Mercruiser failure to start

[Cal>air]

2003 mercruiser 350 mag mpi, started up great today ran it across the lake 5 min ride. Shut it off to check out the water, when I tried to start it no go. It would sputter a little, and cough a little smoke out of where the air filter is. Any ideas what is going on? 167 hours, regular oil changes, ran fine last week, lake elevation is at 10,000 feet water temp 40°f, normally run a lower elevations never run at this lake before.

 

[Bondo]

Ayuh,.... Welcome Aboard,.... Donno why ya posted this in the OMC forum,.....

How 'bout I move this to the Mercruiser forum for ya,.....

 

[sogood]

Is it possible you got water in your fuel? It might have run good initially by burning off the fuel in the carb, filter, separator before drawing contaminated fuel from the tank. Do you have a water separator fitted? If so I'd check it out.

 

[alldodge]

I'm thinking vapor lock
Does it start fine now, or will it still not start?

 

[Cal>air]

I brought it home and it started perfectly. I have a fuel/water separator installed, I think the fuel is good will check it. Can vapor lock happen in in this engine it's efi I thought..

 

[alldodge]

Can vapor lock happen in in this engine it's efi I thought..

Yes, it doesn't happen with a crab, only EFI or MPI

 

[Cal>air]

So to see if it is vapor lock should I just open the fuel cap when it dies and it should start up correct? Thanks.

 

[Bt Doctur]

Yes, it doesn't happen with a crab, ? thought they had gas too

 

[alldodge]

So to see if it is vapor lock should I just open the fuel cap when it dies and it should start up correct? Thanks.

No, Vapor Lock (VL) has nothing to do with the tank, it forms gas vapor in the fuel lines between the high pressure fuel pump and the injectors. If its VL, need to find the shrader valve and have a rag. Take the cap off the shrader valve, put the rag it front of it, then push in on the valve. If some vapor comes out, that's what it is.

Pushing in on the valve will also release the vapor and you should be able to start the motor. Also after it cools down it will fire right up. There are fixes but many just run their blowers longer and open the engine hatch to let heat escape

 

[Cal>air]

I will do some testing to see if we have a vapor lock issue or any fuel related problems. Will good fuel line insulation stop a vapor lock from occurring?

 

[alldodge]

I will do some testing to see if we have a vapor lock issue or any fuel related problems. Will good fuel line insulation stop a vapor lock from occurring?

No

The issue is heat soak develops in the fuel rail and most often happens mainly with MPI models. The fix is to change the return fuel back to the tank instead of to the fuel filter. By returning to the tank, there is cooler fuel always available and heat soak is not such a problem'

 

[Cal>air]

How do I tap back in to my fuel tank for return? Ran it on a fake lake for a while tonight, got it up to the same temp as it was on the lake 160°f let it run at that temp for similar time it took to cross the lake. I shut off the motor for a bit to simulate what I did when issue occured and it started perfectly fine this time. Tested for codes via obd2 no errors. Also checked fuel lines for vapor at rails did not find any vapor when pressure release was pushed. Going try to modify fuel return as AllDodge diagram shows.

 

[alldodge]

The motor produces more heat running on plane then on a hose. Don't think it would ever happen on a hose.

So far as back to the tank, many run it back to a Tee fitting installed in the fuel fill line if you don't have an unused fitting.

VL can also happen do to other things like a fuel restriction, it just shows up when its hot. The Merc fix was to install a boost pump which did help but not a total fix with some boats. Other manufactures like Indmar route the return back to the tank

https://www.perfprotech.com/blog/articles/mercruiser-vapor-lock