Merc 40 4s EFI stalls on full-throttle

Post by **curls** » Mon May 05, 2008 12:34 pm

Hey guys,

I borrowed my uncles' boat this past weekend for the BoQ walleye opener. It's a 15' Legend with a 40hp Merc 4-stroke EFI on the back. I'm not too familiar with outboard engines but overall have decent mechanical knowledge.

The engine idles 100% fine and cruises and planes out fine, but the problem is that most times while at full-throttle or very close to it, the engine will be fine for a while and then just sputter and die, exactly like when you run an outboard out of gas. The fix is to pump the fuel ball a few times again, and then voila, it's fixed for anywhere from 2-10 minutes of time again (and rinse, and repeat).

I am sure this has to be a fuel delivery issue. Could it be a clogged fuel filter (is there a fuel filter in the engine?)? Or is it a bad gas line that is losing its prime? I have never once smelled gas or oil with this engine, nor has he.

What else can him or I check? If all else fails, he'll bring it back to Hurst Marina where he got it and will get them to look at it, but obviously DIY on the easy stuff is always cheaper and more rewarding. I've also heard of http://fish-hawk.net/index.php?page=81 <-- this guy. Since the boat is located on Big Rideau just outside of Perth, Franktown might be a bit more accessible and quicker to get to.

Any opinions on what to check/replace?

Thanks,
Eric

Post by **troutnmuskiehunter** » Mon May 05, 2008 1:19 pm

This happened to me last year with my 40HP and it ended up being a bad fuel line connector on the tank....

Post by JP » Mon May 05, 2008 1:56 pm

Change the fuel prime bulb and you should be ok.

JP

Post by **Badger Shark** » Mon May 05, 2008 3:58 pm

I had the same problem with the same boat and engine, we had to prime the pump just to keep it going, turned out to be the fuel pump. The place where I bought it just switched it out and it worked great but the rest of the boat was garbage so I got rid of it , problem solved.

Post by **mikemicropterus** » Tue May 06, 2008 7:44 am

If the motor is under warranty take it to a dealer and let the merc warranty pay for the fix if not under warranty was it properly winterised...

It does sound like a fuel issue and with a fuel pressure gauge you could see the operational fuel pressure and if that is maintained...

To see if it is a bad fuel line, a vacuum guage is installed inline with the fuel line and ANY increase of vacuum will mean changing the fuel line

or you can geuss and play the change the parts game until it is fixed ...

A faulty fuel pressure valve will do the same thing and if it was not winterised properly this can be the result.....

Post by **curls** » Tue May 06, 2008 10:26 am

Thanks everyone. I mentioned these points to him and he's going to get a new tank and line - he wants a backup anyhow, just in case.

I hope this fixes his problem. If it's the pump itself - is that IN the engine?

Badger Shark: What didn't you like about the boat/motor? Just curious.

Post by **Badger Shark** » Tue May 06, 2008 11:45 am

I liked the motor though it was underpowered for the boat. The boat hull was great it was everything inside it that was garage, everything was put together like it was done on a Friday afternoon. All the screws in the boat would come halfway out if driving on a rough road or out in rough water. Bottom line is it was not very well built and I took it back and got the boat I have now.

Post by **curls** » Tue May 06, 2008 11:50 am

Funny you mention the screws... I noticed 3 screws that were 1/2 out, and one that was all the way out (which I guess my cousin placed in the cupholder and god that rattle was annoying until I finally foudn where it was coming from!).

Interesting take on it though, I'd have to partially agree except that I know they are value-priced boats that are strong, which is all I'd be looking for if/when I buy a boat -- something that will last hull-wise. I can tighten screws and use Loc-Tite. I cannot, however, weld aluminum

Post by **curls** » Mon May 12, 2008 10:47 am

Update:

It turns out it was a really easy fix afterall. The fuel connector at the engine was just slightly disconnected (about 2mm?) as there was a bit of grime at the end of the connector, preventing a full hookup of the line to the engine. My cousin cleaned it w/ a bit of fuel and a rag, and it positively clicked into place. Took it for a few rip this weekend and he says it was 100% fine.

Thanks for the help anyhow... and thank goodness it was a simple and free fix.

Post by **Haybay Larry** » Fri May 23, 2008 10:22 pm

Glad to hear that it was an easy fix!
I had a 17 1/2' legend for 16 years that was a Smokercraft hull. that boat was bullet proof The last 5 years I lived near Hay Bay and was on the water 3-4 times a week in allkinds of weather. It was the greatest boat I ever had- never leaked a drop. If I were to own a boat again I would look for another legend if they are still made by Smokercraft. They at one time were made by crestliner.
...Larry

Post by **Badger Shark** » Sat May 24, 2008 12:46 am

Larry they are not built like the old ones. The hull is fine, its everything else that is poorly done.

Post by **curls** » Sat Jun 28, 2008 9:14 pm

From my uncle who owns the boat:

Well, looks like the fuel line wasnâ€™t the problem after all. Itâ€™s doing the same thing, but I donâ€™t think it is a fuel line issue. When it starts sputtering after running for 10 minutes or so, I just shut off the engine, restart it and it works perfectly for another 10 minutes. No pumping the ball or anything.

Can anyone suggest something else to look at before bringing it in mid-season to a marina and having downtime?