200 HP OX66 Surges above 1700 Rpm

[mcbc10195]

I run a Marina in Lusby, MD but I do not get a lot of Yamaha work. I have a 200 HP OX66 that surges in power once you get it above 1700 Rpm's or so. It will drop down to around 1000 and then back up and keep doing that. I have replaced the O2 sensor and that did not fix it. I have run all of the fuel pressure tests and vaccum tests. The high pressure fuel pump operates at the correct pressure until it surges and then the gauge drops almost to zero and then as soon as it gains pressure the Rpm's come back up. There is only 1 hg of vacuum on the feed line and the low pressure pumps are working fine. The pressure regulator also tested ok. Does anyone know what would cause the high pressure fuel pump to lose pressure and then gain it back. Is it a bad pump, the filter on the pump, or maybe something electrical. Thanks for any help.<br />Justin

 

[BRIAN03]

Re: 200 HP OX66 Surges above 1700 Rpm

You need to check the fuel pressure from the low pressure fuel pumps. Make a tee and install it after the 3 low pressure fuel pumps. If the fuel pressure is steady. You need to pull the float chamber apart and check the fuel filter on the bottom of the high pressure fuel pump. You need the o ring kit to put it back together. If the filters clean I would make sure your not loosing the 12 volts to the high pressure pump(Blue and red) wire on top of the float chamber. If the 12 volts doesnt go away.You need a high pressure fuel pump. 780.00 list price. I would still check the all of the low pressure fuel pumps even if you need a high pressure fuel pump.

 

[rodbolt]

Re: 200 HP OX66 Surges above 1700 Rpm

hello<br /> check what brian o3 says. its classic the the low tech fuel pumps cannot supply the vst. also about 1800 rpm the high pressure pump swithces to a higher operating speed. its the way it was desinged. you can by pass the computer with jumper wires to the pump. if you have not checked the VST pump filter that will be one of the next steps. get the oring, buy a filter and just change it. yamaha reccommends clean/replace every 200 hours or once a year. <br />good luck and keep posting

 

[mcbc10195]

Re: 200 HP OX66 Surges above 1700 Rpm

Thanks for the replies. I did check the low pressure pumps and they are putting out a steady 4 psi. Is this to little. The voltage on the high pressure fuel pump is 13.55 to 13.65 volts. I did not know that it changes speed at 1800 rpm. I will take the VST apart tommorrow and see what I can find. Do the high pressure fuel pumps go bad often. It sounds like that is what it may be. Thanks again. Hope to hear more replies.

 

[BRIAN03]

Re: 200 HP OX66 Surges above 1700 Rpm

Most high pressure pumps fail from the fuel turning. If the engine has sat for any lenth of time. The fuel evaporates in the fuel chamber and the pump locks up from green fuel. Yamaha calles what they put the high pressure pump in the fuel chamber. The fuel chamber has a drain on it in the from of it. Pull that out and look at the flat side of it. If there has been bad fuel in the fuel chamber you will see it on the drain plug of the fuel chamber. If it looks like muds been in there or it has the smell of green fuel you need to clean the fuel chamber when you change the high pressure fuel pump. Dont forget the oring kit for the top of the fuel chamber.