Not getting full RPM?s on a F115

[rjpjr924]

Hi,

I am having a problem with a 2002 F115 (~ 400 hours) that is on an 1801 Century. I am not getting full RPM?s. It will only reach about 5,000-5,200 and does not seem to have full power. I have changed the prop from a 19K to a 17K, both which are the salt water series (did not make a difference). I have also checked and cleaned the VST tank, changed the fuel water separator filter, changed the impeller & thermostat, spark plugs, check fuel pressure (39 lbs) and did a leak down test (4%).

The only thing I did notice was that the plugs are a little black (running rich?). Any information or suggestions you could make as to what is going wrong would be greatly appreciated.

Thanks,
Bob

 

[BaileysBoat]

Re: Not getting full RPM?s on a F115

Is your boat heavy?

I think it's rated for a 150, so a 17p makes sense.

Was there no change in rpm at all when you switched props?

If the boat is lugging against a water soaked hull might see over fueling and black plugs.

 

[rjpjr924]

Re: Not getting full RPM?s on a F115

The boat is rated for 150hp, but there is a performance bulletin for Yamaha showing a f115 on the same boat and being capable of 6000 rpm and 40 mph.

My boat will only get to ~29 mph and ~5200 rpm.

The test weight in the bulletin states boat, motor, battery, safety and test gear and 45 gallons of fuel (2,698 lbs).

How do i tell if the hull is water soaked? The boat does not stay in the water it is trailered.

 

[John Doe]

Re: Not getting full RPM?s on a F115

Had/have same problem on 2001 F115 after about 300 hours and tried many of the same cures you thought ouf. My problem came on gradually until the boat almost would not plane. Broke down and took it to the shop in 2005 and they found a loose gromet in the electric fuel pump which resulted in crimped fuel line and restricted flow (sometimes 0 in the fuel rail). They reseated the gromet and put it back together. Supposed to have fixed it then but problem came back about a year later - same thing - gromet loose. Replaced gromet and am six months into that "fix" but engine still seems to be surging (Another problem you apparently don't have).

Hope this helps

 

[rodbolt]

Re: Not getting full RPM?s on a F115

this grommet I gotta see.
there is a rubber damper that contains a small filter on the pump intake and an oring on the pump outlet at the top of the vst.
no fuel lines internally in the vst.
shoot me a part number of said grommet if you can.

 

[Don S]

Re: Not getting full RPM?s on a F115

Could be talking about #9 in the picture below. It's called a grommet.

 

[rodbolt]

Re: Not getting full RPM?s on a F115

DonS
yep thats the part that couple the pump outlet to the VST outlet but it cant crimp a fuel line.
now if the ethanol melts it it can dump rail pressure.
never saw it but it could happen.
on the bottom of the pump,#8 there is a filter,damper and a cover.
the damper also helps hold the pump in place against the top of the VST.
if its missing or damaged it may let the pump chew up a grommet or fall away from it.
but once assembled correctly the damper rides in a machined area at the vst tank bottom and mashes the pump up and secure the pump in place.
its a joint between the pump outlet and the VST outlet pipe, if it leaks the pressure will spray inside the vst and rail pressure will suffer.
about the only way to correctly install the VST top to tank is hold the top upside down install the damper/filter and cover assy then with the other hand install the tank to the still upside down cover and then rotate it upright to install the screws.
otherwise the damper tends to fall off while trying to install it with the tank upright.

 

[Don S]

Re: Not getting full RPM?s on a F115

but it cant crimp a fuel line.

Agreed, but it sure could cut off the fuel supply if in wrong. Maybe his tech described the problem as being similar to crimping of a fuel line.

Here is a picture that shows the parts you are talking about for the filter.

 

[rodbolt]

Re: Not getting full RPM?s on a F115

yep thats the filter/damper assy,#7.
some programs and years its called a damper and some its a filter.
seems they changed translators a few times .
its simply impossible to install the grommet wrong. it just couples two nipples but if its damaged or the pump is loose cause the filter/damper assy is incorrectly installed or out of place it can dump rail pressure.
that damper assy sits at the tank bottom and holds the fuel pump up locking it into place.
draw back to it is it requires intake manifold removal to access the VST and then you have to remove the VST from the manifold.
with practice it can be done in about 1.5 hours.

