Mercruiser 4.3 EFI 6 Cyl

[CHI]

A friend of mine has a Searay boat with a Mercruiser 4.3 EFI 6 Cyl petrol engine.
The boat starts from cold with no problem at all. The boat will run perfectly for many hours, but once the engine is switched off it will not re start. On occassions the engine will fire up , but run very roughly, backfire and die. Other times it will not start.
Once the engine has cooled down it will re-start okay and run well.
There is fuel on the plugs and also a spark from the plugs/HT leads.

Any Ideas what could be the cause!!

Many thanks

Keith

 

[tinkicker0]

Need to test the HT coil for starters. I think it may be breaking down as it gets warmed up.

 

[Alrob]

my last boat which had a 350 magnum came with a cool fuel module and I believe it was to stop vapour lock when engine was warm although I could be talking ****e

 

[Kendal]

Vapor lock is a possibility but I would also not rule out an electrical problem even if you have a spark. I think the engine has an electric fuel pump and obviously an ecm. A bad connection may be cutting the supply somewhere which may not affect the engine while running due to the vibration. It would be worth having a good look for bad connections or even chafing on the wires which run across the engine, which may have broken down the insulation.
Good luck.
Dave

 

[davedpc]

Have you checked inside the dist. cap for cracks or tracking?

 

[spannerman]

When it happens next, turn the ignition on and listen for the electric fuel pump to run for a couple of seconds as it primes the system, if thats OK, then take out the centre lead on the distributor cap and place it near an earth and crank to see if you have a good bluish spark. If not then you need to check the coil with an ohm meter, if thats OK then its probably the Hall effect sensor in the distributor, I have never changed an ignition module on a Mecruiser yet, have changed several Hall sensors.
If you have a spark, them you need to check the fuel pressure to see if its holding 'rest pressure' after switch off.

 

[gingie]

merc 4.3

Fuel on the plugs so the pump is working.

A faulty pressure regulator can also cause bad starting. The fuel pressure rating on load is 35 psi. Can creep up to 43 psi. If the regulator is allowing more then the injectors just hose in the fuel and theoretically flooding it.

As this sits pretty much in the bilge along with the pump they are prone to corroding and failing

 

[CHI]

Many thanks for all the answers. I will pass the info on

Keith