4.3L EFI Fueling problems Mercruiser ((Help needed))

[lukecollins]

After 30 min approx running we stop the engine for 10 mins and it will not restart.

It would appear that the fuel pump is faulty, although it makes a noise we do not get any fuel back via the return line from the fuel pump to the filter and it pulls a small vac on the fuel filter return line socket.

What controls the fuel line pressure to the injectors on the EFI (2 injectors) and why dont we see fuel on the fuel return line back to the filter, this line remains empty when we can not start the engine.

The None return valve appears to be working fine although the suction pressure is fairly high needed when we suck the NRV. The fuel pick up is also fine and filter is clean on the tank and also the engine fuel filter. The problem starts when the water runs back from the engine to the fuel cooler. She will not run for approx 2 hours. After 2 hours she starts 1st time again.

 

[Don S]

Re: 4.3L EFI Fueling problems Mercruiser ((Help needed))

It's called an anti-siphon valve not a None return valve, and is only needed to prevent gas siphoning into the bilge should the line break. Has nothing to do with keeping fuel in the line. Matter of fact, the engine would run just as well with a plain hose barb fitting.
I would recommend you check your boats fuel system. A plugged vent line could cause the problem. as you use fuel, a vacuum builts till the pump can't pull fuel, and your engine dies. After a coupld of hours things equalize again.
Run the tests in this link and see if it's pulling a high vacuum when the engine dies.
http://forums.iboats.com/showthread.php?t=167561

 

[lukecollins]

Re: 4.3L EFI Fueling problems Mercruiser ((Help needed))

Thanks for the reply. I can not do the vac test as I do not have the meters etc.
I do however know that no fuel comes back down the recirculation line to the filter from the pump at any time is this correct and what controls the recirc line to the fuel filter.

Should the anti syphon valve be fairly strong say 1 psi to overcome the spring pressure in the elbow of the tank as its in the suction line of the fuel system. If I leave this out of circuit I get some bubbling in the bottom of my make shift fuel tank.

Thanks for your help.

Regards

Luke

 

[newport dave]

Re: 4.3L EFI Fueling problems Mercruiser ((Help needed))

There will be no fuel in the fuel return line unless you have full pressure to the regulator and then the regulator bleeds off the excess pressure to the return line. In other words You have low or no fuel pressure.

Quit messing around with "test" procedures that don't tell you anything. Purchase a fuel pressure and vacuum gauge and follow the instructions in the link that Don posted.

 

[lukecollins]

Re: 4.3L EFI Fueling problems Mercruiser ((Help needed))

THanks for the posts. We had another review today and noted that the water flows back to the fuel cooler when turned off and warms the fuel/filter when it restarts. Also we removed the syphon valve from the tank and we could not replicate the fault when the engine was warm. Would this indicate a faulty syphone (none return valve) or a weak pump. I assume the warming of the fuel is not an issue when the water runs back.

I can not run the test as we are 100 miles from the sea and want to try and sort the problem prior to visiting the sea again.

I can also hear the fuel pump over the engine below 1500 rpm ie it is fairly loud (not sure if its me picking up the sound or the pump is getting louder).

Thanks for the assistance guys.

 

[dcg9381]

Re: 4.3L EFI Fueling problems Mercruiser ((Help needed))

I had a similar problem on a Shortline Comp boat, with a Mag 350.
The motor would "heat soak" if shut down while hot, especially if tugging a load.
You could press the fuel relief valve, turn the key, all you'd get is fuel vapor.

For the Mercruiser, there was a service bulletin on fixing the issue, but it involved routing a lot of the fuel line away from the block. We simply learned to pop the engine cover if sitting after a hard run and/or running the fan.