Replacing Spark Plugs

[WChapelle]

I have a 1997 330 Sundancer. It's been running fine until yesterday when it seemed to be running a little rough. I purchased the boat in August of last year so basically I have one about one years use. I'm wondering if changing the spark plugs would help. At least that seems like the least expensive first step.

 

[Lazy Daze]

You could, but if the prior owner recently did that, it would be wasteful. Do you know the maintenance history... or can you find out?

In lieu of that, pull a couple plugs and look at them - see if they look alright.

Can you be more descriptive about "running rough"? The more detail you can give, the more we can help. Diagnosing via a forum is tough to begin with, you know? :smt001

PS: Put your engine model in your signature.

 

[WChapelle]

No, I don't know the maintenance history, I think the boat sat for a season or two before I purchased it last summer. The guy who did the survey said they were ok.

It's just seem to be running as smoothly as it did a few weeks ago. It just seems a "little heavy".

I'm also a little embarassed to say I'm sure of the model.

I have Mercruiser, 300 HP. The Seriel numbers are OK 261060 and Ok 261059. I think they are 7.1 but to be honest I'm not sure. I saw on another thread that you can tell by the seriel number but not sure how to do that either.

I don't mean to be such a dolt, but this is all new to me. I guess ya gotta learn somehow.

 

[WChapelle]

While reviewing my survey report I see that it has 454 Ci, I assume that means cubic inches. Is that 330 hp per engine? Maybe that's why the model is a 330. I thought it was because it's 33 feet long.

 

[Lazy Daze]

No worries at all - like they say... the only dumb question is the one you don't ask.

It's just a funny coincidence that the number on your engine (330) is the same as your boat's length. If I'm guessing correctly, you also have stern drives, as opposed to V-drives? I think the V-drives were rated about 10HP more.

The way that engines were rated, up to about the mid-90's was confusing. They used to rate the HP at the engine (would show a higher HP). Then, they started showing two ratings - the second one at the prop. Eventually, they now only advertise propshaft HP. The "330" you saw could mean different things, especially since your survey shows 300HP. But, to be sure......

There were a couple of models of 454's (454 cubic inches or 7.4 liters). To see which one you have (which will tell us, among other things, whether you have 300HP or 330HP), you can do a little investigative work to find out what type of fuel system you have... Carb'd 300HP, EFI 300HP(Electronic Fuel Injection... AKA Throttle Body Injection, or was it 310HP, I'm not sure), or true fuel injection (MPI... Mulit Port Fuel Injection 330HP).

First, pull the flame arrestor off (one bolt, 7/16" I think). Underneath that, you will be looking at where the air enters the engine (this is the throttle body). If you see plastic/metal (old yellow plastic and goldish metal in color) things with a couple wires attached, you have EFI.

If you see funnel looking devices (metal and no wires), you have a carb'd engine.

If you see nothing, you should then have MPI... but to be certain, you can find the gas line coming from the tank - it will go to a fuel/water filter on the bottom/front/starboard side of each engine. This filter may/may not have a black plastic box around it. The box is about 5" or 6" across and a maybe a little taller. Once you find that, follow the gas lines as it goes to the engine. It should eventually split and go to 8 individual fuel injectors.

If you have to "pump" your throttle control lever to start the engine, that typically means you have a carb'd engine. But, sometimes a carb'd engine can start w/o doing that so it's not always indicative of carb'd or fuel injection.


Now, back to your problem. Does the roughness ever go away at different RPM's/loads?

Here's where I would start.... When was the last time the fuel filters where changed? If you're not sure when they were changed, that should be done regardless of whether or not they are the problem. They should be changed at a minimum of once a year. Preferable more, but it depends largely on fuel quality/fuel tank condition and whether or not you use a fuel additive like Startron, or not.

Sorry for the long winded response, it just takes a lot of words to get across some simple things sometimes. :smt101

 

[Quint4]

All good advice from Dennis as usual. I will add the 7.4s are known to be hard on plugs...(so I've heard and mine likes new plugs). I would swap them all to establish a "baseline" of known good parts. The correct plug should be listed on the cover on top of your engine. this will give you a good opportunity to get up close and personal with your motors and have a good look at plug wires, dist. cap., etc.
you can get plugs at NAPA for way less than at the dealer.

 

[WChapelle]

I have v drives (inboards). And the fuel filters were replaced whtn I but the boat in the water in the spring. And, I have carbs, not FI.

I'll take a look at the plugs this coming weekend.

Thanks, this is great information.

 

[Lazy Daze]

OK, sounds like a plan. Let us know about the RPM's/load thing when you get a chance, too.

Is this happening on both engines?

Even though the filters were replaced this spring, never discount the possibility of needing to be replaced again. Especially with ethanol fuel (if you're using that). Do you use an additive designed to combat ethanol and keep the fuel fresh? Unscrew one of your filters and dump it into a clear, glass jar. Let it sit for a few hours (on a stable surface on land) and see what it looks like.

The problem could still very well be plugs, but fuel is always a great place to start for problems like this.

Since you have V-drives, reverse the location I told you about for the filters... meaning you'll have to crawl around the backside/sternside (which, actually, is still the "official" front of the engine since that's where the belts are).

 

[Dick Whetstone]

I recently had a similar problem on my 7.4. If your engine "miss" started rather abruptly and is rythmic" (sp??), I would suspect a spark plug, the distrubutor cap, or (as in my case) a bad spark plug wire, which according the the local Sea Ray Dealer, almost never happens. If the engine spits and sputters at random, I would suspect a fuel system issue.

 

[WChapelle]

I called my marina this morning. He suggested that we first check the bottom before we do anything with the engines. I keep the boat on Tilghman's Island on the Chesapeake Bay, we have lots of growth this time of year and he wantes to make sure that's not the problem, which it may be.

Sometimes it sits for a couple of weeks at at time so between growth and barnicals (sp?), even with bottom paint, it can affect my performance. I'll let you know what I discover.

 

[sbw1]

No, I don't know the maintenance history, I think the boat sat for a season or two before I purchased it last summer. The guy who did the survey said they were ok.

On a boat this age and with an unknown maitenance history you should consider changing all the belts and hoses, plugs, impellers, spark plug wiring harnesses, filters and all fluids and risers. Then you know what you have and can start doing maintnenance according the schedule.

 

[Lazy Daze]

I'm not sure I understand your mechanic's logic (and I am NOT one, so he may very well know something I don't) behind growth on the hull and an engine running rough.

Unless... In your second post you re-described the problem as "heavy". Do you mean to say the engine is running smooth, but just doesn't have the "get up and go" it used to? If that's the case, then yes, more drag on the hull bottom will certainly cause a loss of performance.

Is it both engine's?

 

[WChapelle]

Dennis, thanks for staying with me on this one. Once he mentioned the growth option it seemed to make sense to me based on the way it felt "heavy". I did miss speak in that the engines didn't feel like they were missing but it sure seemed hard to push the boat through the water.

I have changed all the fluids and recently the impellers.

So, let's see what he finds and I'll let you know if a good power wash is the fix. I should know in the next day or so.

Bill

 

[Lazy Daze]

Sounds good, Bill. That does seem to make more sense.

Like SBW1 said, "starting fresh" is a good idea, too. Not that you have to do it right now, but just think about it for next season.