496 issue. intermittent.

[McRib]

Before the season started I had my boat serviced. Prior to the service the boat sat with about a half a tank and was treated with the typical treatments.

Had it serviced and was not told of any issues and the guy that did it said it ran fine on the hose. No biggie.

3 weeks later we made our first trip out to run it and make sure all would be well for DS. Backed into the water fired it up and everything was fine. Voltage seemed a bit low but the batteries are a couple of years old and had been sitting so I expected that. Idled around a bit to get the juices flowing and temp up to normal operating temp and eased into the throttle.

Under the load it spit and sputtered and backfired and fell all over itsself. I feathered the throttle a bit to try and work it out but it just kept doing it. I called the guy that did the service from the water and we spit balled back and forth with ideas and we both came to the conclusion that it most likely was a mix of old fuel in the lines and low voltage. No problem. I can see that. After about 20 more min of idling around I tried again. This time, everything was fine. Cruised around 40 mph and altered the speeds up and down. After being on plane and cruising for about 20 min the boat seemed to run perfect. No more falling all over itself at all. Boat ran great the rest if the day. After the weekend I packed it up and never thought about it again.

DS came and for 5 days the boat never skipped a beat. Full tank of fresh fuel and not one issue motor wise the whole time.

Went over 4th of July and Friday on the water the boat ran tits. Saturday till about 3 pm the boat ran tits. It was my first time back out since DS and Thurs night I put 54 gallons of fresh fuel in a 60 gallon tank. At around 3pm we were headed back toward the island and just south of steam boat while doing 45 or 50 it randomly started back firing. My buddy turns around from the bow and was like WTF is that? I back off the throttle a bit and it cleared up. Got back in it and the motor acted like nothing ever happened.

WTF do I have going on? What say the masses? It's an 05 496 mag with 320 hours on it.

Plugs are supposed to be "checked" at 300. Could my plugs be bad? Could this be an ECM problem? It's so intermittent I'm at a loss. If I took it to a mech I doubt they'd get an opportunity to duplicate the problem.

Whatcha got?

 

[McRib]

When I parked it at the end of the season there had never been any type of issue like this all of 2014.

On a side note.... in no way shape or form am I blaming the person who serviced my tub.

 

[Enen]

Have you priced out new plug wires for a 496? :yikes

 

[McRib]

Have you priced out new plug wires for a 496? :yikes

As a matter of fact I have. Lol

 

[tstone]

If you haven't changed the plugs yet I would recommend it. I recently had some of the same issues with my 496 and new plugs cleared it up completely. I'm not saying it will fix yours but it is probably the cheapest, easiest thing you can do . Good luck :thumbup:

 

[3queens]

I had similar issue and it was a plug wire came loose but not off the plug
On the pump side

Sounds electrical not fuel issue

 

[XX14]

When's the last time you did the plugs? They make a huge difference and it's a cheap place to start.

 

[HavasuHank]

Was this around the same time that it happened?

 

[GRADS]

I'm no expert but I've had a few 496HO's. I always thought the spark plugs were supposed to be changed every 100 hours. I would check that, the fuel filter and the fuel/water separator first.

 

[rrrr]

The stumbling was probably caused by ingestion of water.

Have you checked the water separator? Unscrew the filter/separator and pour it into a clear plastic container. You'll probably see a half inch or so of water and crud on the bottom of the liquid.

Change the filter. Important: Start the engine and check for fuel leaks!

 

[djunkie]

I'd get someone to put a scan tool on it first and see if anything comes up.

 

[McRib]

When's the last time you did the plugs? They make a huge difference and it's a cheap place to start.

I've never done the plugs. The book says they are 300 hour plugs. Obviously with me being at 320 I'm leaning toward this heavily. Just seems to simple of a fix. I definitely gotta get them done though just based on the fact that I've exceeded the "life" by 20 hours.

 

[28Eliminator]

Fuel pressure/filter maybe? Since it sinking with some old fuel in it, maybe it's clogged up the filter with some crap...?

 

[McRib]

The fuel water separator filter was changed during the service in march. Do you think it clogged that fast? 3 tanks of good fuel have been through it since the service.

 

[McRib]

FYI the only fuel filter I have is the one on the motor behind the sea pump. I don't have an in line one from the tank to the separator.

 

[XX14]

My Rage needed them badly at 260 to the point where it wouldn't getting on plane coming off the trailer but then it would finally clear up and run fine. Did the plugs three seasons ago. No wires and its run great ever since. Definitely worth a try. The plugs I took out didn't look horrible either.

 

[rrrr]

The fuel water separator filter was changed during the service in march. Do you think it clogged that fast? 3 tanks of good fuel have been through it since the service.

It's not clogged, there's just water that got into the tank from condensation. The right combination of temperature and humidity can produce water on the empty portion of the tank, and it sinks to the bottom...where the fuel pickup is.

Don't make things overly complicated. Don't take it in for service. Don't spend money. What you described is exactly what happens when a bit of water is sucked into the fuel system. The engines complains for a second, and then it runs normally again. If it was plugs or wires or the ECM or whatever else everyone guesses at the problem wouldn't have been a momentary occurrence.

