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2008 Yamaha 250hp fuel problem

B

BubbaC

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The problem started only when I was at higher RPMs almost full throttle after running a few min at higher throttle I would lose power and motor would almost die. I would have to pump the prime ball to keep it running. Then if I stayed under 2000 RPM the boat would run great. I did some research and thought at first it was the anti siphon valve, I pulled it and the spring seemed fine and it was not stuck. I then did more research and learned it could be the fuel cooler or the low pressure fuel pump. I replaces every fuel line from tank to the fuel filter. I replaced the low pressure fuel pump the filter in line and the filter in the VST tank and new fuel filter housing and filter and new fuel water separator filter and hosing. Now my problem has gotten worse. After I pump prime ball and turn ken on for 10 sec to prime motor starts and runs great. It will run at idle for 5 to 10 min then die. If I am running in the water at 1500 rpm it will run for 1-2 min then just die. If I get up to full throttle. it only gets about 30 sec. before dying. If I hand pump the prime ball it will continue to run fine. The motor dose not run ruff or anything just runs out of fuel and dies. The initial problem that I thought was low fuel pump, well it was the low fuel pump fuse blown. But not I have taken this all apart to fix I have caused another problem. Can anyone help?

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If pumping the primer bulb keeps the motor running continuously, but when not pumping the primer bulb the motor will stop running, that is telling me that the low pressure lift pump (feeds the HP pump in the VST) is not doing its job.

The LP pump runs intermittently when below 1200 RPM and continuously when above 1200 RPM.

The ECU applies a ground to the LP pump to cause it to run. Battery power is applied continuously to the LP pump when the key is on.

Have you tested the electrical inputs to the LP pump?
 
boscoe said:
If pumping the primer bulb keeps the motor running continuously, but when not pumping the primer bulb the motor will stop running, that is telling me that the low pressure lift pump (feeds the HP pump in the VST) is not doing its job.

The LP pump runs intermittently when below 1200 RPM and continuously when above 1200 RPM.

The ECU applies a ground to the LP pump to cause it to run. Battery power is applied continuously to the LP pump when the key is on.

Have you tested the electrical inputs to the LP pump?
Click to expand...
Thank you for your replay and help

What is strange is before I started messing with it, the boat ran great, just not at high throttle.
I did not start checking the electrical until after it wouldn't stay running during my first try after installing the new LP, filter ,filter housing, new fuel water sep housing and all new lines from tank.
I hen found that the fuse to the LP (5a) had blown. (don't know if this is what was causing the problem from the very begging) But new fuse has not improved status.

for trouble shooting purpose--
I should have 12v at the red wire on the LP at all times when the key is on?
on ground wire I should have continuity to ground/ or 0 volt on black wire? How often after key in on if motor is not running should the ground continuity happen?
I hear another buzzing sound in the motor that is not coming from the VST, could that be the ECU?
Could the HP in the VST be too week?
 
The buzzing is the electronic throttle valve.

Yes to battery voltage at the LP pump when the key is on. A voltage drop at the LP pump could cause the pump to run abnormally slow which might cause the fuel pressure to be too low. Starving the HP pump at times. Or the pump could be deficient.

No ground continuity on the black wire unless and until the ECU applies the ground. Ground is applied for several seconds when the key is first turned to the on position. Ground is applied while the engine is being cranked. Ground is applied for 10 seconds out of every 30 seconds when the motor is running below ~1200 RPM. Ground is applied continuously when the motor is running above ~1200 RPM.

You might want to plumb a fuel pressure gauge to the VST HP pump output so as to better see what is going on and when.
 
boscoe said:
The buzzing is the electronic throttle valve.

Yes to battery voltage at the LP pump when the key is on. A voltage drop at the LP pump could cause the pump to run abnormally slow which might cause the fuel pressure to be too low. Starving the HP pump at times. Or the pump could be deficient.

No ground continuity on the black wire unless and until the ECU applies the ground. Ground is applied for several seconds when the key is first turned to the on position. Ground is applied while the engine is being cranked. Ground is applied for 10 seconds out of every 30 seconds when the motor is running below ~1200 RPM. Ground is applied continuously when the motor is running above ~1200 RPM.

