Losing Power At High RPM

[DennisG01]

Hi all, I'm wondering if any of this seems familiar to anyone or any recommendations on places to start looking... or a direction to look in...

-- 2001 SX250HP OX66.

Problem:

-- Can run all day long at mid 3,000RPM to low 4,000 RPM range with no issues. Engine runs like a champ.
-- When going WOT, after 10 to 30 seconds, it will start to lose power - and it loses power rather quickly
-- If I back off to a lower RPM range, all is fine
-- If I hold the higher RPM, power will continue to drop lower and lower
-- I did not try holding the throttle handle WOT so long as to see if it would eventually stall out

Notes:
-- Fuel is clean (use Startron and RingFree religiously). Collected fuel from the VST drain and it was clean/good.
-- VST hi-pressure pump filter is clean
-- Spark plugs appear all similar in color - dark brown, slightly black
-- Fuel injectors were professionally cleaned less than 100 hours ago.

It will be about a month till I get back to the boat, but was hoping to get some recommedations?

-- I plan on running with a fuel pressure gauge hooked up to start with... Trying to narrow things down.

[99yam40]

monitoring rail pressure to see if that is dropping is a good idea.

shutting off the key a soon as the problem shows up and seeing how much fuel is left in the VST is another.
but would be a pain on the water I am sure
sucking air or recycling too much fuel to keep VST filled might be your problem, if rail pressure is dropping.

[mjm-1957]

. Another possibility could be a restricted or clogged vent. Try loosening the gas cap when this happens.Is the primer bulb collapsing?

[99yam40]

. Another possibility could be a restricted or clogged vent. Try loosening the gas cap when this happens.Is the primer bulb collapsing?

good thought, but I would think a plugged vent would affect the motor at lower RPMS also not just WOT.

also does pumping the primer bulb help while the problem shows up.
if sucking air into the line after the primer, the positive pressure from pumping the bulb might help

[DennisG01]

I would "think" that a clogged vent would cause issues at other times. The engine is as strong as usual getting onto plane - no loss of power there. But still a good idea - I welcome them all!

I forgot to mention that I also have a vacuum gauge on my filter head - so I know the filter isn't clogged based on the vac gauge.

I also forgot to mention that we did try pumping the fuel bulb while the issue started to present itself - no change. Thanks for mentioning that!

If fuel pressure drops - I'll check the quantity of fuel in the VST tank. Good idea.

[Capt. Ed]

I too have had the a very similar issue with my FX225s, it will alternate engines, even when on two independent fuel supplies. I have throttle down, and slow increase, but as I near 2000 to 2500 it will start to run rough, after a while it will increase and run fine... then the other one will do it. New YST pumps, filters. And fuel pumps. Ball makes no difference, inline long Yami filters 10 mc.

[DennisG01]

I too have had the a very similar issue with my FX225s, it will alternate engines, even when on two independent fuel supplies. I have throttle down, and slow increase, but as I near 2000 to 2500 it will start to run rough, after a while it will increase and run fine... then the other one will do it. New YST pumps, filters. And fuel pumps. Ball makes no difference, inline long Yami filters 10 mc.

Thank you, Ed, for joining in. But please start a thread for yourself so as not to derail this one.

[oldmako69]

My 225s would do this all the time. The Fuel Injection rail returns fuel to the VST. Ethanol would slowly rot away the innards of the fuel line loop from the output port on the VST, to the injectors and then back to the VST. TINY bit of rubber would slough off the hose and enter the VST. The screen on the bottom of the HP pump would clog just a bit. Low RPM ops, fine. WOT, no good.

It was either the above or the injectors were dirty. I realize you checked the filter and rebuilt the injectors, but in 100 hours of operation, my engines could dream up ALL kinds of ways to ruin my day on the water.

I ended up replacing ALL the fuel lines because of E10 rot. Cut the small ones in the loop lengthwise and opened them up. They were falling apart internally. That crap was then clogging the screen and the injectors.

Good luck with the fix.

[DennisG01]

My 225s would do this all the time. The Fuel Injection rail returns fuel to the VST. Ethanol would slowly rot away the innards of the fuel line loop from the output port on the VST, to the injectors and then back to the VST. TINY bit of rubber would slough off the hose and enter the VST. The screen on the bottom of the HP pump would clog just a bit. Low RPM ops, fine. WOT, no good.

It was either the above or the injectors were dirty. I realize you checked the filter and rebuilt the injectors, but in 100 hours of operation, my engines could dream up ALL kinds of ways to ruin my day on the water.

I ended up replacing ALL the fuel lines because of E10 rot. Cut the small ones in the loop lengthwise and opened them up. They were falling apart internally. That crap was then clogging the screen and the injectors.

Good luck with the fix.

Thanks, Mako. When I took the VST filter off, I was HOPING to see it clogged... but it really wasn't. Just a tiny bit of whitish material, which I believe is somewhat normal - some type of degradation of the aluminum, I think. But it was nowhere near enough to cause the problem - and once I cleaned it, the problem was still there.

I'll know more at the end of the month when I get a chance to put a fuel pressure gauge on it. That will at least start to narrow down my possibilities.

[DennisG01]

Ran the boat today with a fuel pressure gauge hooked up.

-- Fuel pressure went right to about 34psi at idle and did not waiver all the way up to about 4,300RPM's.
-- Went WOT and the pressure started to smoothly drop (over the course of about 5 seconds) to about 29psi. Then it jump instantly to about 20psi and the engine started to complain. Kept it at WOT for a few more seconds and the needle started acting erractically and the engine complained big time, starting to die.
-- Pulled the throttle back to neutral and the engine smoothed out.
-- Ran about 3,800RPM for a few minutes till I got back to the dock with no issues.

Must be a fuel issue and NOT electrical, right?

? If the fuel pressure regulator was bad... would that exhibit problems at ALL RPM's?

I'll check tomorrow to see if I have my Mity Vac pressure/vacuum tool and will check the LP pumps. I may have left it back in PA (I'm in ME right now).

Other thoughts?

[99yam40]

is the VST staying full at high RPM.
if it gets low due to not enough fuel in the VST the pump cannot pump what is not in there

[DennisG01]

is the VST staying full at high RPM.
if it gets low due to not enough fuel in the VST the pump cannot pump what is not in there

That's kind of what I'm wondering (low pressure pumps).

But, how can one check that? I can drain the fuel in the VST after just idling. But the level is going to vary based on whether it just filled or was getting close to being filled (float position). And how would I drain the VST after running WOT? I have to throttle back to stop the boat... which means the VST tank will fill up again.

With all of those variables, how can the amount of fuel in the VST tank be accurately measured? I must be missing something - how would you do it?

[99yam40]

I would think turning the key to the off position when the problem shows up at high RPM, would stop the lift pumps from filling

[DennisG01]

I would think turning the key to the off position when the problem shows up at high RPM, would stop the lift pumps from filling

It seems weird (not a good idea) to do that at 40MPH? But I suppose there's nothing really "bad" about doing that? Maybe just toss it into neutral right away? Maybe I'm overthinking this one, too...

[DennisG01]

Didn't have a whole lot of time for "fun" today...

The only thing I got accomplished was loosening the low pressure pumps from the block and squeezing the primer bulb to see if they were leaking, which they were not.

I didn't bring my MityVac with me to test them for pressure or vacuum, but apparently that little test above is a decent "quick and dirty" test.

If I have time tomorrow, I'll try collecting the gas from the VST after idling and after the engine shuts down from a WOT run.



Anybody with thoughts on my question about the fuel pressure regulator above?

Also, am I correct in assuming that if the HP pump was failing, it would be failing at all RPM's?