2004 Yam 150 4 stroke problem

[flatbottom]

This is my neighbors boat. Long story short, this engine wont accelerate. I flushed the fuel system, checked the thermo switch, and the block temp sensor, gave it fresh fuel and when I try to accelerate, it stumbles, misses and backfires, it wont go on plane. When I back the throttle down from trying to make it go, it settles down to a pretty decent idle, after it's warm, it idles ok.

It stumbles and misses right out of the gate as well, when its not even warm, makes no difference, warm or cold.

This problem started when he towed someone out of some muck and pumped some muck through the engine. He said that the engine was still pumping fine but he replaced the pump anyway. He didn't hear any alarms.

At the time this problem started, he was running on the hull tank and has since gone to a 6 gallon above deck tank, all fuel supply/components are fresh and new.

When I started working on it, I drained a few ounces of water out of the filter bowl on the engine and cleaned everything up real well. Last time I ran it, I noticed that the bowl on the engine filter never gets completely full, its always stays a half inch below the top, is this normal?

I swear it sounds like it's starving for fuel, it pumps good out of the fuel rail (Schrader valve) but I haven't checked pressure yet.

I am starting to suspect the vct and possibly clogged injectors, a lot of work to get to it on these 150's.

Does this engine have any code that can be reset in the ecm that would send this thing into limp mode?

I'm at my wits end, Have I missed any thing simple here before I tear the fuel system down? This thing only has 100 hours on it, it's a shame to just let it sit there and rot.

Help please,

Thanks,

Scott

[fairdeal]

injectors sound like a good culprit to me also -

although it can't have anything to do with "muck through the engine"...



If you put a gauge on that Schraeder valve you should see it hit 45 psi at key on

then drop to ~38 while running.


Its normal for that on-board fuel filter to look "partly full".

Nothing to reset in the ECM.

If it only has 100 hours since 2004, it HAS been sitting there rotting...

so yes, it would be worthwhile to also open up the VST and examine that strainer

[pstephens46]

Fuel tank needs to be pumped and cleaned. Matter of fact cleaned from tank to injectors. Injectors will just re-clog after 10 YEARS of nasty fuel sitting around...

[tarheel53]

Sounds exactly like my F150 problems last spring. Changed all filters, including the VST - had injectors serviced - problem solved.

The VST is not that bad a job - I'd never done it before - took about 3 hours including fumbling around through inexperience. Be sure to take note of all the electrical connections you un-plug - easy to miss one putting it back together.

JB

[pstephens46]

Do it right the first time or just keep doing it....

[flatbottom]

Thanks everyone for such quick responses, such a ton of experience on this board.

I guess while I am in there, I should look into the 2 manual fuel pumps that sit on the cylinder head as well. I assume these supply fuel to the vct, for the HP pump contained therein, correct? Are there any tricks to these 2 pumps on the head? Can I just take them apart and clean them out?

Guess I should replace all seals with new when I am in there.

Also, as I follow the fuel path in the Yamaha manual, I see that there is an inline filter (#3 in the manual) between the 2 pumps on the back and what I assume to be the supply for the vct. Along with the screen in the vct, this filter, if it has one, (surprised I didn't see it on the engine when I was poking around under the covers) also needs to be changed.

I'll also be recommending a REAL filter for this thing, much before the engine, like a 10 micron Racor? Suggestions?

Thanks again, I'll post back when I have results.

Scott

[tarheel53]

Agree - not suggesting that you limit your efforts to the filters.

[cpostis]

At the time this problem started, he was running on the hull tank and has since gone to a 6 gallon above deck tank, all fuel supply/components are fresh and new.

Didn't mean to have a lengthy post, but it did get a little drawn out.

Here goes...

I bought my 1991 boat/2001 motor for a song after the real estate crash. I did not run a sea trial. When I went to pick the boat up, the seller had told me he filled the 70 gallon tank up with what kind of fuel, I didn't know. I thought, why if he was struggling he would do such.

Dropped her in the water in a canal and did a minimum "sea trial". no problems yet. First time I ran her for a good run, I could not get her over 3,400 rpm consistently.

