Solution 225 OX66 stalling

[Florida Tim]

In the florida keys today and my buddy's 1999ish 225 ox66 fuel injected Yamaha would not start. It is labor day weekend and help was hard to come by. My friend had been having this intermittent but recurring problem with the motor cutting off. He recently had the VST tank clean and serviced. I maybe know enough to be dangerous with the motor but gave it a shot. Figured out that the high pressure fuel pump was not coming on. Pump works as we were able to disconnect and put 12 volts to it and got it to spin. Finally got a mobile mechanic to stop by. With various checking it was determined that the problem was the fuel pump start relay. This relay also gives positive voltage to the injectors. So when it goes there is no fuel to the cylinders. Found a couple of used ones on a Saturday afternoon on labor day weekend in the Florida keys but they did not work. They would work for a bit and stop or work sometimes. Another mechanic actually built a new one by hooking up a seimens relay to the wires from one of the non working relays. About the same size and fits in the space. Not sealed like the original but it is now working consistently and motor runs. Actually seems like the fuel pump is running a little stronger. So here is my theory...I believe that the original Yamaha fuel pump relay becomes weak and becomes a resister dropping voltage to the fuel pump which turn draws more amps until it over heats and quits and the motor stalls like you pulled the dead man switch. So the moral is to also consider changing the fuel pump start relay if you are having stalling problems.

 

[99yam40]

Re: Solution 225 OX66 stalling

You need to check to make sure pump is not pulling too many amps after running for awhile as that will cause problems,
relay is not normally the cause for pump motor to pull higher amps

 

[Florida Tim]

Re: Solution 225 OX66 stalling

Thanks for the reply. Did think of this. Spoke to the mechanic by phone that serviced the vst/pump. Said he bench tested the pump and it started easily. Second mechanic said that when the high pressure pump begins to go bad they make more noise. My theory is based on the fact that we had three different relays in our hands on the day in question and all three malfunctioned to some extent. All were used OEM parts that were 10-12 years old. Given the vintage of these motors and how many hours they may have, these relays may just be getting old.

 

[Florida Tim]

Re: Solution 225 OX66 stalling

My theory about higher amps is that too much resistance across the relay will lower the voltage. To do the same amount of work at a lower voltage pump will either draw more amps. Or pump will just run a little slower.

 

[99yam40]

Re: Solution 225 OX66 stalling

DC motors will just slow down , that is why Yamaha uses a resister on some at slower Rpm as not as much fuel is needed.

Ac motors try to keep the same RPM and draw more amps to get there if voltage drops

just an opinion from an electrician of 30 years

 

[Florida Tim]

Re: Solution 225 OX66 stalling

Thanks for the feedback. I still believe that these relays are overheating after a bit of running and failing. Lower speed of the fuel pump would lower the fuel pressure to the injector rail. The intermittent behavior of this mode a failure I think can frustrate greatly. Anyway the rigged up seimens relay saved our trip to the keys.

 

[99yam40]

Re: Solution 225 OX66 stalling

I would be a good idea to monitor rail pressure and the amps the pump is pulling to be sure all stay in spec
Relays and the ECU are only good for normal amp draw, over current will make them fail