Take five minutes and dump out the filter/separator contents. You don't even need to change it. Just make sure the gasket is seated and there isn't a leak. You know why that's important.

 

[McRib]

Don't make things overly complicated. What you described is exactly what happens when a bit of water is sucked into the fuel system. The engines complains for a second, and then it runs normally again. If it was plugs or wires or the ECM or whatever else everyone guesses at the problem wouldn't have been a momentary occurrence.

Take five minutes and dump out the filter contents. You don't even need to change it. Just make sure the gasket is seated and there isn't a leak. You know why that's important.

I'll check that the weekend after next for sure.

 

[McRib]

Anyone have a part number for the plugs? For those who have changed their plugs... did you do the 20$ per merc plugs? Did you get the cheaper ones from a GM dealer? Anyone have luck with parts store over the counter equivalents?

 

[McRib]

It's not clogged, there's just water that got into the tank from condensation. The right combination of temperature and humidity can produce water on the empty portion of the tank, and it sinks to the bottom...where the fuel pickup is.

Don't make things overly complicated. Don't take it in for service. Don't spend money. What you described is exactly what happens when a bit of water is sucked into the fuel system. The engines complains for a second, and then it runs normally again. If it was plugs or wires or the ECM or whatever else everyone guesses at the problem wouldn't have been a momentary occurrence.

Take five minutes and dump out the filter/separator contents. You don't even need to change it. Just make sure the gasket is seated and there isn't a leak. You know why that's important.

View attachment 418809

Mine does not look like the one in yore picture. Mine is the cartridge type held in by 3 bolts and has a handle to pull up on. It more of a screen cartridge.

 

[rrrr]

Like this? None of the 496's I have owned had this one but I guess the procedure is the same. If there's water in the housing pick it up with a rag?

I'm almost sure you have a bit of water being sucked into the fuel system.

[video=youtube;8m7qNw1sWcA]https://www.youtube.com/watch?t=18&v=8m7qNw1sWcA[/video]

 

[McRib]

Like this? None of the 496's I have owned had this one but I guess the procedure is the same. If there's water in the housing pick it up with a rag?

I'm almost sure you have a bit of water being sucked into the fuel system.

View attachment 418810

Yes. Exactly this type. I'll pull it my next trip out and check it for sure. I've done my own services before so I know how to check it. That won't be an issue

 

[Cray Paper]

As mentioned, sounds like water in the fuel, if it was ignition related it wouldn't be as intermittent. You can check the plugs wires with an ohm meter, if there in spec they are good to go. When you do change the plugs, don't skimp, same as water pumps, starters, alternators and any other accessory you count on. The cheap lifetime guaranty crap gets old when your constantly breaking down / getting stranded and or wrenching on stuff to keep it working. Ignition components fall in to this same category.

If the stock part lasted 100k miles or more / 300 hours or more why gamble on stuff you know wont last as long.

 

[XX14]

Regardless the plugs need to be changed. My neighbor is a GM mechanic he got me the plugs for pretty cheap. Not sure of the number.

 

[Mandelon]

Change the plugs. Had the same issue with my lavey at about the same hours. The change fixed it.

One weekend it was fine, the next...I needed plugs.

Never had any fuel and water problems.

 

[natedog]

Change the plugs

 

[McRib]

Change the plugs. Had the same issue with my lavey at about the same hours. The change fixed it.

One weekend it was fine, the next...I needed plugs.

Never had any fuel and water problems.

I'm gonna buy them for sure. According to the manual I'm 20 over anyway. Anyone have a hook up on them?

 

[Mandelon]

http://teaguecustommarine.com/em0011/spark-plug-mercury-496-ho.html

 

[Mandelon]

PN: ACD 41-993
SPARK PLUG - MERCURY 496/HO
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Availability: In stock
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Quick Overview
AC DELCO Spark Plugs: , stock #41-993.


AC DELCO Spark Plug for Mercury 496/HO Engines. Replacement for Mercury # 33-863622001.

Gap @ .060 for Mercury 496/HO



SOLD EACH




AC Delco Professional Platinum Spark Plugs are ideal for engines that run on conventional plugs and newer engines that require platinum plugs. ACDelco Professional Platinum Spark Plugs can give you up to 100,000 miles of service before requiring replacement.*

Professional Platinum spark plugs also feature:


* Dual platinum tip for improved resistance to spark erosion, fouling, and corrosive combustion chamber environment

* A platinum center electrode and a platinum pad lower the ignition demand voltage

* One-piece integral suppressor seal helps reduce radio frequency interference, meters spark plug energy to help provide long electrode life, and seals against
compression leakage

* Designed with corrosion-resistant shell

* Spark gap remains virtually unchanged during the life of the plug
Spark Plug - Mercury 496/HO

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Details
AC DELCO Spark Plugs: , stock #41-993.
AC DELCO Spark Plug for Mercury 496/HO Engines. Replacement for Mercury # 33-863622001.
Gap @ .060 for Mercury 496/HO

