15-2020, 11:34 AM
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Update: I checked the fuel pick up. Looks okay. Not dirty or clogged. Checked the tank vent. Itís clear. I pulled the fuel level sending unit and the tank looks clean. I also pulled my fuel/water separator filter and dumped it. Looks good there. The mount looks clean with no obvious corrosion. fuel line to the engine looks okay, the liner isnít collapsing.

Now back to the engine. The primer bulb pumps up firm and I can hear the needle seat clicking closed inside of the VST.

So I am about to clean the ISC and I realize that it isnít plugged in! Not sure if it popped off or I forgot to plug it back in on reassembly. Although the latter seems unlikely because it ran and idled perfectly for so long.

I have it plugged in and Iím about to retest it. Think having it unplugged would cause any other issues I should look in to?
Old 08-16-2020, 01:31 PM
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Now I am idling at 6 and it sometimes 5 when Iím gear. Seems too low and it did stall once. The engine seems shaky at idle. Not sure i can hear the ISC clicking when I shutdown the engine. I am going to remove the cowling and try again.

the boat runs really good otherwise. No issues planing out today.

Old 08-16-2020, 05:29 PM
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Run it on a 6 gallon tank first. Unless you already did that.
Old 08-17-2020, 06:49 AM
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Small update: I can hear the ISC clicking after shutting down the engine. My tech buddy has been really busy but he says he will get it hooked up to YDS this week. I am going to hold off until he is able to do that. The boat runs well except for at idle now. I can't believe we forgot to plug in the ISC connector. Hope this didn't cause any other damage/issues.
Old 08-17-2020, 11:14 AM
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I am not that patient, so I just ordered a bootleg version of YDS with a cable. Will report back once i get the diagnostic data.

Thanks for the replies everyone.
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Old 08-17-2020, 06:53 PM
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Sounds good. We've also got a low hour 2005 but so far it runs like Walmart - always...With a few threads like yours currently on the board it can only help everybody's knowledge base for this otherwise excellent power plant...

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