Merc 5.0 fuel pressure issue

[Mark Lyon]

So I bought a boat first time out it dies on me. I wait 2 weeks to get it looked at at the marina. The mechanic has changed out the low pressure and the high pressure pumps as well as the fuel line itself. They say it runs on their tank hooked up directly to the pumps and cannot keep it running hooked up to the boat tank. What happens is that it starts and runs but sitting at a idle eventually the fuel pressure falls to zero and the motor then dies.

Please help I am missing yet another crab opening tomorrow and a trip to the San Juans. Just what do you do when the mechanic can't find the problem and fix it?

Frustrated beyond belief is this what boat ownership is all about?

Mark

 

[Ididntdoit]

anti siphon valve

 

[scoflaw]

Remove the tank pickup tube and check it out. Look at the tank vent make sure it's clear. Make sure the fuel solenoids aren't the issue

 

[Strecker25]

So I bought a boat first time out it dies on me. I wait 2 weeks to get it looked at at the marina. The mechanic has changed out the low pressure and the high pressure pumps as well as the fuel line itself. They say it runs on their tank hooked up directly to the pumps and cannot keep it running hooked up to the boat tank. What happens is that it starts and runs but sitting at a idle eventually the fuel pressure falls to zero and the motor then dies.

Please help I am missing yet another crab opening tomorrow and a trip to the San Juans. Just what do you do when the mechanic can't find the problem and fix it?

Frustrated beyond belief is this what boat ownership is all about?

Mark

as mentioned I would also pull the anti-siphon and take a look. Also remove the tank pickup and inspect it to make sure its not gunked up

if those are clear you might have a failed fuel line. You could test pressure while running as well. Is this a 5.0 TBI?

 

[Mark Lyon]

The engine is a 5.0 MPI. All has been check above except for the solenoids. What is a solenoid and what does it do?

 

[scoflaw]

Electrical device that replaced the anti syphon valve.to shut the fuel off. You talk about 2 fuel pumps so I assume you have the CF3

 

[Mark Lyon]

I do not know if it is a CF3. I do know the anti syphon valve is a brass coupler near the tank and was removed for a time to test if that was the problem.

 

[Mark Lyon]

I was reading a post in Iboat that talked about testing for an airbound/leaky system by placing a clear tube in the fuel line and looking for bubble. I assume air bubbles in the fuel like would lower the fuel pressure correct. I have been hanging around the boat yard quite a bit trying to leave and go crabbing as soon as the problem is resolved and I know he has not done this particular test. Your thoughts?

 

[scoflaw]

Wouldn't hurt. So what year is this motor? Could he be bullshitting you about running fine on another fuel source? Did he take it for a good shakedown ride?


Edit. Did he drain your tank completely? Maybe you got a pile of crap in there

 

[Mark Lyon]

So we did the clear tube test and air bubbles came from the pump back to the tank?? I would have expected the other way. No we have not drained the tank nor been away from the dock. I don't believe he is billshitting me here. Upon further discussion the pressure did drop also with their tank
pumps are back out of the noat and being bench tested now.

 

[Mark Lyon]

The boat is a 2011.

 

[scoflaw]

So it is a CF3 in 2011 and there is no return line from the pump to the tank. So this air you speak about ?

 

[Mark Lyon]

So the bench test: First they could not get the pumps to pump anything but a dribble. Then they took them out of the housing and dipped them in fuel and the pumped like mad. Put them back in the housing and noticed that the O-ring for the filter did not seal so thinking that was where we were getting the air he replaced the O-ring. Another pump test for about 4 minutes on the bench and it pumped fuel well. Placed the whole thing back in the boat and it fail again. It also failed again on their tank. Perhaps they did not run the bench test long enough as it takes about 10 minutes of idling for the the pressure to fall and the boat to die. The Merc rep is looking for a new complete element and will be down at the marina tomorrow morning. So far I have miss halibut, ling cod the Puget Sound crab opening and now the San Juan crab opening I am very disappointed to say the least.

 

[scoflaw]

It is a little tricky getting the pumps in, just right. With 2 new pumps you should be able to get it working. It's not sealing well and leaking on the inside.

 

[Mark Lyon]

So I wish to update the latest on this saga. The Merc rep came by the marina and the ran more test. They found that the water coolant side of the cool fuel 3 was clogged with salt crystals. Therefore it was surmised that the unit froze and cracked because all the water was not drained. A new complete unit is on order and will be here next week.