Loss of RPM at full speed

[skeeterronnie]

I have a Yamaha 225hp / 3.1L engine on my boat and it has plenty of power out of the hole but loses power and RPM after about 200 yards of running. Starts out at about 62 mph and dropes to about 48 to 49 mph.

I have put a portable fuel tank on the boat and hooked it up to the fuel filter on the engine and the boat did the same thing. I then changed out the fuel filter still the same, I then changed out all three of the fuel pumps on the side of the engine still the same. I cannot find any fuel leaks on the engine. The fuel bulb will pump up and get hard but will not hold the pressure for over a few minutes even if the engine is not running.

Iam lost as to what to do next. Could it be a coil, but the fuel bulb does not hold pressure.??????????

 

[skeeterronnie]

Re: Loss of RPM at full speed

Sorry the motor is a 2001 model 225 hp 3.1L engine and it has an oxygen sensor and I have cleaned the sensor and de carboned the engine also.

 

[ARCHSEA BUNKER]

Re: Loss of RPM at full speed

Try vst tank filter

 

[rodbolt]

Re: Loss of RPM at full speed

well
well
its like pulling kids teeth.
dunno why but most customers like paying me to guess and find their lies.
would a FULL model number be so damn difficult?
now we know we are dealing with at least one of about 4 Ox66 systems.
do you understand waht the primer bulb does and why its even there?
key word HINT, its a PRIMER.

 

[skeeterronnie]

Re: Loss of RPM at full speed

Sorry rodbolt this was not intentional at all ,but the motor is a 2001 Yamaha 225 3.1L Vx225 TLRZ Fuel injected OX66 manufactured 7/2000. This was everything I could find, hope this helps.

 

[rodbolt]

Re: Loss of RPM at full speed

ok
its a VX,different ign system than an SX.
the fuel primer is just that,it primes the system. once primed its not needed and as its on the suction side it cant stay hard.
your describing a lack of fuel pressure,most likly a clogged VST filter.
the VST tank can be removed without removing any fuel lines.
remove all the screws you can get to,then remove the 3 bolts holding the tank to the block. then remove the last two tank screws and the tank will drop away,twist the filter and pull down.
if the VST oring isnt damaged it can be reused.
the filter can be cleaned if its not damaged.
takes about 30 minutes.

 

[skeeterronnie]

Re: Loss of RPM at full speed

Ok RodBolt I removed the VST filter and cleaned it out. Finally got to try out the boat again it does the same thing. It will come out of the hole great and will run up to 5200 RPM then after about 5 seconds it will ease back to 4500 RPM for a few seconds then back to 3800 RPM. Holding the boat wide open it will hold 3800 RPM for about 10 seconds then it will ease back to 4500 RPM for about 3 seconds then take off and go bact to 5200 RPM. Then repeat itself. Could this still be a fuel pressure problem and where do I go next..

Thanks in advance

 

[skeeterronnie]

Re: Loss of RPM at full speed

hey guys I hooked up a pressure gauge to the fuel line and the pressure is holding at 40 pounds now matter what I do. Could this be a injector problem. Where should I turn next. I am at wits end.

 

[skeeterronnie]

Re: Loss of RPM at full speed

Here is a list of what I have done so far on my 01-vx225 yamaha.
1. Changed out the fuel filter before the low pressure pumps
2. Put on a spare fuel tank and hooked it directly to the low pressure filter
3. Cleaned the o2 sensor
4. Replaced the spark plugs
5. Cleaned out the VST filter
6. Put a pressure gauge on the top side of the VSTank it helt 39 pounds of pressure no matter what I did.
7. Replaced all three low pressure pumps with new ones.

I have done all of these things and the motor still will run great to 5200 rpm and then will lose power all the way to 4000 rpm. Then after a while holding the throttle wide open it will go back to 5200 rpms. Then it will repeat itself.

Could this be injectors or is there something else I need to look for.

Thanks in advance

Could use a little help please.

 

[rodbolt]

Re: Loss of RPM at full speed

yes, you can remove and clean the injector filters or use the mercruiser filters from about a 2000 model MPI 7.4L
about 3.50 a piece.
you should also checkl fuel system vacum at the lowest lift pump intake should be less than 6" hg at WOT.

 

[smith009]

Re: Loss of RPM at full speed

It is very good information about Loss of RPM at full speed. It is very helpful and interesting for every one. Every one can share their thought about it. According to me i think that Loss of Power problem / MAF Sensor - Contamination could cause this. Fuel Pressure - Fuel pump problem? Engine Miss / Make sure the Timing Belt is in TIME! Correctly installed. Miss and Loss of Power could be cause by this.