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Mercruiser 496 Mag hesitation on top end

Mercury MerCruiser

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Old 06-29-2011, 12:59 PM   #1

sdf1jaj is currently offline
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My Model: Z275 Shabiah
My Engine: 496 Mag
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Default Mercruiser 496 Mag hesitation on top end

Hey all,
I have a 2001 Z275 Shabbah with mid-cuddy, and am running a Mercruiser 496 Mag with a Bravo III outdrive. Suddenly I have a slight problem that I need some help addressing. The boat comes out of the hole without a problem. I can hammer it, get on plane, then run for a bit without an issue. However, once it gets on plane and I start to trim up/throttle back, the motor has a hesitation to it. It seems to happen at about 3/4 throttle, so I'll ease off of it and throttle back into it then it runs fine and eventually does the same thing. It seems to act like a fuel-related problem, so I changed the water/fuel seperator and ran seafoam thru the tank. However the problem is still there? Any suggestions on what else I can try?
Thx,
Tony
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  • Old 07-02-2011, 03:09 PM   #2

    Stutterin_nate is currently offline
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    Default Re: Mercruiser 496 Mag hesitation on top end

    I had a problem where it would run fine then just die. turned out to be a loose ground on the slave solinoid. check your connections. you can also check the anti-siphon on the gas tank. there is a screen on it. maybe a tune up??
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    Old 07-05-2011, 05:45 PM   #3

    sdf1jaj is currently offline
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    Default Re: Mercruiser 496 Mag hesitation on top end

    Thanks for the info...I checked what I could and gave in...it's at the shop today but my mechanic takes care of me and I'm sure I won't have any bogus charges. I appreciate the reply!
    Tony
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    Old 07-06-2011, 03:23 PM   #4
     
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    darkcalling is currently offline
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    Location: Calgary
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    My Model: Z278 Limited
    My Engine: 502 Bravo III
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    Default Re: Mercruiser 496 Mag hesitation on top end

    Hi Tony
    Let us know what your mechanic finds that was abit of a toughy I was asking around with some of the guys around here no one had a good answer for it.
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    Old 07-06-2011, 03:35 PM   #5

    sdf1jaj is currently offline
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    Default Re: Mercruiser 496 Mag hesitation on top end

    Will do...
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    Old 07-18-2011, 03:32 PM   #6

    sdf1jaj is currently offline
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    Default Re: Mercruiser 496 Mag hesitation on top end

    After I took the boat to the shop they of course hooked their computer to it and found voltage error codes. Apparently my alternator was putting out about 13.2v and the 496 motor with 3 batteries on an isolator needs at least 14v. They sold me an alternator and we went on a test run after it was installed. The tech again hooked the computer up and of course it ran fine while he was on the boat. Took the damn thing out yesterday and it started hesitating again! I think it is a combination of the bad alternator that I had and also the batterires may need replaced. Of course the boat didn't have a problem while the mechanic was riding with me...figures. I'm going to put some batteries in the tihing and will let you know how it goes...
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    Old 07-18-2011, 04:52 PM   #7
     
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    Default Re: Mercruiser 496 Mag hesitation on top end

    Isn't that always how it goes I have been on both sides of that fence people bring me a car say its doing such and such we go for a drive nothing, they leave and call 3 blocks away say it's doing it again. Bring it back and there it is change part out and it's fine for a week then another issue. Have taken my vehicles in hooked to comp get all the codes change some parts fine for a day and bam codes everywhere again Good luck keep us informed.
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    Old 10-07-2011, 01:04 PM   #8

    sdf1jaj is currently offline
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    Default Re: Mercruiser 496 Mag hesitation on top end

    Ok, sorry for delay but been really busy. I replaced the alternator, a bad battery, and ultimately found that my fuel pump was going out. This of course was a job I wasn't going to tackle because the motor had to be pulled. So after all that, which I'm sure my alternator was bad and I needed a battery anyway, it was the high pressure fuel pump and ended up running my tab up a little. Oh well, she runs great now though!!!! Thanks everyone!
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