Vapor lock or something else?

[vetplus40]

Greetings. I experienced a condition with my 5.0 MPI that has me baffled. After being winterized with a full tank of fuel, I ran 30 minutes to the local sand bar. After about two hours, I tried to leave. The engine started, sputtered and died. I tried starting it for the next 30 minutes with no luck. All it would do was sputter and die. After a two hour tow back to the launch, the boat started right up.
I have owned this boat for 6 years. I have ran it harder on hotter days and done faster restarts and have never had an issue like this.
If I did have vapor lock, I would have thought that sitting for two hours would have sufficed for a "cool down" period. In addition, I did confirm via the Schrader valve that I had fuel at the fuel rails.
Could I have some other issue that has vapor lock symptoms but isn't vapor lock?
Thanks for any insight.

 

[alldodge]

It's very possible it is VL but first do you happen to have a serial number?

 

[Scott Danforth]

Can't have vapor lock with an EFI fuel system

So look at your fuel pressure

 

[Stinnett21]

I had a similar condition happen on my 5.0 MPI (serial #0M345638). There is a check valve in back of the fuel pump that I believe stops hot engine water from backing up into the fuel pump. The valve had come apart. This fixed mine. If you go to marineengine.com, put in my serial number, go to Closed cooling system (easy drain), it's part #2. Have no idea if your setup is the same.

 

[alldodge]

Can't have vapor lock with an EFI fuel system

Sure has happened to a lot of folks including me, please advise how it "can't" happen to MPI

 

[vetplus40]

It's very possible it is VL but first do you happen to have a serial number?

Let me try and find it.
I'm wondering if a full tank of winter blend gas may have caused it. Usually, I add fresh fuel after winter storage. Didn't do that this time. That said, having VL after six years strikes me as very odd.

 

[vetplus40]

It's very possible it is VL but first do you happen to have a serial number?

Serial number OM684952.

 

[vetplus40]

Serial number OM684952.

Fuel rail pressure about 42 psi.

 

[alldodge]

Fuel pressure is good and you have cool fuel and HVS ignition

To verify and temporary fix it, use saftey glasses, a baggie, a rag and small screw driver. The next time it does it, remove the cap off the schrader valve on the fuel rail. Put rag around schrader valve and press on tip a schrader valve.

Gas an air (vapor) should spew out and get caught by rag. Can cycle the key to get the vapor out. With it just gas, fire it up. If all is good put rag in baggie

The permanent fix is to reroute the cool fuel return line back to the tank instead of fuel filter

 

[Stinnett21]

Recommend starting by replacing the check valve mentioned in post 4. See what happens. It's an $80 part. Solved my vapor lock problems 700 hours ago.

 

[vetplus40]

Fuel pressure is good and you have cool fuel and HVS ignition

To verify and temporary fix it, use saftey glasses, a baggie, a rag and small screw driver. The next time it does it, remove the cap off the schrader valve on the fuel rail. Put rag around schrader valve and press on tip a schrader valve.

Gas an air (vapor) should spew out and get caught by rag. Can cycle the key to get the vapor out. With it just gas, fire it up. If all is good put rag in baggie

The permanent fix is to reroute the cool fuel return line back to the tank instead of fuel filter
View attachment 409743

Thanks for the info. Like previously stated, this was the first time that this has ever happened in 6 years of running this boat in very hot conditions. The only thing different this time was that the tank was completely full of winter gas and I did not mix in fresh fuel before going out. Because it had never done it before, vapor lock didn't even cross my mind. It actually sounded like water in the fuel. I have since checked the filter and it was fine.

 

[vetplus40]

Recommend starting by replacing the check valve mentioned in post 4. See what happens. It's an $80 part. Solved my vapor lock problems 700 hours ago.

Will do. Thanks.

 

[vetplus40]

I had a similar condition happen on my 5.0 MPI (serial #0M345638). There is a check valve in back of the fuel pump that I believe stops hot engine water from backing up into the fuel pump. The valve had come apart. This fixed mine. If you go to marineengine.com, put in my serial number, go to Closed cooling system (easy drain), it's part #2. Have no idea if your setup is the same.

Thanks for the info. Did yours restart after a cool down period with a busted valve?
Also, my cooling system is not a closed loop, so I may not have that valve. I will certainly check and see. Thanks.

 

[alldodge]

The amount of fuel or if it was from winterized fuel has no bearing on what happened. It all deals with fuel pressure and the amount of heat

 

[nola mike]

The amount of fuel or if it was from winterized fuel has no bearing on what happened. It all deals with fuel pressure and the amount of heat

Winter blended fuels vaporize easier

 

[jimmbo]

If it were going to Vapour Lock in a FI system, it would be between the Tank and the Lift Pump especially if there is a Filter in between, as that would be the only location that would have lower than Atmospheric Pressure. Downstream of that Pump the Fuel would be under Higher Pressure and far more Difficult to Flash.
I guess if there is a Filter, between the Lift Pump and the High Pressure FI Rail Pump, it could flash if that Filter was plugged, but only between the HP Pump and the Filter

 

[vetplus40]

The amount of fuel or if it was from winterized fuel has no bearing on what happened. It all deals with fuel pressure and the amount of heat

I appreciate the input. Im just evaluating what I did differently this year than previous years.

 

[vetplus40]

Winter blended fuels vaporize easier

I have read that on a chemical forum and I had a 100% full tank of it.

 

[vetplus40]

If it were going to Vapour Lock in a FI system, it would be between the Tank and the Lift Pump especially if there is a Filter in between, as that would be the only location that would have lower than Atmospheric Pressure. Downstream of that Pump the Fuel would be under Higher Pressure and far more Difficult to Flash.
I guess if there is a Filter, between the Lift Pump My and the High Pressure FI Rail Pump, it could flash if that Filter was plugged, but only between the HP Pump and the Filter

My fuel/moisture separator filter is new.

 

[Stinnett21]

Thanks for the info. Did yours restart after a cool down period with a busted valve?
Also, my cooling system is not a closed loop, so I may not have that valve. I will certainly check and see. Thanks.

Yes mine would restart after a period of time...say an hour or so depending on how hot the day was. I put your SN in and apparently you do have the same check valve.