 

[John Doe]

Re: Not getting full RPM?s on a F115

Thanks guys. I'm not a wrench, and you've explained it better than the shop has in two trips and $900. During the first visit they apparently reseated everything and put it back together. It worked OK for a year or so (30-40 hours) and then started acting up again. The second time at the shop they thought I had gotten into the fuel pump and messed it up. They subsequently replaced the "grommet" with OEM but not all is well after 6 months. I still get a surging at low rpm, but at least I get full rpms and top speed. Also, while at low rpm, the primer bulb is no full and if I prime it up the surge dissapates. Could this still be the HP pump not working properly? I've check the manual pump, no tears and in good condition as far as I can tell.

Thanks again.

 

[rodbolt]

Re: Not getting full RPM?s on a F115

now ya done gone and changed the symptoms again.
now at low speed your describing an air leak before the pump or a pump getting weak.
its normal to have to pump the primer bulb a few times its on the suction side.
as long as the bulb is not being sucked flat by the engine pump.

 

[John Doe]

Re: Not getting full RPM?s on a F115

Sorry man, this motor has had (and still has) it's share of problems and I'm only talking fuel delivery issues here and not recent voltage issues. Anyway, low rpm surging (and cutting out) and lack of top end rpm and speed use to to occur at the same time before the most recent grommet reset/replacement. Now I have top end rpm and speed but after running at high rpm and coming to idle, the engine surges by about 300-500 rpms. If I idle it for a couple of minutes or pump the bulb (it is not flat) the surge goes away pretty quick. I replaced the fuel line from the tank to water seperator and the primer bulb, but not the fuel line from the seperator to the engine. The fuel injectors have been checked and are within specs. The engine is almost 10 years old with 380 hours - it is probably is suffering sitting in the garage and not being run much. I can live with the surge so long as it doesn't progress to more HP fuel pump problems as has happened twice before. Any suggestions for a "next step"? Thanks again.

 

[mikeavionics]

Re: Not getting full RPM?s on a F115

Maybe not the same issue that you are having, but I figured I would let everyone know what happened with my 2002 F115 (not 100% sure of the year as the date is unreadable) on my 19' Sailfish that I recently bought.

I wasn't getting full RPM (maybe 5200 tops & 32 mph) with the 13x19 prop but it ran perfectly at lower speeds. I was thinking maybe it was over propped. I ordered a 13x17 and before I received it, the problem got worse. Next, I was in choppy water (probably had nothing to do with it) and I couldnt get it over 4400 RPM and after about 10 minutes of running, I was topping out at 4000 RMP and 25 mph. I pumped the fuel ball and it was fairly hard. I fished for about 4 hrs and it did the same thing on the way in. I ran around in calm water after sitting for about 1/2 hr and I was back up to about 5000 RPM. The next trip, it varied from 4200 to 4900. I read a million of these forums (thank you Rodbolt for a wealth of input / info!) and this is what fixed it...

I assumed that the 10 micron screen in the VST tank and / or the injectors were clogged. I pulled the intake to access the VST tank and cleaned some crap from the tank and the filter on the bottom of the pump in the tank. Then I blew out the injectors. Someone posted instructions for doing so and I guess it worked. I pulled the injectors out, clipped a 9v battery across the terminals, and blew the out backwards into a bowl with cleaner. I think it was called Mercury power shot. Be sure to wear goggles cause the stuff spews everywhere. And don't blow yourself up with the sparks from the battery once you have the cleaner all over. I took my sweet time to do everything and it took about 4 hrs. If I had to do it again, it would probably take no more than 2.5.

I took the boat out yesterday and its like a new motor. 5500 RPM and 40 mph. When I get my new prop, I hope to be right where I need to be. (5900 and better hole shot)
I noticed a screw on the bottom of the tank that is accessable without tearing anything apart. If it starts to show symptoms again, I expect that I may be able to flush the VST through that hole without pulling the intake.

I guess I could have stuck a fuel pressure gauge on the fuel rail and determined if I was losing pressure, but I didn't have one yet. I bought one ($10 at Harbor Freight) in case this didn't fix it but never had to use it.

Rodbolt... I assume you would suggest installing a 10 micron filter between the low pressure pump and the VST? I don't have one in there?

I hear they are trying to up the Ethanol to 15%. Assuming that contributed to my problems...That would suck.

 

[rodbolt]

Re: Not getting full RPM?s on a F115

yes install the 10 micron inline filter used on the F115 from about 05 or 06 and up.

on E15 it wont work.
so far there isnt a marine US market motor that can tolerate anything more than e-10.
heck my warrenty on my 08 ranger will be void with anything more than E-10.