1997 Mercruiser 5.7 Thunderbolt V Ignition cuts out for a split second while cruising

[h2o 4 play]

Newbie here, but I have been reading this Forum for quite some time and have found it very usefull and interesting.

Almost every time I head out on the water (engine is fully warmed up) once I rach cruising speed 2500 - 3500 rpm, the motor will cut out for a split second, I can feel it and see it on the tach. It only does this once per trip) I have checked all the connections and grounds thinking I would find a loose wire, but everything looks good. The engine runs fine, idles and accelerates great.

Has anyone had this issue before?

The ICM was replaced sometime by a previous owner, it now has 861253-1. It seems all TB V ICM have same Denso # 131800-7071

1997 Mercruiser 5.7, 2 bbl carb, TB V Ignition (no knock sensor) so I believe it to be 210 HP
1998 Baja Islander 180 (18 ft Bowrider)

Cheers

Peter

[Don S]

What outdrive do you have?

Before you start throwing a bunch of expensive parts at it, you do realize simple things like a faulty ignition switch, or kill switch, could cause your problem.
The reason I asked about the drive, is the plunger style shift interrupt switches on Alpha drives have been know to cause all kinds of intermittent running problems.

[h2o 4 play]

Thanks Don for the quick reply,

It is an Alpha One, I think it is a Gen II (I replaced the impeller last season and I seem to remember it was a Gen II)

[John_S]

I agree that it would be a long shot that the icm was acting in that unique way.

FWIW: The part number 861253T1 looks like it is for the 5.7L gen+ engine which is suppose to have a knock sensor and knock module. Not sure what it does to timing if they are not connected, but if it seems like your engine is low on power, check to see if you are getting full advance at wot. If not, that may be the reason.

[h2o 4 play]

I expected that my engine would have more HP (it was advertised as having 260 HP, but I beleive it is 210 HP), I was a little dissapointed when I first got it (my last boat had a 4.3 205 HP) My timing light does not have an advance feature, I will see about buying or borrowing one so that I can check the advance.

Does the Alpa Gen + have a plunger style shift interupt switch that I can test?

[John_S]

I expected that my engine would have more HP (it was advertised as having 260 HP, but I beleive it is 210 HP), I was a little dissapointed when I first got it (my last boat had a 4.3 205 HP) My timing light does not have an advance feature, I will see about buying or borrowing one so that I can check the advance.

Does the Alpa Gen + have a plunger style shift interupt switch that I can test?

I think you are confusing gen+ which is part of Mercruisers early vortec head engine model name, with the drive model name alpha genII. Your year engine should have an alpha gen II drive, which would have a shift interupter switch. I don't know what Don means about the plunger style, but I'm sure he will explain with a nice mecruiser manual graphic.

A '97 5.7L 2brl carb would indeed be 210hp. In '98 it was changed to vortec heads and 250hp. When that 210hp is not enough to keep you happy anymore, a set of vortec heads, new intake, and edel 1409 4brl, will get you to 280hp. Anything more, and $ will start to add up real fast.

[Eric.G]

Are you pretty sure that its cutting out and not a misfire?
I have a brand new 5.7 Gen+ crate engine that sounds like its is doing the exact same thing.
Over the course of two hours it will loose power for just a split second once or twice, but otherwise runs flawless.
At first I though like you that is was cutting out, but the more I hear it, I think its a misfire or a backfire that doesnt make it all the way to the carb.
Just a thought. I havent found a solution yet , but Im still breaking in the engine.

Eric