Mercruiser problem..fuel maybe? Help!

[Mikebailey]

I wonder if anyone can help. I have a mercruiser 5L petrol engine. Last weekend i fuelled it and took her out. She ran ok up to 3500rpm, about 22 knots. Applying any more throttle however resulted in the engine missing and spluttering and never achieving any more than 3500rpm.

I have tried to contact a local marine engineer who has not returned my calls. I am hoping its something simple that I can do myself but at the moment don't know where to start. Any help would be most welcome.

[Jizm]

firsty of all, welcome to ribnet. It does sound fuel related, how long since you used the boat?

another forum to try for engine probs is the yank one iboats

[codprawn]

I would also say fuel - either a blocked breather or blocked fuel filters - try taking off the fuel cap - see if that helps. Also check for blocked jets in carbs.

If it isn't that could be electrical - coil breaking down on load or similar.

[Mikebailey]

Thanks Jizm, I used it last at the weekend just gone and have not tried it since. I am worried that I am going to inflict damage if I use it before I understand what the problem is.

[Swifty]

Not knowing this engine, is it injected or carb?

Cos it sounds like fuel starvation, could possibly be the second stage jet blocked up?

Dunno. Might ring some bells for someone.

[Mollers]

I'm pretty sure that the 5ltr mercs are all EFI. In which case it wont be a blocked jet.If it's running fine up to 3500rpm then I'd suggest an engine management fault. It may be sensing a problem and limiting the revs. Best bet is to get it hooked up to a Merc comp whichwill detect the problem. I'd be surprised if it is fuel. If the filters were blocked, she'd struggle to run at all as the pump wouldn't be getting enough fuel to generate pressure.

[Mollers]

Originally Posted by Mikebailey

I wonder if anyone can help. I have a mercruiser 5L petrol engine. Last weekend i fuelled it and took her out. She ran ok up to 3500rpm, about 22 knots. Applying any more throttle however resulted in the engine missing and spluttering and never achieving any more than 3500rpm.

I have tried to contact a local marine engineer who has not returned my calls. I am hoping its something simple that I can do myself but at the moment don't know where to start. Any help would be most welcome.

Where are you based Mike?

[codprawn]

Originally Posted by Mollulnan

I'm pretty sure that the 5ltr mercs are all EFI. In which case it wont be a blocked jet.If it's running fine up to 3500rpm then I'd suggest an engine management fault. It may be sensing a problem and limiting the revs. Best bet is to get it hooked up to a Merc comp whichwill detect the problem. I'd be surprised if it is fuel. If the filters were blocked, she'd struggle to run at all as the pump wouldn't be getting enough fuel to generate pressure.

I was thinking of older carb engines - bloody efis get everywhere!!!

As to the fuel problem yes it IS still possible - I had a case where an engine would get enough fuel to run up to a certain power but then the pump couldn't deliver anymore due to a blockage. Come off the power again and it was fine!!!

[Hugh Jardon]

Originally Posted by codprawn

I was thinking of older carb engines - bloody efis get everywhere!!!

cough!.....bullshit......cough! i think you got caught out on that one codders, me old fruit...

[Hugh Jardon]

hey mollers,


do the 5l mercs have the same sort of diagnostics capabilities as the optis have in that they record all the faults and when they occurred etc, if so then all this guy needs to do is get it connected up, as you suggested, and it should pinpoint the problem relatively easily i would guess or hope....