2003 496mag running issues

[nordic454]

Picked up our 2003 Cheetah Fast Cat with a 496mag last June. Had 121 hrs on it, and now has 142hrs.
It fires up every time with no hesitation, idles perfectly. As soon as I start to put a load on it to get on plane, it struggles. Always seemed like a fuel issue. I would change the fuel/water separated filter, and after a few minutes on plane it would clean out and run great the rest of the day. This season it has been progressively getting worse to the point where I could barely get on plane yesterday. Once on plane it continued to run rough and bog down when I tried to add more throttle. I am thinking spark plug issue. The transom has a lot of soot on it from only running maybe an hour total including idling. It is acting like it is getting flooded when I add throttle. If the plugs are going bad, or one is fouled, would that cause his type of running issue? I have brand new batteries, changed the oil in March, and changed out the fuel/water separator filter yesterday morning before going out. I also filled the tank all the way full last Sat before going out.

 

[AzGeo]

SPARK PLUGS . Take a few of them out . SHAKE the spark plug, end to end . It will rattle, and that is because the built in resistor is burned out of it .

Buy 8 new plugs, gap to spec, tighten them GOOD . Go boating ..........

 

[nowski]

If all else fails, try changing the small disc style filter that is located underneath the water separator filter. I had an issue 2 year ago and my boat seemed to be starving for fuel. I finally threw in the towel and took it to Hallett, Jim Frisbee changed that little disc filter and put all my problems to bed...

 

[nordic454]

I've heard of that disc filter, but have no idea what or where it is. Can anyone shed some light on it for me?

 

[nowski]

I've heard of that disc filter, but have no idea what or where it is. Can anyone shed some light on it for me?

When you pull the filter and filter cup out you'll see it at the bottom of the fuel supply module. Is that a Gen III Cool Fuel Module were talking about?

Here is a disc filter I found on Amazon to give you an idea what your looking for...

http://www.amazon.com/MERCURY-MERCRUISER-QUICKSILVER-MODULE-FILTER/dp/B01AX8R15U

 

[nordic454]

When you pull the filter and filter cup out you'll see it at the bottom of the fuel supply module. Is that a Gen III Cool Fuel Module were talking about?

Here is a disc filter I found on Amazon to give you an idea what your looking for...

http://www.amazon.com/MERCURY-MERCRUISER-QUICKSILVER-MODULE-FILTER/dp/B01AX8R15U

I don't think I have that type of filter. My water separator/filter is a screw on oil filter style canister. Unless it's in a different spot. Forgive me, I am still new to this type of motor setup.

 

[Outdrive1]

You have one or the other. They are located next to the sea pump. If you have the screw on filter you don't have what they are talking about.

 

[nordic454]

You have one or the other. They are located next to the sea pump. If you have the screw on filter you don't have what they are talking about.

Thanks... Feel dumb. Lol

 

[Hypnautic]

'04 496. Your symptoms seem very similar to what I experienced. Ultimately it came to new fuel pumps. Cannot remember if it was the low or high side fuel pump-- changed them both while they were in there. In the second pix you can see the disc filter. Mechanic said it is typical for those not to be replaced since they were moderately expensive. Also notice the water in the fuel...

 

[Runs2rch]

The stock 41-983 plugs are platinum. They are not that great. The stumble is as George said from the plugs. Run NGK TR55IX iridium plugs. Much better plug overall.

 

[nordic454]

I am going to replace he plugs regardless seeing as they are 13 yrs old. I have an inline fuel filter between the tank and the water spectator and pump that I am going to replace. We'll see where that takes me

 

[Outdrive1]

I am going to replace he plugs regardless seeing as they are 13 yrs old. I have an inline fuel filter between the tank and the water spectator and pump that I am going to replace. We'll see where that takes me

Prime the new filter. I usually fill them at least half way up with fresh gas or sometimes it can be a bitch to get it started.

 

[nordic454]

Prime the new filter. I usually fill them at least half way up with fresh gas or sometimes it can be a bitch to get it started.

Yessir. I appreciate the help

 

[Runs2rch]

I am going to replace he plugs regardless seeing as they are 13 yrs old. I have an inline fuel filter between the tank and the water spectator and pump that I am going to replace. We'll see where that takes me

The inline filter has just a screen in it. You can pull it and clean it. Made to filter tree branches I guess. The newer motors they stopped using them.

 

[AzGeo]

I am going to replace he plugs regardless seeing as they are 13 yrs old. I have an inline fuel filter between the tank and the water spectator and pump that I am going to replace. We'll see where that takes me

Remember to 'shake' the old plugs, as you remove them . (end to end) You will hear and feel a 'rattle' inside the plug . That is the 'burned out resistor material' and giant gap missing from inside the plug .

These plugs 'fire twice', as this engine has a 'wasted spark ignition system', so they actually have twice the run time as you would expect V8 spark plugs to have . (fires near TDC, and near exhaust valve opening event)

YES, NGK iridium or better ........

One or both of your fuel filters should be '10 microns or less' in filtration size, for EFI .

