Fouled Plug (S)

[1Holeshot]

My 200 Pro XS 4.6 ( serial number in sig ) with only 62.5 hours started missing and shaking. Stopped and started again and same thing and barely able to plane off. Today I took it to dealer who connected to computer and told me indications of misfire was found. Removed plugs and they had a fair amount of carbon fouling on them. Replaced plugs and tested boat on lake and performance was back to normal. I questioned dealer as to why the engine would have fouled plugs so soon. Explained that I use 87 Octane non ethanol and also use Seafoam in recommended amounts.
I do not do a lot of idling graphing or any other time except in no wake zones. Fortunately ours are not very long. Dealer said it is very important to run full throttle for a few minutes each trip especially on the return trip to help burn off any accumulated carbon. I run some full throttle most trips but fully expected a set of plugs to last longer. My older 2.5 litre 2 strokes would run several years without fouling plugs. My 4 stroke auto engines do not run full throttle ever and the plugs last many thousands of miles.

Anyone else with the 4.6 Mercury outboards fouling plugs with low hours?

[DaveTTN]

I never saw it on mine but I use a mixture of mercury quickclean, Lucas fuel treatment and marine stabil in every tank. Also I tried to always have a 5-10 minute run at wide open throttle per outing.

[1Holeshot]

Eliminate the additives and run the E10 Top Tier fuel. It has all the cleaning components you need formulated into the fuel.

Mike, I know the owners manual recommends top tier 87 Octane fuel which is 10 % Ethanol here. Do you run Ethanol free gasoline in your engine?

[mikesxpress]

No. Never have.

[Pulsare2020]

I changed the plugs on my 300R due to skipping around 55 hours. They old plugs actually looked good. I noticed I had 3 plug wires from the factory that did not "snap on" as well. The new plugs solved the skipping for about 30 minutes. Don rectified the issue for me and found a defective injector harness wire to #7 cylinder causing an over rich condition (not only on that cylinder) and also installed a new set of plug wires under warranty. I have about 15 hours on it since the warranty work with no issues or skipping. I run non-ethanol and use Don's "cocktail" now.

[1Holeshot]

Thank you to all who have replied. I appreciate your insight and experience and will be using Top Tier E10 87 octane gasoline going forward.

[DaveTTN]

I don’t know that I agree with running ethanol gas unless your using a tank of gas every week or two. Personally I always use ethanol free 100% gas with a minimum of Don’s cocktail. Following that regimen I have never had a fuel related issue since 2010.

[1Holeshot]

Good point Dave.
I run ethanol free in my lawn care equipment and have been using in my outboard because the fuel usually sits for more than two weeks. Aware of the risk of phase separation in ethanol/gasoline mixture.

[EuropeanAM]

Guys- take a look at the FAQ Section here in the forums. Tried, tested and true recommendations can be found there.

I do not recommend the "forget additives" approach. Being pushed progressively by several, but I can tell you first-hand from working with the injectors that it DOES make a difference.

Anyone that actually sees the internals of engines and the injectors on a regular basis will understand this.

Back to the original topic: There are several factors that can cause this. Keep in mind, running the engine at WOT (100% Demand Linear) does NOT "clean" the engine. As a matter of fact, it's potentially just the opposite in many cases.

The engine runs it's "cleanest" where it gets it's best fuel economy. AND where the engine's Advanced Range Optimization strategy kicks in and helps to optimize the fuel consumption.

The fuel octane being run can play a role, as can RPM range utilization, additives (or lack thereof), climatic conditions, and even how well the engine is PROPPED.

That last one is a common thread... if your engine isn't propped to get up into the 6100-6200 RPM range at WOT, you're overloading/lugging the engine most (if not all) of the time.

[thommo59]

I just changed my plugs at 60 hours, 1 year. They were fine at this stage and I understand this is early however, my 2 cents is every year, plugs, engine oil, filters etc. I just believe this part of owning a boat and good insurance for a good day on the water.

[1Holeshot]

Guys- take a look at the FAQ Section here in the forums. Tried, tested and true recommendations can be found there.

I do not recommend the "forget additives" approach. Being pushed progressively by several, but I can tell you first-hand from working with the injectors that it DOES make a difference.

