Hi guys,

I have been working with my new-to-me 415 HP Mercruiser 502 Mag MPI for a couple of weeks now. It is rebuilt just 10 hours ago, so the engine runs great, 30 PSI oil pressure when hot idle, purring at 600 rpm.

I did not do the actual rebuild myself, but I did the installation work in my boat. I have had some issues during the break-in period, had to replace the manifolds, and broke one impeller. Just for peace of mind I did the ICV and TPS at the same time. The engine had not run for 4 years prior to my purchase.

My current issue came now when I had run my first 10 hours. I have eagerly waited for 10 hours to do the first WOT run, and today was the day! In a nice breeze and 2 fot chop I went for my first WOT run (over 4000 rpm) and..... the engine dies! When I hammer the throttle at 4000 rpm it just dies! And the engine doesnt recover until I pull the throttle back again. Then it runs perfect again.

So basically it runs perfect under 4000 rpm and like crap over 4000 rpm.

So my first thought is fuel. Can it starve? My fuel filter looks new, but on the other hand I have no idea what has passed through it during the last 10 hours.

What else? Can Limp Mode give these symptoms?

Any thought would be very appreciated, the season over here in Sweden is too short to have the boat in the shop.....


Regards,

Johan

I'll go first....

What about VST screen? Do I have one in my MPI? I would guess it is a 1997 model year.


Regards,

Johan

I have a 1997 with cool fuel, just to narrow the issues down....


Regards,

Johan

Anti-siphon valve/s??

Hi, I just replaced the fuel filter, which was full of old crap even though it only had 10 hours. 5200 rpm's, the boat move like a fighter jet now.... :-)

So lesson learned, a 502 run better with fuel than without!


Thanks,

Johan

Thanks for posting up the Final Answer! Between the ethanol mix crap picking up water, and low octane questionable gas storage at some places, fuel filter changes probably a good idea...