Mercruiser 5.7 engine stalls when when shifting to idle or gear. Will not restart

[bcox777]

I recently purchased a 95 Larson Escapade with a carburated mercruiser 5.7 engine and mercruiser out drive. The engine was replaced last week prior to me purchasing and when I try to water test the boat I am able to run the boat in neutral with some throttle but when I take the throttle back to the middle point where it should idle and move to gear the engine dies. From this point when i try to restart the engine, it just turns over as if it were flooded although i did not give much additional fuel when attempting to restart. If I wait about 10 - 15 min, it fires right away and continues to run but still can not shift to idle or gear without stalling.

I would take this back to the mechanic or the guy who sold me the boat but neither will return my calls over the last week. So looking to the forum to assist and will try to work this out on my own. Thanks for your assistance.

Brian

 

[Fishermark]

Re: Mercruiser 5.7 engine stalls when when shifting to idle or gear. Will not restart

You don't mention which Mercruiser outdrive you have. It is an Alpha? Sounds like you may have a shift cable that is bad. If that is the case, it is activating the shift interrupt when going into gear and causing the engine to die. Have someone look at the switch to see if it is engaging when you shift.

You may have other problems as well, but that is where I suggest you start looking.

 

[bcox777]

Re: Mercruiser 5.7 engine stalls when when shifting to idle or gear. Will not restart

Yes I believe its an Alpha but will need to double check. Would the shift interrupt also cause the immediate restart issue?

 

[petermarcus]

Re: Mercruiser 5.7 engine stalls when when shifting to idle or gear. Will not restart

Yeah, that's a pretty classic sign of a shift interrupt problem, which is usually caused by the cable.

When you're putting the drive into gear, there's a little switch on top of the engine that cuts out half the cylinders for a fraction of a second. It helps the gears mesh without stripping them. When the cable goes bad, it holds the interrupt open, so you're basically not getting spark to half the engine and it's impossible to keep it going.

I had the same thing once (on a Larson coincidentally, but it happens with many Mercruisers) and fixed the cable and it went away. Sometimes, I could wiggle the throttle and it would free the cable up then the engine would start again, but it's a losing battle until the cable is fixed.

 

[Bondo]

Re: Mercruiser 5.7 engine stalls when when shifting to idle or gear. Will not restart

Ayuh,... I agree the lower shift cable is probably the Issue with shifting into gear....
But,...
Not being able to Idle, is most probably a Carb issue...

 

[Fishermark]

Re: Mercruiser 5.7 engine stalls when when shifting to idle or gear. Will not restart

Yes I believe its an Alpha but will need to double check. Would the shift interrupt also cause the immediate restart issue?

I agree with Bond-o that you have other problems as well.... but it could still be the cable. My last boat had a situation where the shift interrupt would get in a bind and stay engaged - so the engine would not restart. But if that were the case, it would not start after 10 or 15 minutes either. Not until you wiggled the shift lever and the switch would spring back.

But - this is easy to check. Simply look at the shift interrupt switch and see what it is doing while someone shifts. If you aren't sure where it is, ask. Someone will post a picture or a link to the manual.

 

[petermarcus]

Re: Mercruiser 5.7 engine stalls when when shifting to idle or gear. Will not restart

Here are a couple pics from mine (I have a 3.0L, but it should look pretty much the same).

When shifting back and forth, just before it goes into gear, it should basically "pop" on and off pretty quickly. When mine stuck, I wasn't able to idle either. I'm guessing your 10 or 15 minutes just allowed the cable to relax. It will shut off half your engine until the cable frees itself again. Normally, this switch is on top of the engine. My carb is up, the stern is to the left, mine switch sits on the valve cover. In a V8, it might be between valve covers.

(Ignore my hand, these pics were for my reference during my engine teardown. The second pic shows the switch itself with the cable removed)

 

[petermarcus]

Re: Mercruiser 5.7 engine stalls when when shifting to idle or gear. Will not restart

A little more clarification, since I've had this problem with both Mercruisers I've owned, and it is fairly common. I hope there's some use to anyone in the same situation. In this pic:

When the boat is put into forward or reverse, that triangle of plastic moves up and down (in the pic -- starboard and port in the boat). When it goes the blue way, the switch contact moves fore and presses the button on the switch (yellow arrows). That cuts off your cylinders and allows the gears some time to mesh. It should pop right back to the center, which releases the switch and you get your spark back. The other gear direction is the green direction. I can't remember which is forward and which is reverse, but one is each way. If your engine stalls after putting into gear, or trying to switch gears, or sometimes just putting it into idle, you might notice that the switch arm isn't nestled squarely into the center of those notches. They might be right up on either hump, or part way down the sides. You might be able to wiggle it and get it in and try to start the engine again.

It could be the switch itself that's bad, which isn't hard to repair since everything is right there on top. It's often the cable, which is harder to fix because it's hard to replace the cable without removing a lot of parts in the way (at least in my 5.0L Mercruiser).

 

[paultjohnson]

Re: Mercruiser 5.7 engine stalls when when shifting to idle or gear. Will not restart

Hey guys wouldnt it NOT only not start, wouldnt it NOT crank at all if it was the shift interrupt switch? I thought it was either all or none ? Plz enlighten myself as well.... Thanks.... post paddn Paul

 

[petermarcus]

Re: Mercruiser 5.7 engine stalls when when shifting to idle or gear. Will not restart

The shift interrupt kills the spark to the cylinders (half of them on a V8). It doesn't kill the power to the starter or anywhere else on the boat. So, you'll be able to try to start the motor and the starter will crank (chug-chug-chug), but it'll never catch, because half the cylinders aren't sparking. It'll flood nicely, and if you're stubborn, you'll drain the battery and it'll never start (but, if you pop that arm back in the center and wiggle the cable, it should start up again, assuming it's not too flooded).

I learned a lot of this the hard way through trial and error, about 3 miles offshore. Then when I was back home, I found what was going on through several iBoats forum posts