Anyone that actually sees the internals of engines and the injectors on a regular basis will understand this.

Back to the original topic: There are several factors that can cause this. Keep in mind, running the engine at WOT (100% Demand Linear) does NOT "clean" the engine. As a matter of fact, it's potentially just the opposite in many cases.

The engine runs it's "cleanest" where it gets it's best fuel economy. AND where the engine's Advanced Range Optimization strategy kicks in and helps to optimize the fuel consumption.

The fuel octane being run can play a role, as can RPM range utilization, additives (or lack thereof), climatic conditions, and even how well the engine is PROPPED.

That last one is a common thread... if your engine isn't propped to get up into the 6100-6200 RPM range at WOT, you're overloading/lugging the engine most (if not all) of the time.

Thank you Don for giving facts by someone who sees the internals and injectors on a regular basis. I absolutely appreciate this and other advice you have provided to me and other owners of the 4.6 Mercury engines.

It looks like I need to prop down a little because neither of my props will turn over 6K rpms and that is in cooler weather.

Another thing I need to change is running a full tank of fuel when unnecessary. Most of my trips only take about 10-12 gallons or less. The extra weight can contribute to overloading/lugging my engine and hurt fuel economy.

[Maine-Basser]

I had 3 of 8 plugs foul with only 35 hours. Boat would not get on plane that day. Dealer replaced all 8 and was able to cover under warranty.

[Trent R]

I fouled my plugs at 60 hours. Same symptoms that you reported. I suspect I sucked some moisture thru the motor running in very poor weather conditions. Thru air intake

[dave540]

It is the non ethanol gas that is fouling your plugs. Some will say that isn't it but I have a 1965 Nova with a 540 BBC engine and Holley Sniper fuel injection and MSD HEI ignition and I was running non ethanol gas and fouling plugs every couple of hours. I also have a 1965 Belair with a 327 and it was fouling plugs at about one hour. Swapped everything on the 327 from a known good engine with no change. I was stumped. I have a friend with a 434 Ford (351 based) Mustang race car and he was running the same gas as I was and fouling plugs every five eighth mile races. Like me, he tore everything off the top of the engine trying to find the problem. No success. He called me one day and said that last night laying in bed, he had an epiphany. He said the only thing in common all these cars had was the same gas being used. He said that he emptied what was left in his 2 gallon fuel cell and spilled some in his driveway. It evaporated but left an oily spot in his driveway. He also noticed that when he went into the top of the engine, that it had an oily substance coating the inside of the intake manifold and the intake ports of the heads. We both started using 93 ethanol gas and no longer foul plugs. If you google non ethanol gas and fouled plugs, others have also had this problem. Some brands of non ethanol gas may be OK but the brand I was running was Liberty.

[SilverFox579]

I don’t know that I agree with running ethanol gas unless your using a tank of gas every week or two.

I do and don't burn a full tank in months let alone a couple weeks. My '09 Optimax, 1B722937, has been run with 87 octane top tier ethanol obtained from a high traffic station 3mi from my house since NEW. It routinely sits a couple months or more between outings (hasn't been in the water since March) but I keep the tank FULL and EVERY drop of fuel that goes in the tank is treated with Quickleen and Quickstor in addition to the Optimax specific recommendation of PP at 150:1. My lawn equipment, including 2-stroke saws and trimmers, gets the same fuel treated with Quickstor only.

I, too, have never had a fuel related issue and, in fact, the pulse fuel pump in my engine has never been replaced.

[EuropeanAM]

Gary- I can tell you that your engine was designed and calibrated for 87 Octane E-10, Top-Tier fuel.

That's what will run/perform best.

See the Fuel and Fuel Additives post in the FAQ section for more details.

[1ranger487vs]

Not a 4 s but I have always used e 10 in my engines. No problem. Sometimes it will sit a month. Never fill up each tank. Maybe 10 or 12 gallons at a time. I run a water separated and it never has any signs of water in it when I change it once a year. I do run ringfree in my Yamaha and now in my opti. Was using 89 but just switched to 87 and didn’t notice anything. Never ran ethanol free gas.