Vyper340

Replace the crank position sensor. It will not show on the diagnostic as failing but Merc has had several problems with them. They are cheap ($40) and it's an easy, fast fix.

mats

As stated before, check fuel pressure all the way up to WOT and especially in the situation when you have the miss above 4500 rpm. Any fluctuation indicates a problem with the fuel supply. Could be the pump, the fuelpressure regulator, the filter,the fueltank vent, the antisiphon valve, the fuellines or that the system is sucking air somewhere before the pump.

fountain27ho496

My merc. tech thought the same thing, fuel pressure.
They agreed to go for a ride next week with the scan
tool and a fuel pressure gauge. It better malfunction
then. I'll post the results. I'll get out this weekend and
see if I can find anything simple. In the cold and rain,
most likely. It did run 69, on the speedo, which is the
best it has ever run, before it started missing. JC

boatfreak

Any news?

SHAKEN Not Stirred

NGK plugs #BR7EFS or the new NGK
number is 1094

$ 1.99 each at Sparkplugs.com

Monarch Products 909-672-8501

CJG.

Indy

The guys with the electrical comments might be on the mark. I was reading my Merc manual for the 496HO last night and it stated that if there is voltage problems, the ECU will reset, most of the time it resets so fast it seems like the engine misses for a sec. For what it's worth...

fountain27ho496

Still waiting for these guys to go for a ride, too busy.
I wish my business was so good I could put people off.
But then boating is more fun than new carpet.
Are those the correct plugs for 1.99?
The manual says they last 300 hrs any way.
I'm going to stop in and talk to them today, I'll mention
the elec. problem. This a common problem with this
package? Thanks again, hopefully I'll have some news
soon. It might get warm someday. 55 and raining.
I'm selling everything and moving.JC

CigDaze

Thanks!
Where did you find that P/N cross reference?

Sparkplugs.com didn't list anything for marine applications, but if you look up a GMC truck with the 8.1L(same plugs? I don't know...), they range from like 4.99 to 14.99

SHAKEN Not Stirred

I actually got the new part number while trying to find plugs on a Sunday in Lake Havasu. The Napa Auto Parts guy found the cross reference, then advised that they didn't stock them.

I told him he should bring a few dozen or so in as the folks with the 496's will be looking for them soon.

I then spoke to the guy at SparkPlugs.com, Monarch Products and he confirmined the same 1094 part number.

I've changed the plugs a few times as I'm running the Whipple blower on the 496 MAG HO.

Regards,

CJG

CigDaze

Thanks a million...!!!
I assume you noticed no difference in performance...because I can handle 16 bucks...

When the guys at the Merc authorized parts center said calmly, "That'll be $122.88 with tax," I about had a stroke...I said he can keep 'em.

Thanks again!