Mercruiser 5.7 Stuttering

[Norge]

My 5.7 Bravo III Mercruiser, Thunderbolt V ignition, is stuttering or choking.

I cruise & plane at 3200-3400 RPM. When I bring the power down or up to around 1600-2000 RPM, the engine seems to stall for 1/2 second - everyone onboard feels the pulse of the loss of energy. This happens randomly when at the right RPM. If I leave it there, it will continue a few times per minute. It seems like a sweet spot where this happens. It is right past idle or trolling speed (700-1200 RPM), somewhere where the bow will lift up, but not plane (256 Montery Cabin Cruiser).

This has been happening since last year. Otherwise the boat runs fine at low or high speeds. All I have to do is throttle up or down to stop the choking.

Last year I addressed the fuel - water seperator & some fuel additives - nothing.

This year - I just ordered a rotor & cap tune up kit, wires, spark plugs, & ignition coil.

Any other suggestions?

 

[Norge]

Re: Mercruiser 5.7 Stuttering

A year has gone by, the problem persists, and no replies???

After replacing the heads, manifolds, rotor & cap, tune up kit, wires, spark plugs, & ignition coil last year the problem continues.

The choking occurs at 2,000 rpms. If I leave it at 2,000 it will continue to choke, almost stalling. The rpms just jump up and down. I smell gas in the exhaust when this occurs. If I either give it more or less gas, the problem goes away. I think this year it is getting worse, but have no idea what to do.

Please help!

 

[cooter2506]

Re: Mercruiser 5.7 Stuttering

Go up to the adult only sticky and check the one thats says how to check your boats fuel system

 

[Fun Times]

Re: Mercruiser 5.7 Stuttering

A year has gone by, the problem persists, and no replies???

After replacing the heads, manifolds, rotor & cap, tune up kit, wires, spark plugs, & ignition coil last year the problem continues.

The choking occurs at 2,000 rpms. If I leave it at 2,000 it will continue to choke, almost stalling. The rpms just jump up and down. I smell gas in the exhaust when this occurs. If I either give it more or less gas, the problem goes away. I think this year it is getting worse, but have no idea what to do.

Please help!

What year is the boat/engine, And do you know the engine serial number?

 

[Norge]

Re: Mercruiser 5.7 Stuttering

1996 256 Montery Cruiser. However it is on it's 3rd engine, all replaced through warranty 7 years ago. Don't have the serial handy. But thanks for the two replies.

 

[Bondo]

Re: Mercruiser 5.7 Stuttering

Last year I addressed the fuel - water seperator & some fuel additives - nothing.

This year - I just ordered a rotor & cap tune up kit, wires, spark plugs, & ignition coil.

Ayuh,... That stuff is Annual maintanance,....

It does sound like a Fuel Delivery Issue,... Is this a Carbed, or Injected motor,..??

Btw,.... Sorry We missed ya last year,.... $h!t happens,...

 

[maxxman04]

Re: Mercruiser 5.7 Stuttering

was fuel FILTER changed?

 

[Fun Times]

Re: Mercruiser 5.7 Stuttering

1996 256 Montery Cruiser. However it is on it's 3rd engine, all replaced through warranty 7 years ago. Don't have the serial handy. But thanks for the two replies.

When you say replaced, Do mean they unbolted ALL the engine accessories off the varry first engine and changed the long block only then bolted on the old parts from the first engine, Or did mercruiser send you a 100% compleat new engine? The reason I am asking is there might have been a recall of some kind to the engine, And maybe it is just starting to show up now. Just a long shot to think about is all.

 

[Norge]

Re: Mercruiser 5.7 Stuttering

Motot replaced twice - short block & recycled accessories. Last year new heads, manifolds, etc.

Today I replaced the fuel pump & added some star brite additive. Idled good in the slip. I'll be fishing tomorrow morning & see if that worked.

 

[Norge]

Re: Mercruiser 5.7 Stuttering

New fuel pump & filter. Same problem. Can smell gas when it sputters. Would this be a carb problem?

Caught 5 keeper fluke today anyway!

 

[maxxman04]

Re: Mercruiser 5.7 Stuttering

might check to see if choke is operating correctly as well