2004 Yamaha F225 stalls at low rpm

[Dorado222]

2004 F225 Yamaha 450Hrs. The engine stalls at slow speed. Hope anyone can add to what I have done so far......

In the morning at first the engine starts and idles fine and going through numerous slow wake zones it does fine. We stopped at Peanut Iland for a couple hours and it stuttered and died in the slow wake zone. I pumped the fuel bulb and it started. About fifty yards further it died again and from thereon we had to keep pumping the ball to keep it running. At rpm it does fine lets say 4000rpm. Came to the ramp and did not want to start again after I backed my trailer in. Went home and opened the VST and checked that filter and it is clean.
We went scuba on Labor day and out to the dive site it ran fine but after the first shut down it did the same….stall at slow speed.

I checked the U shape filter on top….fine pumped gas through it.
I can hear the high pressure prime for a few sec after key is turned on.
Low pressure pump is off with key on, but primes with engine start so that is good, I had the fuel exit line off and it pumped good.
Low pressure pump cycles good 10 sec on 20 sec off when engine runs at idle.
I removed the pressure relief valve next to the low pressure fuel pump. I could not blow through it from either side. I connected my compressor at 20psi and it opened up and let the pressure drop ….at about 10 psi the valve closed. So that is good.

Next is I am going to connect two wires to the low pressure pumps terminals, take the boat out and if it happens again I will connect a voltmeter to those wires to see if I have current at the pump when it does that.

Do you have any other thoughts or ideas that I can check while I have it open. I am going to replace the High pressure fuel pump Viton grommet , part umber 68V-13781-00-00 because it has a small crack right at the top but I doubt if it is the problem because there is plenty of good grommet that would seal the transition from pump to the VST tank.

Thank you

[fairdeal]

if "pumping the ball" keeps the engine running fine,
then the problem has nothing to do with the high pressure pump,
nor anything else inside the VST -

the problem is the low pressure system failing to keep the VST full.

And that it runs fine at 4000 rpm
means something is handicapping the lift pumps's performance,
such that it can't keep up when it is only running part-time -
the 10 seconds on/20 seconds off below 1200 rpm -

the little pressure relief valve would be a suspect,
but you've checked that

clearly not a restriction, either on suction side or pressure side,
since the primer bulb is able to get the job done,
nor an air leak on the primer bulb's suction side

I would look for an air leak on the lift pump's suction side -
between it and the primer bulb;

- where the hoses attach to the little under-the-cowling filter housing
- the gasketing/sealing of that filter bowl to its housing


you only need one wire to make the lift pump run continuously:
find the black/white wire in the 6-wire plug
that goes to the pump driver on the port side;
backwire that terminal and connect it to ground -
the pump will run whenever the key is "on"










Video:

https://vimeo.com/manage/videos/271987959

[Dorado222]

Thank you, I will check for leaks for sure, My mind says to make sure there is no fuel in the under cowling bowl and fuel lines .. .pressurize the fuel lines and check with soap and water.

I will also ground the black wire when getting stuck again. This is great to eliminate the VST and just to concentrate from the tank to the lift pump. Thanks again Fairdeal.

[Dorado222]

Checked that everything was airtight between the tank and lift pump, then I removed the filter in the under cowl water separator bowl, I ordered a new filter but it did not come in yet, so I took a skewer and punched a hole in it Installed a new horseshoe filter on top and we were out all Sunday, Monday and packed up this morning at Peanut Island. No issues at all. When the under cowl filter arrives I will install it.
Thanks again.