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2005 F115 TXRD loss of power

T

tomn3

New member
Hi all,
New to this forum and appreciate any help.

I've had a performance issue going on over a month now. Started a while back when I went WOT. Went to 5400 rpm then fell back and stalled. Started right back up and was able to take it slowly up to over 4K. Kept it low until we made it back. Prior to this the motor ran like a champ.(BTW-new to me, very lightly used)
After that took it to the Yamaha tech. Cleaned the VST, compression test(good) and fuel pressure checked out. Was able to get it up to 5K after that. Then it slowly started losing rpm's each trip.

Checked the fuel vent, opened the cap, etc No effect. Had the fuel tank pumped and cleaned.
Went tubing once and had fun but never got over 4k.

Tried tubing again and it died at 3k, had to limp back to the dock.

I was about to buy a test tank and the tech said 90% of the time it's injectors. So I sent them off for cleaning.
Put them in and ran it this evening. Sounded very smooth and quiet. Planed nicely at 3-3500 rpm. But wouldn't go over 4200. Ran a while, backed off to slow speed and tried again. This time it only made 3k and fell back, sputtering worse than ever.

Sorry for the long post.

Any ideas next? Low pressure fuel pump? Get a test tank to isolate the boat?

Thanks for any help.​
 
To determine where your problem is you should put a fuel pressure gauge on the motor (schrader valve on fuel rail - should hold 40 psi) and see if your pressure is dropping off when problems present. With the boat running smooth, I'd guess the problem isn't injectors but a lack of fuel most probably caused by the VST filter. You could try having someone pump the ball up while running to confirm it isn't a fuel supply to VST problem. If the boat was bogging down prior to having the tanks cleaned, your filters could be plugged up again. If you have a separator filter it would be a good idea to pour it into a clear container and make sure you don't still have a contaminated fuel problem. Also have you looked at the fuel in the bowl on the back of the motor?

If you have contaminated fuel, changing out the filters will be a temporary fix until the bad fuel plugs things up again. If the VST filter is plugged, running gas out of a fresh independent tank won't change things as things are already restricted. The VST filter on the f115s is pretty small and can plug up pretty quickly. I went to 2 micron racor filters on my 115s just to make sure I was getting everything out ahead of the motors.

Given the cost of repairs, I think it's money well spent to get the pressure gauge. They don't sell them on this site, and I got mine from Andy at simyamaha.com.
 
Thanks dward,

I had the fuel tank cleaned after the VST unfortuately so you may be correct that I contaminated it after. The fuel and tank did not look too bad according to the guy that did it. I'm wondering if my lines have deteriorated and are breaking down. When the VST was cleaned it had varnish and the mech bead blasted it. Ran ok for some trips but never at full power like before.
I was thinking the test tank just to eliminate the boat side quickly. Then still need to replace lines in my opinion.
I pumped the ball to no avail when the problem was occuring.
I hear the VST is a pain to get to on these. Behind the manifold. I cleaned and swapped mmy injectors by myself with no problem. Think I can tackle the VST?

And you run a 2 micron filter, no performance issues with that? Mine came with a 10.

Thanks again.
 
The boat with the f115s is in Florida and we were having filter plugging problems for a while as the boat wasn't used for a while and the gas got bad. The tanks were also corroding so I replaced the aluminum tanks (100main & 25aux). We initially had one line from the tanks going to the separator and then split to the two f115s. I ran separate lines from the tanks and installed a 2 micron racor filter for each motor. I probably ran 100 miles since the 2 microns were installed and the motors have ran great so far, but with the finer filters I just plan on installing new filters each year. I have a f150 on my pontoon at my home in Minnesota and I run the 10 micron yamaha filter on it. I'm just paranoid about the Florida boat and the ethanol and tank problems I've had down there as a result of sitting idle over the hot humid summers. The racor filters I got spin on to the same head the yamaha fits on.

It looks daunting, but taking the manifold off isn't that big a deal once you get after it. But like I said earlier I really think you should get a fuel pressure gauge as it will tell you a lot about what is wrong. On one of our f115s the fuel pressure regulator was bad, and never would let things get up to 40 psi. If your VST is plugged you'll get 40 psi at idle but when you get to the range where you have performance issues your pressure will begin to drop. If it's just the injectors, you'll have good pressure while motors are bogging down. You can even get the gauges on ebay, but make sure it will fit a Yamaha schrader valve. I got my gauge, along with the filters I installed from simyamaha.com.