SOLD EACH

AC Delco Professional Platinum Spark Plugs are ideal for engines that run on conventional plugs and newer engines that require platinum plugs. ACDelco Professional Platinum Spark Plugs can give you up to 100,000 miles of service before requiring replacement.*
Professional Platinum spark plugs also feature:

* Dual platinum tip for improved resistance to spark erosion, fouling, and corrosive combustion chamber environment
* A platinum center electrode and a platinum pad lower the ignition demand voltage
* One-piece integral suppressor seal helps reduce radio frequency interference, meters spark plug energy to help provide long electrode life, and seals against compression leakage
* Designed with corrosion-resistant shell
* Spark gap remains virtually unchanged during the life of the plug
Additional Information
Model ACD 41-993
Manufacturer AC DELCO

 

[McRib]

Are the delcos what I have from merc? Anyone know what brand they are that they command 20 bucks a piece??

 

[McRib]

If Teague pushes delcos they gotta be good, right??

 

[ColdSteel]

Anyone ever use Iso-Heet for water in fuel?

 

[Always Floored]

If you can't figure it out, just sell it and buy a new boat.

 

[Vegaskeith]

Your engine is fucked! Better pull it out and stab in a 525!

 

[Mandelon]

AC DELCO PROFESSIONAL PLATINUM SPARK PLUGS #41-983 /QUICKSILVER #33-863622
Mercruiser 496 Mag HO and Other Also GM -GMC TRUCKS ETC

You don't have google on your computer?

 

[Mandelon]

service bulletin allows for an AC 41-983 gapped to .060.

 

[McRib]

I don't need Google when I have mandygoogle

 

[Mandelon]

Sheesh, do I need to pick them up and put them in for you too? :skull

 

[McRib]

service bulletin allows for an AC 41-983 gapped to .060.

983 993 952 blah blah blah. I've found 4 different part numbers on line for the delcos. Which one is the right one for an 05 496 mag with the cartridge type fuel filter ??? Apparently there are two types of 496 mags. :grumble::grumble:

 

[McRib]

Sheesh, do I need to pick them up and put them in for you too? :skull

Yeah! U coming out for the mcraftup? Lol.

 

[Activated]

If changing the plug doesn't work...wait for it...maybe try a different prop.

Fuck, I was waiting for someone else to chime in. :smackhead

 

[rrrr]

Instead of spending $200+, I would do the free inspection of the separator.

Yeah, the plugs might need to be changed, but the symptoms you described point to water in the filter assembly.

I always check the simplest things first.

 

[ACS]

I Cross referenced the stock plugs on my 496 ho and put in E3 spark plugs 4 seasons ago. Checked them last weekend and still looked perfect. You might want to check those out.


The motor has had a Procharger on it for the last 11 years (rebuilt in 07) and have never had a problem with plugs.

 

[McRib]

Instead of spending $200+, I would do the free inspection of the separator.

Yeah, the plugs might need to be changed, but the symptoms you described point to water in the filter assembly.

I always check the simplest things first.

If it is water wouldn't it do it more often? The cartridge is not very big. If there was enough water in there to be a problem I'd think it would be happening more often. I'm checking it no matter what. I'm just asking.

 

[McRib]

I Cross referenced the stock plugs on my 496 ho and put in E3 spark plugs 4 seasons ago. Checked them last weekend and still looked perfect. You might want to check those out.


The motor has had a Procharger on it for the last 11 years (rebuilt in 07) and have never had a problem with plugs.

I'll be checking all of it out for sure. Gonna start with the fuel separator and probably will buy plugs cause I'm at 320 hours anyway.

 

[ACS]

Filter and plugs. Always start with the simple( cheap) things first.

 

[DaveC]

here you go McRiblet

http://ww2.justanswer.com/uploads/ROCKETBOAT/2008-12-09_042519_SPARK.pdf

I just bought some from Amazon

 

[McRib]

here you go McRiblet

http://ww2.justanswer.com/uploads/ROCKETBOAT/2008-12-09_042519_SPARK.pdf

I just bought some from Amazon

Thanks bro

 

[Warlock1]

If it is water wouldn't it do it more often? The cartridge is not very big. If there was enough water in there to be a problem I'd think it would be happening more often. I'm checking it no matter what. I'm just asking.

Not necessarily. If the water and gas sits for a period of time they will separate into neat layers. However when bouncing around such as in a boat they will tend to separate into bubbles for lack of a better term. Think of cooking oil and water in the same container. So most of the time the pickup was sucking fuel or at least mostly fuel and at some point grabbed a large bubble of water and there is your stumble.

Your doing the right thing by changing out the plugs because that is a known condition and then you just work on the unknowns that are quick, easy and cheap first. By the time were done with you, you will have a rebuilt engine with a Whipple on top.

 

[Ziggy]

Your doing the right thing by changing out the plugs because that is a known condition and then you just work on the unknowns that are quick, easy and cheap first. By the time were done with you, you will have a rebuilt engine with a Whipple on top.

And a regelled keel