No power under load? Anyone?

[flatsprowler]

I have a 2003 F115, its been running horrible under a load. When I have it in nuetral or idle it runs fine and will even rev up to the 45-5000 rpms in nuetral.
If I try to get on plane it just won't run under a load. I have tried running it off an external gas tank, still the same problem. The engine was recently serviced, new plugs, oil change, new impeller, gear oil, injectors cleaned, etc. It ran for about an hour fine when I got it out of the shop but went right back to the same- won't run under a load. I checked to make sure all the plugs were firing and they are. gas is from an external tank. I'm at a loss.
Any suggestions? I have heard that these are symptoms displayed when a power pack goes bad. I don't guess its the fuel pump or injectors if it will rev up in nuetral. I'm scratching my head here.

 

[reeldutch]

Re: No power under load? Anyone?

after the tune up it run fine for 1 hour?
was the engine connected to the main tank or remote tank during that hour?

also i would check battery voltage, fuel pressure, and spark running it under load and that will tell you whats going on.

how is the compresion on the motor.

i know on 4 strokes you should perform a leak down test to find out whats going on.
but a quick compression test gives you a desent indication.

say you have 3 cylinders of 190 psi and one of
140. than i would suggest to bring it to a dealer to get it checked out.
loosing compression is loosing power under load.
in nutral on mufs you could rev up only 2 contributing cylinders up to 5500.
bud not under load.

could be leaking valves bad rings , blown gasket.
let the dealer do a leak down test if you have a low compresion situation


i would take a fuel sample.
compresion test it.

if everything is normal i would do some trouble shooting.

like i suggested.

 

[rodbolt]

Re: No power under load? Anyone?

I agree with reeldutch.
your implication is this was the reason for the first tuneup/injector service.
if the cause of the first issue was not corrected the issue will return. its a simple fact of life.
two things,minimum, you want to see at your dealership. 1 is at least the certificate of completion of 4 stroke systems,advanced 4 stroke would be even better. 2 is the correct test wheel for properly loading the engine for testing and verification of the repairs.
ECU failures and not real comon but I have seen more with the F115 than any other yamaha.
but before condeming the ECU its imperative to test all other subsystems as well.

 

[flatsprowler]

Re: No power under load? Anyone?

Ok thanks a bunch I will give these a shot and let you know the results.
To answer your question about the fuel, we thought it might be fuel due to some water getting in the tank, the shop drained about twenty gallons until the fuel started to look clean again and took it out for a test run, said it ran to 4000 rpms and they thought it was fine. (The manual says if it is running properly, it should run WOT at 5500-6000.) Needless to say I left it connected to the internal source on my first trip back, and about an hour into it it started struggling again, then would run absolutely horrible under load(would'nt even get on plane) Thats when I went home and connected the external tank, still no joy. So I am going to check the items you guys suggest and run some injector cleaner through the system, hopefully I 'll be back in business. I am getting a real itch to catch some fish.
Thanks again

 

[flatsprowler]

Re: No power under load? Anyone?

They said the compression was fine, but I think, like rodbolt says, i need to check these guys qualifications.
I bought the repair and maintenance manual for my engine, maybe I should just study this and be my own mechanic, seems finding a quality boat mechanic is tough work.
Thanks guys, I am going to mess with this thing heavily this weekend
I'll let you know how it goes doing the items you both suggest

 

[Woodnaut]

Re: No power under load? Anyone?

Flats - I had an unusual situation last year that ultimately occurred as a result of water getting into the gas. I have an 2006 F90. Here were the symptoms: The engine would run perfectly at idle or under no load. Put it in gear and try to get up on a plane just fine, however, and the engine would start cutting out and running horribly after just a few seconds. I mean really horrible.

The cause was a plugged inline fuel filter - the one on the engine between the low pressure fuel pump and the VST. The net result was that fuel flow into the VST was just a trickle of what it should normally be. At idle - or no load - the VST would gradually fill up and everything would be just fine. With enough throttle to get her up on a plane, however, the fuel was leaving the VST faster than it was going in. After just a few seconds, it would practically run out of fuel and dog out.

I pulled the little fuel filter out of the line, pumped some clean gas backwards through it and a buch of gunk came squirting out. I cleaned it out as good as I could and then reinstalled it. I immediately had my good old engine back again.

The gunk was ultimately caused from water in the (ethanol based) gas. I had gotten a pretty good slug in the tank and it made a real mess of things. Needless to say I keep a pretty good eye on my fuel, and all of the fuel filters. Hope this is of some help to you. - Woodnaut

 

[rodbolt]

Re: No power under load? Anyone?

DO NOT run injector cleaner in it, it will most likly burn a valve long before the clener can work.
at 4000 RPM max it was not fixed.
I cant remember the test wheel number,its something like YB1626.
now your faced with finding the reason the fuel isnt in the intake tract, could be a filter in the hull,if there actually is one. if not 50 lashes.
could be the filter between the lift pump and VST,if its there.
most likly will be the filter in the VST and injector screens.
systematic testing will quickly resolve the problem. takes about 1.5 hours to clean the VST on an F115.

 

[flatsprowler]

Re: No power under load? Anyone?

Woodnaut, Rodbolt,

Thanks for the additional info. I will check all these things out and not run the injector cleaner through it. Thanks for the heads up
Man, I ought to have this thing figured out in no time

 

[rodbolt]

Re: No power under load? Anyone?

trust me, it aint hard. if it was I could not do it.
if I can do it the monkeys in the trees watching me fish on Lake Guri can do it.
but the Mackaws could prolly speak better