Shipyard Isl. Marine Engine Parts - Yam f115 - fuel restriction? or lp fuel pump failure?

I have a 03 f115 yammie.

The fuel filter before the low pressure fuel pump keeps running low. I can fill the filter bowl with gas by squeezing the primer bulb. When I run the motor, I see the gas level dropping slowly. It will drop to the lower edge of the fuel filter. At first I thought it was a fuel restriction before the filter. But when open the fuel filter, gas starts to gush into the filter bowl.

Could the low pressure pump be not working?
Or a possible fuel restriction after the fuel filter?

Note - the fuel filter and fuel filter assembly is new. The fuel assembly cracked for some reason.

Any help is greatly appreciated. :tht_rulez:

Sonny

Sonny,

How does it run otherwise?

Andy

I'm a newb at boating and the motor is also new to me with approx 750hrs. However, to me, it seems to be running a little rough. It's mounted on a 19' glasspro (Hawaii made boat). At WOT, the highest rpm I got it to was about...5k. Most times it'll hover around 4.5k rpm and go up and down. My first thoughts were an overpropped motor. I replaced the yamaha 17p stainless prop with a vortex (I think) 15p aluminum prop. No change in rpm. I'm thinking that I have a sick motor.

I was planning to change the spark plugs and clean the fuel injectors. At his point I'm jus trying to figure out why the gas is dropping in the filter bowl. Then work my way forward from there.



I already checked and cleaned the vst tank and filter. I didn't see any trash in the vst tank/filter.

There is a similar post to yours running right now. One thought is the low pressure pump. Also, a rebuilder has said the Yamaha F115 gets the injectors pretty dirty,. and he can clean them for $20 each. But he is in NY...

Triumphrick.... Interesting you say that. I'm currently in washington dc visiting my Sis. We're heading to NYC on Monday. However the injectors are at home (in warm weather). I was thinking of bringing the injectors with me but I didn't think I would have time to clean the injectors.

I figured that I could get some information on what's wrong while I'm on vac.

Could you post a link to the other thread?

Answering your question on the fuel filter on the engine, it is normal for that level to fluctuate when the engine is running. If the low pressure pump is sucking fuel, that negative pressure can cause that level to lower.

Pump the bulb as hard as you can with the engine off. Any fuel leaking around the cup where it meets the base? Any kind of fuel leak by doing this will be a air leak when the engine is running.

Couple ways to troubleshoot the low pressure fuel pump. You could check out the pump output pressure with the engine running with a gauge. Or, run the engine at WOT speeds and have a buddy pump that primer bulb while its running at WOT. The bulb will not get firm, but are there any increases in rpm with bulb pumping? Is the bulb sucked in at WOT?

750 hours....your not wasting money having the injectors cleaned. I would also clean the rest of the fuel system. Check the VST inlet needle, and make sure that's clean. VST filter. Injector rail.

How does it run otherwise? Idle smooth? Any sputtering or backfiring on hard acceleration?

Andy

Thanks Andy!

Last time I went WOT, the bulb did not get sucked flat.
Ill get a fuel gauge to test the lp fuel pump. This way, I can test the pressure at the fuel rail also. Is there a special adapter to connect the gauge to the fuel rail?... Would a fuel gauge from the auto parts store work?

Cleaning the entire fuel system sounds like a great idea.

When the motor is in the water... I think it runs fairly smooth. Then again, I probably wasn't paying close attention to it. On the muffs, it sounds a little ruff.... But I think that's because of the lack of back pressure at the exhaust. But what do I know about outboards? Lol. I'll have to check if it sputters or backfires during hard acceleration.

Wont get back home until December. Again, thanks for your advice. I'll get back to you when I get to run some tests.

If your fuel rail is like mine the schrader valve is smaller then the style used on automobiles.

Finally got a chance to do some testing.

With the engine off... squeezing the bulb did not show any signs of a fuel leak at the fuel filter and through out the fuel system.
At WOT... squeezing the bulb did not produce more RPMs, nor did the bulb get sucked flat.
Idle does seem rough and there are no noticeable backfiring.

Using a fuel pressure tester....
- at idle, the lp fuel pump produced 10psi
- with the engive off, key on, the fuel rail produced 10psi
- at idle, the fuel rail produced 40 psi
at both locations the pressure held steady as i reved the engine. However, sometimes when I reved it hard, it would sputter and hessistate. Then it would recover a few seconds later.
(Note: the fuel tester I bought did come with an adapter that fit on the f115's fuel rail)

I did other tests as follows.....
- I pulled the plug for each spark plug, one by one.....
#1: dropped rpm
#2: stalled the engine
#3: dropped rpm
#4: dropped rpm (atleast thats what I think.... those sparks are damn scary!)
- I unplugged the fuel injectors, one by one.....
#1: dropped rpm
#2: big drop in rpm... nearly stalling the engine
#3: droppepd rpm
#4: no change in rpm

I didnt get a chance to inspect the spark plugs but I do think #4 is not firing and is probably a bad injector.

Does this sound like a logical assessment? ;?

just wanted to post an update.

i pulled the spark plugs.... #1,2 and 3 has nice even wear.... but #4 did not (dammit :mad: ). i thought.... maybe just a bad plug. started replacing the plugs.... when i got to plug #4, i thought about checking the compression. dang :banghead: .... i didnt want to take out the other 3 plugs so i only test #4 cylinder. pressure was on the low side but still above the minimum, so that should be good. placed a new plug in #4. fired her up..... still the same results. ;?

instead of sending my injectors for cleaning... i opted to buy rebuilt injectors, which ended up costing nearly the same as the injector cleaning service. :roll
dropped in the rebuilt injectors and fired her up. at idle they seem to run similar. however, when i punch the idle.... she reved up with ease. i pulled out the #4 injector connector.... she bogged down and dropped idle. thats a good sign... previously (with old injectors), there was no change when i unplugged #4 injector.

i'll be dropping the boat into the water this weekend. hope all is well. :rofl:

Sounds like it might be the problem! Let us know.

Andy

Took the boat out yesterday for a test run. As soon as we clear the harbor entrance, I punch it to WOT. RPM shot up to 4.8k and kept on climbing to 5.1k until I had to throttle down because of unfavorable sea conditions. I did several WOT and the difference is night and day. When conditions permit... I'll be checking my max RPM just to be sure it is propped appropriately.

As we continued to troll, I noticed that I can now keep a consistent RPM. Previously, going into head seas the RPM would drop as much as 1.5k which made it difficult to keep a consistent trolling speed. Yesterday it would fluctuate .1k only.

Next step is to send the injectors in for testing and cleaning. I'm interested to see what the test results are. Injectors will be kept as spare parts.

Andy - in a previous post you mentioned checking the vst inlet needle and injector rail. Do you still recommend I do this? Since my problem was a clogged injector, I'd like to make sure all components upstream of the injectors are operating as they should. With the fuel rail producing 40 psi.... I would guess vst is working fine. ;?

Mahalo,
Sonny

If the injectors had stuff in them, I would flush the entire fuel system from the VST to the rail.

Andy