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496 Down - Please offer any advise

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Old 06-04-2009, 02:29 PM
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Default 496 Down - Please offer any advise

I have a 496 Ho that is giving me some grief. Had it out twice this season with no issues then all the sudden its stalling out on me to the point I am having to be towed in. First time it died I just came off a 5 miney run at about 4500 rpm. As soon as I throttled off it cut out

It will fire up and run on idle for at least 5 minutes, once I try to give her some gas to get going it cuts out and stalls. It will then turn over but not fire for about 5 –10 minutes. After resting/looking at the fuel filer a few times, etc.. it will fire back up then the same thing all over again. Will run great at idle on the dock, keeps good temp and oil pressure.

I have changed the water separator and checked fuel. In a glass jar looks very clean. I also tested the fuel pump out of the boat. When I hook it up direct to a battery it fires and pumps well. I also hear it prime in the boat, but am not sure what its doing after it fires.

Any idea what other basics to look at before I have to get the merc certified guys involved??

Last edited by JBoat; 06-04-2009 at 02:56 PM.
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Old 06-04-2009, 02:59 PM
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I had a similar issue with my 496. It was under warranty so the dealer fixed it. I didn't troubleshoot (or know how) but apparently there is a low pressure (idle?) and high pressure (running?) fuel pump on the 496. So 2 pumps. My boat would run great at idle or very low rpm's but the minute I hit the throttles it died. They changed the pump and its been great for 2 seasons. Maybe this helps?
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Old 06-04-2009, 03:14 PM
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Actually after looking at the fiche online I make have 3 pumps. The one I tested was the external pump coming out of the fuel filter.

I also see the high and low preasure ones you refer to in what they refer to as a fuel module.

Not sure I can locate that unless its on the intake and I do see it under the cover.

Does this motor have a sensor that is driving these pumps? If so is it easy to get to?
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Old 06-04-2009, 05:26 PM
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There are two fuel pumps on the 496. Depending on the year you have...

Earlier ones have:

One behind the spin on filter which is the lift pump. This pulls fuel out of the tank and greatlys assists startup if run dry.

The other one is on the port side of engine right behind/below the motor mount (KoolFuel).

The newer ones that have the large black box on the starboard side of engine also have two pumps but the filter and pumps are enclosed in that housing.

If you think you have a delivery problem just put a pressure tester on the rail (large schrader valve under the coolant tank). Stock setting is 43 psi.
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Old 06-04-2009, 06:57 PM
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Great design, you basically have to move the coolant resevoir to attach your pressure guage to the shrader valve. There is also a filter in that fuel module that should be changed, that is if you have the newer style with the fuel module.
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Old 06-08-2009, 03:22 PM
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OK - So I may not have a fuel problem. Bleed the fuel rail out cold and their was no air just gas squirting out. Fired it up a few times in and out of RPM and had 55lbs of fuel pressure all the way threw. 55 lbs Seems high but its a Tyler Crocket motor so I am sure some thing is hoped up a bit.

The motor cuts out after about 10 minets of running while maintaining fuel pressure. Guy I know with a 496 keeps telling me a crank position sensor. What do you guys think ?
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Old 06-08-2009, 03:35 PM
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Sounds similar to what happen to mine last year. Idle fine at the dock everything looked good putted down the river out into the open waters gave it a little gas got about halfway on plane and it died. restarted tried again same thing. got back up into the river stoped to change the fuel water seperator and couldn't get it to fire back up. Funny site watching a little 12 ft aluminum boat with two big old boys pulling us up stream. Tow cost $10.00 and a 12 pack of labats. yes my 496 has the two pumps low pressure high volume to get the fuel up to the high pressure pump. Turns out my low pressure pump was not working. get some one to assist and touch the pumps while they turn the key to the run position. You should beable to feel them both running.
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Old 06-08-2009, 03:36 PM
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Quote:
Originally Posted by JBoat View Post
OK - So I may not have a fuel problem. Bleed the fuel rail out cold and their was no air just gas squirting out. Fired it up a few times in and out of RPM and had 55lbs of fuel pressure all the way threw. 55 lbs Seems high but its a Tyler Crocket motor so I am sure some thing is hoped up a bit.

The motor cuts out after about 10 minets of running while maintaining fuel pressure. Guy I know with a 496 keeps telling me a crank position sensor. What do you guys think ?
My experience with crank sensors is they either work or don't typically not an intermittent issue with them
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Old 06-08-2009, 03:37 PM
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Quote:
Originally Posted by JBoat View Post
OK - So I may not have a fuel problem. Bleed the fuel rail out cold and their was no air just gas squirting out. Fired it up a few times in and out of RPM and had 55lbs of fuel pressure all the way threw. 55 lbs Seems high but its a Tyler Crocket motor so I am sure some thing is hoped up a bit.

The motor cuts out after about 10 minets of running while maintaining fuel pressure. Guy I know with a 496 keeps telling me a crank position sensor. What do you guys think ?
Crank Sensor triggers it's code. No reason to throw parts at it cause someone says "that's it". Put a scanner on it and find out if that's it. If the sensor failed it will tell you. I've also seen crank sensor codes that where not the true culprit. The scanner will tell you where to start...
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Old 06-08-2009, 04:10 PM
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Quote:
Crank Sensor triggers it's code. No reason to throw parts at it cause someone says "that's it". Put a scanner on it and find out if that's it. If the sensor failed it will tell you. I've also seen crank sensor codes that where not the true culprit. The scanner will tell you where to start...
Damm Marina is telling me 2-3 weeks before they can even get anyone down there to scan it. To bad you can rent a scanner online somewhere. Or can you ? Maybe its a good business to start.
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