04 f-150 losing RPM and speed at full throttle

[danielreilly09]

Boat started having problems on a trip I had last month. It's an 04 on a 185 G3. The motor has less than 70 hours on it. If The throttle is put all the way down it was going up to normal RPMs. If the throttle is left down the boat will lose RPMs as well as speed. If you ease off the throttle for a second and then push it back down, the RPMs momentarily go back to the higher RPMs and then decrease just the same.

Had the boat in for just over three weeks now. They say it's dropping a cylinder but they're not sure why. No codes are coming up. They've replaced gas filter, spark plugs, and fuel injector and nothing is seeming to work. They also tried a different prop since the prop that came on the boat was not correct. They have no idea what is causing this.

[99yam40]

Are these Yamaha people working on it?

Monitoring fuel pressure at problem RPM should tell if there is some kind of fuel supply problem, but will not show injector problem.

They should be able to monitor peak voltages to coils also to see if dropping spark

[danielreilly09]

They're factory certified mechanics...... Not many of them in the Milwaukee area. All of the pressures are coming back with good readings. As well as every other test

[99yam40]

may need to find a Yamaha master tech to look at it, computer does not give all the answers
If tests have been done and everything is in spec we will not be able to give a magic answer as we do not know what tests have been done and what the results were

Let us know what they find out

[danielreilly09]

I looked on the website and there is not any master techs in the area..... Or the state for that matter. Also, the motor is out of warranty date even though it only has 70 hours on it

[rodbolt17]

your describing a typical VST filter clogging.
rail pressures MUST be checked at the PROBLEM RPM.
sitting on a flusher the numbers are useless.
clean the VST filter and spray out the injector filters.
not hard,takes about 2 hours.
remember to change the VST pre-filter as well.

[danielreilly09]

I just talked to the mechanic and shared what you suggested. He said they had checked this. The VST filter was clean and they blew it out anyways. They also replaced the pre filter. He said he had spoken to one of the Yamaha techs and he was going to check some filter above the VST filter as the next step. They had tested the pressure at the RPMs and the pressure was within normal ranges. I dont know the numbers but this is what they said

[99yam40]

really hard to believe that fuel pressure is not dropping when problem is happening.

Could it be that they are not testing under load at WOT where the problem occurs according to you

[danielreilly09]

All I can do is go off what they're telling me. I think that's part of the reason they're so stumped. I'm just trying to find out whatever I can and talk to whoever I can to get some help.

[danielreilly09]

Just talked to them and they are ordering some filter that is right before the VST. This is coming from one of the techs at Yamaha that they are working with. Does this sound like it may be right?

[rodbolt17]

sounds like one of two troubleshooting methods are being used.
either the splatter gun or the poke-n-hope method.
neither are very good.
if it is a pre filter than rail pressure would drop at the problem rpm and load,
if they are testing on a flusher ALL pressure values are a teat on a boar hog.

[danielreilly09]

According to them the pressure is within range..... I'm not sure what the range is. They got the fuel filter that I guess is before the VST and are trying it out tomorrow. I know they are testing it on the water and not in the tank at the shop. Hoping that this fixes it but I'm thinking that it probably won't.

Not really sure what I should be doing. The motor is out of warranty but it has less than 70 hours on it. I have talked to Yamaha and I know they are as well but it's been over a month. Just bought the boat as a graduation present this spring and it's been in the shop all summer. Should I take it to a different shop? There are no master techs in Wisconsin. The Milwaukee area does not have a ton of factory certified mechanics and this is one of them. Looking for suggestions

[99yam40]

If it was a filter plugging it would show up in pressure test.

It is tough to troubleshoot without knowing the numbers, and the difference of them when running properly and when problem shows up

[danielreilly09]

Well the filter they just replaced did not fix the problem. I agree that if the fuel was being restricted it should show up on a pressure test. I am going to get a copy of all of their numbers do I can post them. Yamaha said the next option is to try balancing something. I'm not sure what it is called

[rodbolt17]

they are using the splatter gun method, with about the same results as the poke-n-hope method.
once you get the surging issue resolved you nost likely will have to replace the balancer assy.
all the f150 motors i ever saw,including my 07, made before 08 have had balancer failures.
at least the balancer went down to about 330 dollars.