2004 Yamaha 150 4-stroke RPM/bogging down problem

[joshkent]

My 2004 Yamaha 150 was good to go when I bought it used earlier this year(165 hours). Now, it has steadily lost power/RPM's over the last month or so. When the throttle is at max the RPM's increase for a second or two then the motor just backs down to about 2500 or so (the tach is inop so I'm guessing there). When it is out of the water it runs great while running fresh water through it. I beach the boat often and think that might be causing it because when I run fresh water through it after use it seems to do better until the next time I beach it. Is there a filter somewhere in the lower unit that may be getting full of sand or mud that I can change? Any help would be much appreciated!

 

[BaileysBoat]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

That is an EFI engine. I hope you have a 10 micron water separating fuel filter upstream of the motor.

I would start by ensuring clean fuel and checking the underhood fuel filter. Then get a manual

 

[Shermanator31660]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

Check the factory water/fuel filter separator that on the front of the engine and see if there any water or gukk in it. For sure, as BaileyBoat said, I'd be putting in a proper water\fuel separator as well. I put one in my boat and run the big motor and kicker through the aftermarket filter, never had a problem. I don't think beaching your boat will do anything unless you've run the leg through the mud and its plugged the screen and then your motor is over heating and shutting down. However, if thats the case you've probably burnt out the impeller in the water pump by now. The only screen on the lower leg is removed with one bolt, that's it, so make sure you get your leg up before you beach the boat. There are quite a few filters on this motor, not just the fuel filter itself, but I'd start with the main stuff first..... Sherm

 

[joshkent]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

I replaced the filter on the front of the motor but no joy there. I can't find another fuel/water separator, is it possible the boat (2005 Hurricane GS202) wasn't outfitted with one originally? Seems strange to me that it wouldn't have one but I've looked everywhere and can't locate it. Thanks again for the help.

 

[99yam40]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

Test alarm systems to see if they function properly.
You could be getting an oil level or overheat alarm but buzzer is bot sounding.
The motor will go into a reduced RPM mode when alarm comes in.

If it has been having problems for a month and you kept running it you could have already hurt the motor.
Take it to a good Yamaha shop and have it checked out by a trained Yamaha Tech
These newer motors need the proper equipment to check them out properly, just like the modern autos

 

[joshkent]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

I don't know if the boat has an alarm system (I've not heard an alarm as of yet nor do know how to test it if it does exist) but the oil level is good to go. I could get the boat to go pretty well when I would back off and push the throttle every 3 seconds or so, but I'm thinking that's bad now that I read that last post! It's like the motor is starving for gas no matter what I do with the throttle. Frustrating.

 

[junkyardwarrior]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

What you're describing is almost classic symptom of VST pump and/or filter failure. Also the injectors have tiny screens in the top of them that can clog. If they clog, the injectors need replacing.

I've done a few 115's and one F150. It's an expensive job. A 10 micron filter would solve it by way of prevention. Usually what I'm seeing is poor fuel quality. That and boats tend to sit around a lot, and because of that the fuel degrades...fast. When degraded fuel is run through the VST filter and pump, it can (and does) take out the pump, the filter, and occasionally the injectors.

 

[joshkent]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

I cleaned the injectors and that wasn't it. The gas is all new so that's not it either. One thing I did notice was the fuel bulb would not pressurize the system even with the motor off, could that be something in the fuel tank or possibly clogging the fuel lines before the gas even gets to the motor? When I start the motor, the fuel barely goes through the 10 micron filter I just replaced, and that was after I bled the system at the fuel rail.

 

[joshkent]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

I pulled the VST out and it was clean also. Is there a way to test the fuel pump so I don't have to buy a new one?

 

[BaileysBoat]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

I cleaned the injectors and that wasn't it. The gas is all new so that's not it either. One thing I did notice was the fuel bulb would not pressurize the system even with the motor off, could that be something in the fuel tank or possibly clogging the fuel lines before the gas even gets to the motor? When I start the motor, the fuel barely goes through the 10 micron filter I just replaced, and that was after I bled the system at the fuel rail.

It's not difficult to test the supply hose-disconnect the fuel line after the bulb and see if it will pump fuel into a pail. Primer bulb should be vertical.

 

[BaileysBoat]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

There are quite a few filters on this motor, not just the fuel filter itself, but I'd start with the main stuff first..... Sherm

You need to verify the filters as stated. One in the VST and one between the LP pumps and the VST.

 

[99yam40]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

monitoring fuel pressures should tell you if there is a restriction and where

 

[joshkent]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

I tore apart the whole intake manifold to inspect the VST and all looked super clean (VST and LP Fuel pump filters, too). It still has the bogging down just as before and now the idle is way too high.

 

[BaileysBoat]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

monitoring fuel pressures should tell you if there is a restriction and where

What is your fuel pressure? High idle could be a vacuum leak or idle speed control-when you shut down the ISC should
"rattle" for a few seconds as it re-sets.

The throttle position sensor should be checked. You will need a test harness or a laptop with YDS.

 

[Thfrazer]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

Amazing! I have a 2004 GS 202 with a 2004 Y150F doing the exact same thing. The rpm was good when I bough it used, but now it has dwindled down to a max of about 4000rpm. If I play with the throttle I can get it up a bit to 4200-4300rpm, but that is it. I've replaced the plugs to no avail.

I'm thinking it has to do with the fuel tank/line/pressure somehow. My next attempt is to get a spare tank and run it from there to see what happens.


Thanks,

Tom

What is your fuel pressure? High idle could be a vacuum leak or idle speed control-when you shut down the ISC should
"rattle" for a few seconds as it re-sets.

The throttle position sensor should be checked. You will need a test harness or a laptop with YDS.

 

[joshkent]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

Figured out the idle problem, an intake manifold packing fell off during installation. When I fixed that and ran the boat it started off great and got right up on plane but slowly (after 30 seconds or so) backed off to 2500 RPM's again. Basically, right where I started. Do the low pressure pumps work in tandem or separate? That seems to be my last resort after I bypass my fuel tank on the next run later today like the last post mentioned.

 

[schematic]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

You are simply spinning your wheels until you verify fuel rail pressure while under load. Until you do that, you are shooting in the dark....

 

[joshkent]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

Good point about the pressure, I haven't done that yet. I tried an alternate gas tank and it did the same as before. Also, when I removed the inlet hoses of the low pressure pumps I had no suction. I bled the lines and it got a bit better but still doesn't feel right because it surges. Is that normal?

 

[joshkent]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

Figured it out, it was the injectors. When I cleaned them I only pushed fuel injector cleaner through them as the flow normally goes through. This time, after reading another forum about this, I reversed the flow and 2 of the injectors "popped" and the fluid flow improved dramatically. The boat ran better than ever after that...right until the prop fell off. Yikes. I would like to thank everyone who offered advice, I learned a TON of great information about my engine and it was all from here.

 

[phallgtown]

Re: 2004 Yamaha 150 4-stroke RPM/bogging down problem

I have been having a similar problem, I dont have a lot of time to do my own work and not really expereince with outboards. My motor starts and idles no problem, ball me seem a little soft and I can pump it up. What i have noticed is under load WOT the fuel in the filter quickly drops to the bottom of the filter element and the only way to get it to recover is to pump the ball.
Did you notice this issue with your fuel filter prior to cleaning the injectors.
How much work is it to clean the injectors? Maybe I need to buy a manual and try it myself