Mercruiser problem..fuel maybe? Help!

Mikebailey · 11 October 2005, 23:17

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 · 12 October 2005, 01:54

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 · 12 October 2005, 02:35

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 · 12 October 2005, 09:39

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 · 12 October 2005, 12:36

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 · 12 October 2005, 14:09

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 · 12 October 2005, 14:11

Quote:

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 · 12 October 2005, 16:59

Quote:

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 · 12 October 2005, 17:18

Quote:

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 · 12 October 2005, 17:55

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....

Mikebailey · 12 October 2005, 18:16

Quote:

Originally Posted by codprawn

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!!!

That sounds plausible as if I put the hammer down hard it coughs and splutters, I can get it up to 3500RPM but only if I go easy. If i try to welly it too early I get the splutters again.

Mollers · 12 October 2005, 18:18

Hi Chris. Yeah, pretty much. As long as he takes it to a Merc agent they'll plug it in and it should diagnose the prob pretty quickly. The 5ltr EFI is quite new, less than 5 years. It kicks out about 260HP which is the same as my old 5.7 carb model which had a four barrel Holly. At full chat it was like pouring fuel out of a bucket. The EFI is more economical and more reliable. Shit in the carb was a constant problem. Getting one's arse over the air filter was awkward!!

Mollers · 12 October 2005, 18:23

Mike, If you are in the South there's a guy called Andy Judge of Marine Propulsion based in Southampton area. I used him for a mechanical survey once. He's pretty clued up and not crazy when writing out a bill. Talk the hind legs off a donkey though!

Hugh Jardon · 12 October 2005, 18:25

Quote:

Originally Posted by Mollulnan

Getting one's arse over the air filter was awkward!!

mollers, did it not have a porcelain dining table for curling one down in then?

Mike....seems best to get a merc guy to plug his box of wonders in and see what that comes back with

Mollers · 12 October 2005, 18:27

The Ribtec patent "Shit in the carb" apparatus! It saves shoving ya' bum in the engine bay!!

Hugh Jardon · 12 October 2005, 18:31

Quote:

Originally Posted by Mollulnan

The Ribtec patent "Shit in the carb" apparatus! It saves shoving ya' bum in the engine bay!!

is that why your mrs said you have V8 branded on your bum from when you slipped one day?

Mollers · 12 October 2005, 18:38

Quote:

Originally Posted by Hugh Jardon

is that why your mrs said you have V8 branded on your bum from when you slipped one day?

And "Goodyear" on me nuts from the power steering belt!!!

timboli · 12 October 2005, 20:39

Mate of mine with a 5 litre carb engine says Dave at http://www.southwater.com/
was very helpful when he had a problem

Mollers · 12 October 2005, 20:54

Quote:

Originally Posted by timboli

Mate of mine with a 5 litre carb engine says Dave at http://www.southwater.com/
was very helpful when he had a problem

The 5ltr carb model was a rare bird in this country. It must have been quite old. The more common in the UK were the 4.3ltr V6 Ford lump or the 5.7ltr V8 GM chevy lump which also appeared in virtually every muscle car ever built in the states. Incidently, the same GM lump is used by Mercruiser, Volvo and Yamaha. It's only the colour that varies.

Jizm · 12 October 2005, 22:01

If it is injected then it's worth checking for air leaks.