If things are falling apart in the lines you should see some debris in the filter bowl on the back of the motor....although changing lines isn't a bad idea.....given what you've described it I'm guessing it isn't the problem. I'd pour the separator into a clear jar and see if you have any gunk in there. I had our tanks cleaned and was still getting gunk. It's also a good idea to get ethanol free gas if you can as the ethanol scours any varnish off of tanks and lines and that can clog things up.
 
I posted this for someone else working on a f115


[h=2]
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Re: 115 Four Stroke Going after the V S T Filter[/h]
Below is my post from your previous thread. There is a link to a couple pictures showing the engine before and after the manifold is removed........you don't need to remove the lower cowling and the intake can be leaned out instead of completely removing it.

You're on the right track. The pump on the back is a diaphram pump that feeds the VST. The bowl and filter on the back has a red disc inside to tell you if there is water in the gas....the red disc will rise up in water and stay at the bottom if no water there. The cartridge filter is to filter between the mechanical pump and VST.

To replace the VST I first removed the plastic air intake from the intake manifold. There are about 2 or 3 bolts that go through the manifold into the block, and about 6 that bolt to the intake itself. You'll need a ujoint and extension to get the bottom bolt. The intake itself has a couple bolts on the intake side and about 5 that bolt it to the block. There are 3 bolts that hold the VST to the intake (mine had yellow paint on them) and I'd wait unitl the intake is loose and leaning out before removing those. There is a metal gasket between the intake and block that you need to remove and keep track of which end is up and down as the bolts don't line up if it's not on correctly.

Once the intake is leaning out, there is a fuel line on the bottom of the VST that is a return from the fuel regulator and the intake fuel line that I removed from the VST. I left the high pressure line to the fuel rail on the VST and removed it from the bottom of the fuel rail. There are also a few vacuum lines that need to be removed from the VST. You'll need a 3/8 drive 10mm, 12mm abd 13mm socket with a 6"extension and a ujoint as the bottom bolt on the plastic intake is down in there. Once the VST is out a phillips screw driver gets the bowl off and then you'll see the VST filter which you replace.

As for the injectors they are a lot easier to get to and may or may not be plugged. It's about $20-$25 each to have them serviced........you decide whether you want to service them now or later. The fuel pressure reading would help you in figuring whether they are plugged up or not. I'd guess that once the VST filter is clean and changed things will run a lot better. I did a lot of research and figured out how to clean my own injectors, but it takes an ultra sonic cleaner and an aparatus to push cleaning fluid through the injectors. I did this because the boat is in Florida and I was on a tight schedule.......if I had the boat around I probably would have had the injectors cleaned by someone like injectorman.com or others I heard about on this site.

Below is a link to a picture of before and after intake is removed. When I changed mine I didn't take the intake completely off, I leaned it out. I also googled "change yamaha f115 vst" and found a bunch of information that helped, and you'll probably find something that I didn't see.

http://www.thehulltruth.com/boating-forum/297623-yamaha-f115-vst-filter-change-w-question.html...-question.html
​
Last edited by dward; 06-27-2011 at 04:29 PM.​
 
Thanks again for all the great info.

Would a pressure regulator be intermittent? The engine was marginal before, cleaned the injectors and I thought I had it licked. Ran quiet and smooth yesterday but topped out at 4200 rpm's, ran that way for 10 minutes. I backed off to near idle and ramped up again. That is where it really dropped off. It ran rough at low rpm's all the way back to the dock. Like it was getting surges of fuel, almost wanting to stall. Even around 1200 -1500. Never did that before.

How about the low pressure fuel pump? I read they're only 30-40 bucks, but it looks like for this F115 it's ~$135.

Tom
 
Mine didn't run rough at low rpms. Get a fuel pressure gauge. If it's the low pressure pump, pumping up the ball will push gas through to the VST
 
Cleaning the injectors without replacing the fuel lines and cleaning the VST is a waste of time and money. You just repaired the result,(Dirty Injectors) not the cause.
 
I think the recommendation to clean the injectors was in response to me telling him I had the tank/fuel cleaned and the VST previously. But it needed to be done anyway.

dward,
I noticed in the manual(Seloc) it gives values for the pressure on the rail with key on/engine off. I've read that it should hold pressure for 5 minutes? I can monitor it underway and I assume it shoud maintain that pressure(close to it) regardless of throttle?

thanks
 
Well, I replaced all the fuel lines I could get to. Replaced the fuel/water separator and the mount. When I looked under it was pitted and corroding. New bulb and I ran new lines from the bulkhead into the motor filter.
Tried to get at the main fuel line under the deck but htat is going to take some planning. The access hole is small and even if I could get the hose off I couldn't get the pick up tube out. So I guess I'll be opening a new hole.
I plan on inspecting the pick up, and remove the filter screen and anti siphon valve if they are there.