 

[Runs2rch]

Remember to 'shake' the old plugs, as you remove them . (end to end) You will hear and feel a 'rattle' inside the plug . That is the 'burned out resistor material' and giant gap missing from inside the plug .

These plugs 'fire twice', as this engine has a 'wasted spark ignition system', so they actually have twice the run time as you would expect V8 spark plugs to have . (fires near TDC, and near exhaust valve opening event)

YES, NGK iridium or better ........

One or both of your fuel filters should be '10 microns or less' in filtration size, for EFI .

Yeah buddy. I just did plugs in a 496HO. Same off idle stumble. New Ngk Tr55IX. Wham Bam!!! :thumbsup

 

[LargeOrangeFont]

I like the standard copper TR55 plugs myself. Change them every other season.

 

[Runs2rch]

I like the standard copper TR55 plugs myself. Change them every other season.

You can do this also. The iridium plug longevity is great for boaters that forget to change plugs. OP said these are 13 years old.

 

[SBMech]

142 hours and the plugs are shot?

That would seem like a manufacturing defect to me with platinum plugs on a fuel injected motor.

Good thing we got so many people who have seen this stuff to help give advice, I learn new shit everyday around here :thumbsup

 

[Runs2rch]

142 hours and the plugs are shot?

That would seem like a manufacturing defect to me with platinum plugs on a fuel injected motor.

Good thing we got so many people who have seen this stuff to help give advice, I learn new shit everyday around here :thumbsup

No matter what engine I have pulled platinum plugs out of they always have more deposits on them than they should. Proper heat range. Depending on the application I either run standard copper V power Ngk's or Iridium Ngk's. I have never had a plug issue with either.

Copper is better for performance but you will need to change them very frequently, perhaps every 10k. Here are some of the thermal conductivities of some commonly used metals (Watts / centimeter*Kelvin). As you can see, copper is untouchable. Iridium gives you the best trade-off between performance and lifespan.

Zinc = 1.16
Aluminum = 2.37
Copper = 4.01
Steel = 0.70 - 0.82
Platinum = 0.716
Iridium = 1.47

 

[SBMech]

Yea, I swear by NGK.

It's amazing how much better things run with a decent plug in the proper range. :thumbsup

 

[nordic454]

And this is why I came here for advice...

 

[guest hs]

Change the spark plugs if you still have a problem do a fuel psi test and a scan on the engine your engine does not have the gen III fuel system so no filter disk on yours just the water separator. If you replace the water separator buy a bottle of Mercury Quickleen fill the water separator with that and then start and run the engine.

 

[Runs2rch]

I forgot to mention. I run Lucas in every tank of fuel. The complete fuel system treatment.

 

[Andy B.]

I forgot to mention. I run Lucas in every tank of fuel. The complete fuel system treatment.

Didn't realize my mechanic has been putting Lucas products in my engine for the past four years and I noticed more rpm and better fuel economy go figure!!

 

[nordic454]

So I just changed out my spark plugs. They were AC Delco plugs that were in there. I installed NGK TR55ix. I did not hear any rattling in the old plugs as I removed them. A few of them looked ok, a few of hem looked pretty ugly/dirty. The #5 cylinder plug was pretty wet. I will change the fuel/water filter and fill it with Quickleen on Thur when I can get it on the hose and run it for a bit.

 

[Runs2rch]

Problem solved!

 

[nordic454]

I hope problem solved.
As far as this Quickleen goes. It says to only add 1oz per 5 gallons. Ive got a 20 gallon tank, 4oz just doesn't seem like much to me to do anything. But because of that, I am a little wary to fill my filter up with it, and run it as I don't want to hurt anything.
Anyone with experience with the stuff, if you've got some advice it would be appreciated

 

[nordic454]

Input the recommended 4oz in the tank, and put about an oz in the filter, primed it, and fired it up an the hose. Let it run about 5 minutes or so. Purred like a kitten. Never noticed the nice idle lope the 496 has until it's actually running properly. Once it warmed up a touch, I bumped it up to 1500, then 2000 then 2500 ramps and it was nice and smooth. Then revved it up a few times and it rapped up quickly, very quickly, and smoothly.
The real test will obviously be when I get it on the water Sat and get it under a load. But so far seems to be running great.

 

[Runs2rch]

The quikleen is pretty concentrated. I run a few different additives in my truck that 1 oz treats 30 gallons.

I just changed plugs in a 496ho the other day. Same issues you were having. Plugs looked the same. Purrs now.

 

[nordic454]

Took the boat out on the lake yesterday and WOW!!! Is all I can say. That did the trick. This is the best she has ran since I bought her last summer. It is amazing, and kind of sad just how neglected this boat was in the service department. But sometime you always have bugs to work out when you buy something new, and it's just a matter of getting your hands on every aspect of it so you know exactly what you have.
Thank you to everyone for the suggestions and help. Now we can enjoy the summer!! Mama even learned how to drive it. I haven't fought her this boat yet, because it's been temperamental when it want to run right.