So I started checking/cleaning the fuel system. Minimal water in the fuel/water filter/separator, no water in the engine fuel filter with what looked to be good clean fuel, but white powdery substance clogging the VST HP pump filter. I removed the access panel and the fuel sender plate on the fuel tank, inspected the tank. It was like looking in a mirror, good clear clean fuel, no deposits in the bottom. I did drain the tank with a pump through a filter, recirculated through the filter for hours, and reserved the fuel for other equipment. I filled the tank with REC 90 fuel.

So out I went with great runs reaching max RPM for several trips. Then after a few of those trips had the same problem, not consistently over 3,400 rpm. I pulled the VST and found the filter clogged again with white powdery substance.

What I didn't do on my first inspection was check my fuel line from fuel tank to fuel/water filter/separator. I found the inner liner not the white translucent appearance it should be. It was very white chalky, and I could scrape that "chalk" off the inner liner with a pick. Some boat owners have had their non-ethanol safe fuel lines turn brown and break apart into "chips". Not in my case.

I suspected it was from effect of ethanol blend fuel. Although I now only use REC 90 non-ethanol fuel, I replaced with good quality marine "ethanol safe" fuel line. Never had a fuel issue since, knock on fiberglass!!

My point is, as others have said ,check all possibilities. In the long run you will feel confident that the problem is solved.

If you are still testing/running with the 6 gallon above deck portable tank and think you have the problem licked, you might want to reconsider.

Of course, you may have other than fuel issues?

How nice you are to help your neighbor!!!

Good luck!!!

[cpostis]

This may help with VST access .

F150 VST filter replacement - The Hull Truth - Boating and Fishing Forum

[pstephens46]

This may help with VST access .

F150 VST filter replacement - The Hull Truth - Boating and Fishing Forum

Good stuff. Thanks for posting. Planning on digging into mine this fall/winter.


There is another fuel filter in addition to the hp pump filter. Fairdeal refers to it as the F shaped filter. Located in-line above ST. What is the opinion of the forum about replacing this one? I scanned the link above and did not see it mentioned.

Also heard from several that the hp pump filter can simply be cleaned versus replacing......

[fairdeal]

The Yamaha VST "filter" is - by my definition - a single layer of "woven screen"

and IMHO eminently cleanable with a toothbrush and perhaps suitable solvent / surfactant.

The "F filter" and its variations - located between the lift pump and VST - are also "screens" -

but as they are encapsulated in a plastic housing, cleaning them would require a miniaturized Raquel Welch...

[TownsendsFJR1300]

Drain the VST, (there's a small screw at the base and hose) and catch what comes out in a CLEAN CAN. Debis, water, etc, will show.

You can also pump the primer bulb to flush as well. Blowing back gently into that drain may also loosen any crap at the bottom of the VST.

Its costs nothing but some time and will give you an idea how deep you have to go.

Plus 1 on checking fuel lines for internal breaking down. Re-powered in 2007, the line between the transom filter and under hood of my F150, I found the inside of that fuel line came loose and the Yamaha filter caught it.

Re the transom filter, a 10 micron is the standard. I put the one with the clear cup at the bottom so you can SEE AND DRAIN all water before it gets to the engine..

[pstephens46]

Yep Townsend. I have done all that. If I can get to the other two filters I believe I can then say "all filters have been serviced" Curious also to have a look at the VST and filter as I am the third owner. Bout a 100% chance one of the other yahoos burned ethanol for a while.

I like Raquel Welch full size...

[rodbolt17]

VST and injector service takes about 1.5 hrs.

sometimes the HP screen deteriorates.
sometimes the VST seal swells on removal.
IF the lift pump screws come out it takes about 15 min each to replace the diaphrams.

as it is such an old motor it is unlikely the latest link and sync has been done.
if it has not it may tend to stumble and stall at low speed throttle movement.

[flatbottom]

Thanks for all the great help guys, I am just starting to get to this project.

Question: Do the grey fuel lines used on this engine stand up to ethanol blended fuels? Or should I change them all out when I am doing everything else?

Also, where do you guys send your injectors to get them cleaned/serviced?

Thanks,

Scott