mercury magnum 350 mpi engine cut out problems

[blackcat2008]

I am currently going through the process of running in a Mercury Magnum 350 mpi engine. My initial 2 or 3 trips were successful, however i have now uncovered a problem that is causing a headache.

The engine has recently developed an intermittent complete cut out and immediate switch off (no burbling or stuttering was heard). This has become more frequent during the most recent 2 trips. I have replaced the fuel pump relay as intitally i thought the problem was with this relay not continuing the fuel flow when taking over from the start up relay after 20 secs of running. The problem seems to be more frequent between 2500 and 4000 rpm, however it happens in differing rev ranges including tick over of around 1500 rpm.

The engine has only 3 hours on it, and i am yet to push the revs past 4000 rpm. One of my own thoughts are that it could be a built in 'safe running in cut out', however i would be surprised by this as it could cause a serious safety problem.

If anyone has an idea then it would be much appreciatred and save some head scratching.

 

[Don S]

Re: mercury magnum 350 mpi engine cut out problems

If you are going to ask EFI questions in this forum, you better have the Mercruiser SN for your engine. Even a year would narrow it down a little, but we have nothing to go on here. No year, no SN, nothing. All Mag 350 MPI engines are NOT the same.

 

[blackcat2008]

Re: mercury magnum 350 mpi engine cut out problems

Hi Don,

Sorry i didn't realise there is such a variation in engines! The engine was bought in 2008 however it may be a 2007 model (can't find paperwork to confrim which year). However the model number is 4-442067U U and the SN number is 1A301229.

Any advise would be useful.

F. Ruit

 

[newport dave]

Re: mercury magnum 350 mpi engine cut out problems

It sounds like the ECM is losing power, with a few possible causes being the ignition switch, lanyard switch and ten pin (or 14 pin) connections. If you can determine that everything is ok (no loss of power at any time) up to the engine, I would then turn it over to the warranty guys.