2 year old Mercury 4 stroke running strange?

[wijames]

I have a 2 year old Mercury 40 EFI Bigfoot that has started having a strange problem. It starts fine and idles good for a couple of minutes then starts running rough. If youleave it running it will smooth out within a couple of minutes and then again run rough after a few. Also if I throttle up to 1500-1800 RPM it will run fine for a couple of minutes and then quit. I can start it right back up and it will do the same thing. It seems to run fine at FOT but even then it won't reach maximum RPM. I've emptied the fuel tank and ran a complete fresh tank of fuel through it to see if it was bad gas. I also changed the primer bulb and fuel/water filter. The engine just had it's 100 hour maintenance two months ago and the problems started shortly after that but the Mercury dealer insists that it couldn't be anything they did during maintenance. Any ideas or suggestions?

 

[wijames]

Re: 2 year old Mercury 4 stroke running strange?

Come on guys, somebody must have some suggestions?

 

[MH Hawker]

Re: 2 year old Mercury 4 stroke running strange?

It is a fuel problem, but NO idea what it would be, I would run some sea foam through it and check the tank venting and fittings, it may be sucking air some place.

 

[Scott Danforth]

Re: 2 year old Mercury 4 stroke running strange?

I agree it sounds like crud in the fuel system.

if it was carbed, I would say pull the bowls and look.

However I have not worked on an EFI OB yet. Is there a filter after the quick-connect fitting?

 

[wijames]

Re: 2 year old Mercury 4 stroke running strange?

I agree it sounds like crud in the fuel system.

if it was carbed, I would say pull the bowls and look.

However I have not worked on an EFI OB yet. Is there a filter after the quick-connect fitting?

Yes but they replaced it during the 100 hour service.

 

[MH Hawker]

Re: 2 year old Mercury 4 stroke running strange?

Give it a twist and see if its lose. But same thing I haven't had to work on a EFI.

 

[Scott Danforth]

Re: 2 year old Mercury 4 stroke running strange?

Yes but they replaced it during the 100 hour service.

so replace it again. maybe a bunch of dirt made it past the filter and your injectors are now clogged. maybe the clamps are not tight and you are sucking air and leaning out the cylinders.

 

[Silvertip]

Re: 2 year old Mercury 4 stroke running strange?

Come on guys, somebody must have some suggestions?

You said: The Mercury dealer insists that it couldn't be anything they did during maintenance! Of course they would say that. But isn't it ironic that the problem popped up immediately after they worked on it. So don't make us drag information from you. You told us how the engine behaves but you have not told us what exactly they did at this 100 hour service?

Did you refill the fuel/water separator before installing it? Are you certain there is currently fuel IN the filter? Are you squeezing the primer bulb when the engine begins to die? This would help in determining if fuel is actually getting to the engine. Could be a high pressure pump going bad. Try a different fuel tank.

 

[wijames]

Re: 2 year old Mercury 4 stroke running strange?

You said: The Mercury dealer insists that it couldn't be anything they did during maintenance! Of course they would say that. But isn't it ironic that the problem popped up immediately after they worked on it. So don't make us drag information from you. You told us how the engine behaves but you have not told us what exactly they did at this 100 hour service?

Did you refill the fuel/water separator before installing it? Are you certain there is currently fuel IN the filter? Are you squeezing the primer bulb when the engine begins to die? This would help in determining if fuel is actually getting to the engine. Could be a high pressure pump going bad. Try a different fuel tank.

They changed all of the fluids, checked and greased the fittings and the prop shaft and replaced the fuel filter and fuel/water seperator. Since then I changed the fuel/water seperator again and yes I filled it before install. I can pump the ball and the filter fills up and when I start the engine the fuel slowly goes down in the filter but not all the way empty. I tried pumping the ball while it's idling poorly and the filter fills up but doesn't change the way the engine is running. I plan on trying a portable tank this weekend with some injector cleaner in it as well as check to see if the fuel tank vent is clogged and check the hose fittings. I'm also going to pull the plugs to see how they look. Is there anything else you can think of that I should check?

 

[Scott Danforth]

Re: 2 year old Mercury 4 stroke running strange?

you have an air leak in your plumbing somewhere if the fuel level in your filter is going down and you are not drawing fuel

 

[Lino]

Re: 2 year old Mercury 4 stroke running strange?

Not sure what you have for a fuel filter, any chance the old gasket was left behind with new one also.
Definitely sounds like fuel related problem.

 

[wijames]

Re: 2 year old Mercury 4 stroke running strange?

Not sure what you have for a fuel filter, any chance the old gasket was left behind with new one also.
Definitely sounds like fuel related problem.

This weekend I checked the fuel filter and the gasket was OK. I also changed the fuel tank vent and put in fresh fuel with some injector cleaner in a removable tank. I ran the engine at differing speeds for almost an hour and at idle the engine still acts like it has Parkinson’s disease and at FOT I can get no more than 5000 RPM. I also noticed that the last ? of the throttle does nothing. Really strange.