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496 ho hesitation?

Old 02-08-2014, 11:02 PM
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Default 496 ho hesitation?

Hey Folks,

I am brand new here tonight. Hoping you can help out. I am the original owner of a 2003 Formula 260 Sunsport with a 496 HO/Bravo III drive, with approx 530 hours on the engine.

Running great, but….over the past year or two, a couple things have come up.
1) overall, just seems to be getting slightly tired. Still runs great, but my hole shot and top speed are slowing a bit. WOT RPM does not seem to get there anymore always and if it does, it seems to take longer to get there. Any overall suggestions on what to do here? no alarms and running good other than just a "feel" of lower power, etc…
2) the bigger issue is…over this past summer (summer of 2013) we've noticed periodic and regular hesitation. It happens at pretty much any RPM…it will be running fine, and then periodically, it feels like the boat slows for a few seconds and then takes off again. It's not serious or violent, but just feels almost like you encounter some drag periodically. It happens regularly (maybe 1x or 2x every minute) and then goes away. There are no alarms on the engine, but you actually do notice a change in engine sound and actually see the rpms slightly drop.

Could this be a fuel filter, the IAC, fuel pressure regulator, fuel pump, or something else?

Any suggestions on what to look at would be greatly appreciated!!

Thanks,

Greg
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Old 02-09-2014, 11:24 AM
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Probably a cylinder dropping out intermittently. Replace the spark plugs. That is most likely the problem. Might try getting injectors cleaned also. I bet that will get you back to running right.

Bob Lloyd
Full Throttle Marine
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Old 02-09-2014, 11:38 AM
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Start with spark plugs, and probably plug wires too.

Do you have, or have access to a Rinda scanner?
If the IAC is bad, it will probably be throwing a code, but not always. Common fault on 496s, BUT does not fit your symptoms.
You can check the range of all the sensors as opposed to just waiting/hoping there is an alarm along with a fault.
Also, you can induce misfires and do a full injector test with the Rinda scanner, which really helps in troubleshooting.
Do a search on Rinda Scanner here on OSO; it's weight in gold for any Mercury motors MY2000s and later.

I bought ethanol fuel once when I was under the impression it was not. I left the fuel in the boat for 5 months, untreated in the FL humidity.
When I fired it up in May, the ethanol fuel ruined my inline fuel filters, F/W separators, AND my low pressure fuel pumps. Idle fuel pressure was fine, but anything over 1000 rpm it was all downhill; on BOTH motors.

Do you have ethanol fuel? Do you treat the fuel to negate the bad effects of ethanol?
How long have your fuel/water separator been on there, and the inline fuel filters? (Your boat more than likely has the inline filters as I have a 2003 boat with 496s and it's rigged with them, per Mercury specs of that time frame.)

When my low pressure fuel pumps came out, they rattled they had so much junk in them.
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Old 02-09-2014, 11:58 AM
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I chased a similar problem for a while. Iac, plugs, wires, ECM, dead cell on a battery, can all be culprit. In my situation it turned out to be a pinched coil wire. A scanner does make it easier to remedy. I enjoy the rinda tool I own.
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Old 02-09-2014, 12:05 PM
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Thanks everyone!

I'll definitely try plugs/plug wires as a starting point for this season.

I don't have a rinda scanner, but have been considering it. This is probably what I needed to actually go and get it.

I don't believe my marina has ethanol fuel, but I'll confirm when the season starts again this year. Always buy from the same marina and until now, never had problems.

I think it might be time for a new fuel filter and fuel water separator. I honestly don't recall the last time I had either of those change.

So…it looks like my plan of attack for this season is:

1) replace spark plugs
2) MAYBE replace spark plug wires
3) replace inline fuel filter
4) replace F/W separator
5) also potentially get the injectors cleaned

thanks again!

Greg

Last edited by gsmikla; 02-09-2014 at 12:12 PM.
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Old 02-09-2014, 12:10 PM
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Good point on the battery as mentioned by dlange.
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Old 02-10-2014, 07:45 AM
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Check the booster fuel pump screen. Mine was clogged with crap and had a high speed hesitation. Located by fuel separator.
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