II really don't want to go into the VST or injectors again till I have new fuel lines.

Tried taking pressure reading on the rail but I have yet to find a gauge that fits properly. Autozone has one you can borrow, even has a smaller add on fitting. But even then fuel was leaking around the edge and releasing pressure.

Anyone know the size or where one can find an adapter?
 
Ok,
I'm getting nervous reading about removing the fuel pickup. If I screw it up I'm hosed(no pun intended). I'm going to replace the main line and do a fuel vacuum test.
If I read correct that will indicate any restriction in the line. If none found can I assume the pickup is ok? Or I guess an anti siphon valve could be intermittent.
But with all new lines at least I won't have contamination.

Thoughts?
Thanks
 
Was out of internet range over the weekend. The fuel pressure should maintain at about 40 psi when the high pressure pump is running. I believe it's programmed to cycle on for about 3-4 seconds after the ignition is turned on which is why I usually turn the ignition on and wait a few seconds before starting. Once the motor is running I believe it stays on all the time and recylces fuel back to the VST through the fuel pressure regulator. On the f115s the regulator is on the top of the fuel rail. On my f150 it's attached to the VST under the intake manifold. What pressure value did the Seloc manual give?? I have a air regulating valve that I hooked up to my f150 fuel regulator and when I hooked it up and slowly dialed up the air pressure, it started letting air through at 41 psi.

In my opinion if you have enough material coming from the tank or lines that it will plug up the VST or Injectors again, you will see junk in the bottom of your fuel separator filter, and if you do the tank needs more cleaning or replacement. I believe the filters on the VST and injectors are 10 micron. When we first had problems we had a 25 micron Quicksilver separator filter and I thought using a 10 micron Yamaha filter would keep anything from getting into the VST and plug it up. Well I was wrong and that is why I went with the 2 micron racor. If I were you, and thought I might have a contamination problem, I would do what I did and at least temporarily use the 2 micron filter and I would change the VST filter and give things a try. I'm pretty certain that is going to solve the problem. Changing out the VST the first time will take twice as long as the next.
 
tomn3 said:
Ok,
I'm getting nervous reading about removing the fuel pickup. If I screw it up I'm hosed(no pun intended). I'm going to replace the main line and do a fuel vacuum test.
If I read correct that will indicate any restriction in the line. If none found can I assume the pickup is ok? Or I guess an anti siphon valve could be intermittent.
But with all new lines at least I won't have contamination.

Thoughts?
Thanks
Click to expand...

If it's a fuel pick up problem your squeeze ball will flatten out while running due to the suction on the line. If it is a fuel restriction either in the tank or separator filter, pumping up the ball while running will insure fuel is getting to the VST and not starve the motor.
 
Last edited:
Thanks again,
I do have the regualtor on top of the rail. As mentioned I tried taking the pressure reading but it would leak quickly do to the improper fitting. But it did appear to spike around 40psi for the initial key on/motor off. But that's a guess. I agree on the supply side. The bulb has never collapsed as far as I could tell. But I thought I would do the checks while I was in there.

I will replace the main fuel line though. When I was in the motor this weekend I looked in the small filter/seperator on the motor. There was no water but there was some black debris in the bottom(I hadn't checked that in some time). There was none in the external water/seperator, or I guess it could be trapped int he filter elements. I also have the inline filter just after the low pressure pump. The mechanic says that can't be cleaned, just replaced.
The old external lines looked ok. Some white residue but no major flaking as far as I could tell.

Any experience with the low pressure pump? It seems most people inspect and replace the gaskets/diaphrams.

One last thing. When the guy cleaned the tank I was pretty imppressed. He had a good setup. Pumped it out, filtered it, returned it with a spray nozzle to clean the sides and continued to filter. No major debris found at that time.
 
As for checking the low pressure pump, I'd just pump the ball up and disconnect the hose at the cartridge filter between it and the VST and then put the hose in a jar and have someone turn the engine over to make sure it's pumping fuel. I don't have experience with them, but I think I've heard that when they go bad the diaphragm goes and you can get gas going into the engine oil.

As for cleaning the cartridge filter, I just blew air backwards through it, but even when my motors were plugging up it never was restricted. Unfortunately the f115s have a very small VST filter and it will plug up if there is junk in the gas. When I had the 115s plugging up I would pour out the blue Yamaha separator filter into a glass quart jar and there would be about a half inch of brown varnishy looking material that would settle to the bottom. It was junk from the tank that the ethanol was scrubbing off. Hopefully with new tanks, and making sure to run non-ethanol gas, our problems will be gone for a while.

