Low Pressure Fuel Problems - Only in water

[christianL]

When I connect the flushing adapter (rabbit ears) to my 07' Yamaha F225TXR it will run all day long, either in idle or with advanced throttle. But when it is in the water, it will not run at all. The guy at the shop says it's the low pressure fuel pump not working. That's fine, but what is the difference between the motor being in the water versus being hooked up to a water hose?? In other words, what changes in the fuel system when the motor is in the water? This is one of the weirdest things I've seen in a while. Any thoughts, suggestions, or ramblings on the issue? Any help would be great. Thanks!

 

[reeldutch]

Re: Low Pressure Fuel Problems - Only in water

if its the low pressure fuel pump than when you squeeze the primer bulb you fill the vst again and is should run. until the hp pump uses up the gas in the vst.

the only thing different in the water or out of the water is back pressure.
there is absolutely no load on the motor on muffs.
the low pressure fuel pump might have not have a problem on the muffs because there is the least amount of demand on the pump.
put a slight load on it(back pressure) and it might not keep up with the demand of the hp fuel pump.
could be.
only a 10 psi fuel pressure gauge and a vacuum gauge will tell you precisely whats going on with the pump.
tell us more about the motor somethings missing.


good luck

 

[christianL]

Re: Low Pressure Fuel Problems - Only in water

I should not have left that out. Yes, I can keep it running by squeezing the primer bulb when in the water, squeezing the bulb is not necessary with the muffs. When I stop squeezing the bulb, it dies after a few seconds. Would the exhaust backpressure from the motor being in the water cause enough load for it to not even idle?? Keep in mind that with the muffs, not only will it idle just fine, but I've had it at 1500 RPM for a few minutes (cannot go for too long b/c of possible overheat) and it runs fine - no bulb squeezing. Thanks

 

[rodbolt]

Re: Low Pressure Fuel Problems - Only in water

check that at idle,below 1200 RPM the low pressure pump cyles on 10 seconds and off 20 seconds. above about 1200 rpm the LP runs continuously.

 

[christianL]

Re: Low Pressure Fuel Problems - Only in water

That is correct, I checked that last weekend and I could hear the pump running on for 20 off for 10 as well as watch the fuel level drop in the filter bowl as the LP pump ran. It also runs continuously above 1200. Maybe it could just be weak? I know the pump is electric, but i'm sure as to the internal construction. I believe it is too early to rule out a computer malfunction at this point. does anyone agree? could there be a vacuum sensor or pressure sensor bad giving a false indication to the ECU?

 

[rodbolt]

Re: Low Pressure Fuel Problems - Only in water

no sensors or anything like that and its not an ECU issue, could be the check valve for the low pressure recirculation line.