You might want to plumb a fuel pressure gauge to the VST HP pump output so as to better see what is going on and when.
Click to expand...
Again, I cant thank you enough for your feedback and help.
What I found:
Because you talked about voltage I decided to start at the fuse. The 5a fuse was blown. I replaced.
I started by checking continuity between the 0v (ground terminal/black wire) to ground without key on first. No continuity
I then checked continuity between the 0v and ground while someone turned on the key. No continuity
I then put meter on DC and checked the +terminal to ground. with key off not voltage
then with key on I got 12 volts
I then checked by placing my red on red and black on black terminals on LP and got no voltage with key on
I then went around and found the ground wires coming out of the relay box and others (two dif bolts) just looking at them they did not look bad. But I loosened them worked the wires back and forth to give them some scratched surfaces.
I then did the continuity check again between the black terminal on the LP to ground with key off, not continuity
With key on I had continuity
The continuity would last precisely 13 sec after key was turned off.
The really strange thing is I get continuity to ground on the black terminal, I get 12v at the red terminal when I check it to a ground, but I do not get 12 v between the two terminals and the pump and it is not pumping fuel out of the hose when the key is in the on position.

Standing back scratching my head!
 
I did a little test to see if the pump is working. I put a jumper from the black terminal to ground. (I ran outlet line to a bottle) Had the key turned to the on position, Got plenty of fuel, for 13 sec after the key was turned off.
So I have continuity to ground when key is on, but not a true 0v when key is on.
 
I am not sure we are on the same page.

With the key on the pump has battery power to the positive terminal of the pump. At key on the ECU grounds the black wire. The pump runs. Or it should. The engine starts and runs. The black wire remains grounded by the ECU (intermittently below 1200 RPM and continuously above 1200 RPM.

If the key is on (battery power to the pump) but the motor not running (say the starter switch was not turned to the cranking position) the ECU disconnects the ground after a period of time. Battery voltage remains to the positive terminal of the pump motor. Voltage will be seen on the black wire but it will be less than battery voltage. Because of voltage drop across the pump motor electrical windings.
 
We are on same page, I was just running several different test and getting different readings, with key on and key off. I really thought that because the key on gave the positive terminal 12 volts and the ECU gave the black terminal continuity to ground. I thought the pump would just energize and pump fuel out of the outlet.

The ECU is putting .08 dc volts to the 0v terminal (without a load) when the key is on. This last 13sec after key is turned off.

I am starting to think I had a bad ground, hits the first time I checked the ECU ground to black terminal I did not get continuity. After messing with ground terminals and getting better connection I started getting the continuity to ground with key on.

I wonder if the bad ground was what caused the fuse to blow as it was working hard and heating up the circuit. It is only a 5a fuse.

I will put the manifolds back on tomorrow hook it to water and test it.
 
with no load, using the (+)positive probe on meter on the blue wire coming from ECU and the ground probe on motor ground I got .08v dc when the key was turned on. I got 12.5v dc when on the positive side of the pump feed from fuse with key on.
 
boscoe said:
I am not sure we are on the same page.

With the key on the pump has battery power to the positive terminal of the pump. At key on the ECU grounds the black wire. The pump runs. Or it should. The engine starts and runs. The black wire remains grounded by the ECU (intermittently below 1200 RPM and continuously above 1200 RPM.

If the key is on (battery power to the pump) but the motor not running (say the starter switch was not turned to the cranking position) the ECU disconnects the ground after a period of time. Battery voltage remains to the positive terminal of the pump motor. Voltage will be seen on the black wire but it will be less than battery voltage. Because of voltage drop across the pump motor electrical windings.
Click to expand...
Your input was very helpful. So thank you very much. I was looking for a fuel line air leak the whole time. I am not 100% certain my issue is fix but I was able to run the motor (without blowing the fuse) several time holding different RPMS for more than 1.5 min periods. It ran and sounded great with never any fowl or flutter. I will try to get it in water as soon as I can to run it
Thanks again I will update
 
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