Like I said before.....I think you should change the VST filter and give things a go. If you aren't getting any junk in the big blue Yamaha filter I would think you've taken care of the contamination problem. As for the fitting for the gauge, give Andy a call at simyamaha.com and he should be able to answer what you need.

Good Luck
 
I just purchased a new boat with a new 10/10 F115 TLR but didn't research the F115's before hand. I just went with the overall good reputation of the brand. Was buying one of these engines a seriously big mistake? I could have gone inboard/outboard or chosen between two other manufacturers 2 strokes. Several years of payments ahead of us and I'm worried about my choice of engines. :(
 
It's a great motor and most of the fuel related problems are due to bad gas or ethanol blended gas being used in an older boat/tank. The ethanol scours the varnish out of the lines and tank which can plug up the filters. I'd just make sure to install one of the Yamaha fuel separator filters ahead of the motor, and try to only use non ethanol gas.

As your boat is new you shouldn't have any troubles. I think there are so many f115s out there that you hear about problems when they show up. And I'd bet that on a percentage basis there are very few problems with these motors. If I needed an outboard in this size I'd get another F115........I just wish they had made the VST filter a bit bigger.

Enjoy your boat!
 
I don't have much boat experience but from what I've read I agree with dward. My boat was lightly used for 6 years before I bought it. The motor ran great for 2 months until I think the fuel lines/dirty tank/etc. caught up to me.
The only time it was worked on was to clean the VST. Other than a 6 year old starter rebuild it has all been related to fuel.
And every thread I've been on, regardless of motor, carb or fuel injected, have all shown numerous fuel related issues.
Just keep up with the preventative maintenance and change that water/separator filter.
 
Thanks for the feedback. The boat came with the small Yamaha 10 micron filter installed between the built in tank and the motor. The fuel around here is all E-10 but over the state line within an hours drive of here there is a station that sells good gas. The gas I've used so far, maybe 20 gallons, has been Chevron E-10 and to that I've added Startron and Ring Free. I'm seriously considering switching over to two 6 gallon remote tanks filled with non-ethanol fuel run through a 10 micron water/fuel separator so that I can better keep track of fuel age and condition. If the non-ethanol gas is not available is there any problem in switching back and forth between E-10 and good gas if the remote tanks are run through separate filters?
 
I have two f115s on my fishing boat down in Florida and a f150 on my pontoon at my home on a Minnesota lake. I only use non-ethanol fuel down in Florida, but will use ethanol fuel up in Minnesota on the pontoon for the following reasons:

The Florida boat is an older boat with the newer Yamaha motors, and being an older boat the tanks and lines ended up giving us a ton of trouble after Florida mandated ethanol into their gasoline a few years back. Also the boat in Florida sits idle over the hot humid summer months when there is a much greater potential for condensation in the tanks (moisture and ethanol is a bad combination). The Florida tanks are 100 gallon main and 25 gallon aux in size. My pontoon is newer and the tank is about 25 gallons. So as I believe the risk for contamination and the cost of repair is much greater in Florida, I don't want to risk having problems.

In Minnesota we store the pontoon over the frozen winter months where I don't worry about condensation. And with the smaller tank we are turning it over more often and thus probably keeping the tank clean. Ethanol in our autos keeps the fuel systems very clean as often as we turn them over. So as it's a bit of a pain to insure my kids or wife always get the right fuel I'll accept the ethanol fuel in MN.

So in short I would say it would be better to run non-ethanol fuel through any motor that is stored for periods of time. But as I don't know how long your boat will be stored, and under what conditions, you'll have to decide what you want to use. Frankly if there isn't a station near by that sells non-ethanol fuel, I'd probably use the ethanol blended gas and make sure your fuel separator filter is a good one and in good shape. You mentioned the separator filter you have as being a "small" one. The Yamaha filter I'd recommend is about 3" in diamater and 6" long. I went to two micron Racor filters for the f115s, which is probably over kill, but given what I went through before replacing tanks and lines, I wanted to be sure. I've added a link to where I ordered my filters. Yamaha makes a stainless steel head that comes with a filter for $80.40 (on the link) which is what I installed on all my boats. I added the screw on 2 micron racors (which screw on to the same head) just as a precaution.

As for mxing the non ethanol with ethanol blended gas, I don't see a problem. Just treat it like it's all ethanol when it comes to your stabilizing efforts. And if you have the filter I mentioned I don't see a need to run them through separate filters, just change your filter out once a year and pour it into a glass container to monitor what's in it.

http://www.simyamaha.com/category_s/1734.htm
 
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