Carver Owners Forum

Hi,

My starboard transmission on my 405 is noisy. After reading all of the great posts here, I decided to start with the engine and make sure it is running right before proceeding further aft. I replaced the cap and rotar and the replaced the plugs. I made little wooden rack so I could put the removed plugs in the correct sequence for inspection. After removing them I found a website that offered pictures of spark plugs in various conditions. (after removal). Obviously from comparing mine to the pictures, all are showing rich. They are basically black and smell like fuel.

Now, what might be the cause of black smelly plugs? I have read that things like fuel injectors, throttle body, wrong plugs, wrong gap......and various other things. We have owned the boat for about six months and are fixing things one at a time.

The engine runs and idles OK, although our marina mechanic says he can feel it vibrating when he puts his hands on the risers.

All ideas are welcome....thanks

Proper reading of spark plugs takes a little time....the engine would have to be up to operating temp and the plugs removed and checked after a run. If the " ground strap" is sooty that could be just overly rich idle...where you check colour is on the white ceramic down in the centre......correct timing can also be checked by looking at the marks on the ground strap.......so a little more info , was the engine just run cold at the dock then plugs out ????...that could be misleading IMHO...... :beer good:

Have a look at this it may help a bit hopefully....http://www.4secondsflat.com/Spark_plug_reading.html

All the things that bud37 says are important. Dark plugs could just be a red herring from how it was recent run (cold, idle, etc).

Ruling all that out though... then:

What engines?

I would not suspect injectors if all the plugs look the same. Much more common for them to be partially plugged, due to the screen or buildup, and causing the engine to run lean. Do you have a 4bbl throttle body? If so, then I'd suspect if 1/2 the cylinders are affected then MAYBE it's injector-related, but that doesn't sound like the case.

Could be something as simple as a temp sensor... do you have a dedicated temp sensor for the ECU, vs what shows up on the guages? Is this a closed-loop system (has O2 sensors) or open loop? I suspect open loop, given the rich condition, or I'd suspect O2 sensors if it was closed loop...but then again it would only affect one bank.

Ok...the link that Bud37 sent me is fascinating...never knew spark plugs could reveal so much.

Second, I'll have to do a little research to answer the second set of questions. The engines are Mercruiser Horizon MPI's 454 1998 version. The plugs that came out are AC Delco MR 43T's. A friend told me that they might be to cold for this engine??

Thanks...

There are several things that will cause the noise. You're on the right track in that you should first confirm the engine is running properly before assuming something wrong at the tranny end. If the engine is shaking, it could be that one or more cylinders aren't firing, improper combustion, timing, fuel quality, sensor failure, fuel delivery issue, ignition problem, etc. Tough to say without further diagnosis but you're on the right path by getting your ignition system back to spec so you can eliminate that system as the culprit, and it's a regular maintenance requirement anyway.

I can double check but I'm pretty sure MR43T is what should be used.

This is not a catalyst application so CO sensors do not apply.

Is the noise always there no matter what rpm you're at, in gear, out of gear, fwd, rev? Does the engine hunt at idle? Does rpm drop for a bit like it's going to quit when you throttle up from idle? Does the engine start no problem and stays running or does it take a couple of tries? Does it fire, run then stall a couple of times before you finally get it going? Have you checked your tranny fluid, is it clear red? Does it have a burnt smell? Is it at the proper level? Has this vessel ever had an impact?

Hi Viper,

As you can tell from my previous posts, I'm fixing my list of things on this boat. I finally figured out the CO detectors and several other things, now for the starboard engine.

It starts and runs fine. Usually turns over once and is running. It has never died although during the sea trial it did die once but has never done it again. It does not surge but as above our local mechanic seemed to think he could feel it vibrating slightly.

I'm replacing the plugs with NGK R BR6FS gapped at .035. I have read that the high energy ignition system should be at .045. I think there is a placard on the engine specifying the gap. I'll use whatever it says.

I will say that when we took possession of the boat, we ran it 65 miles up the Cumberland River (here in Nashville) without a problem.

The noise is more evident in gear at idle than at other times. As the RPM's come up it gets somewhat quieter. The surveyor said he thought it was because the trans was actually turning opposite to the other transmission. I'm a retired airline pilot and seems to me that both sides should sound the same, at least that was important in airplanes. During the survey the running gear was closely examined when the boat was out of the water and thought to be OK. If it has hit something in the past, I'm not aware of it.

The transmission fluid (velvet drives) is red with only a slight oil smell not would I would think of as burnt at all

So, I'm thinking that either the engine isn't idling at it's best or the damper plate is shot. There is an observation hole that is covered with a rubber plug and I was wondering if with a bore scope one can see the damper plate? I have a friend who has a wiz bang piece of equipment...lights, camera and the works. Might look at the plate before jumping into something that doesn't need to be fixed.

Thanks for all the help with the CO detectors, the radar and now this! I love working on this old boat and this forum has been a lifesaver. Hopefully with everybody's help, I'll have it up to my standards by boating season.

Those two plugs are the same.

405driver wrote:Source of the post ... The surveyor said he thought it was because the trans was actually turning opposite to the other transmission......

That's news to me.

The flex plate is definitely a consideration.

The MPI rpm is ECM controlled but out of curiosity, what rpm is it idling at in neutral, and what happens to the rpm when you put it in gear? Too low can cause tranny rattle.

i also noticed the same on my plugs when i bought my boat thinking a rich condtion on all my plugs. i have moved up one temp range hotter on my plugs. i have the crusaders not the mercs engines i dont know what kind of use you will put on your 405 but alot of the time my river cruising is 2200 rpms or less.

Are we dealing with a throttle body here? If so, have we cleaned the sensors within? Or do they need replacing. Sensors tell the ECM what is going on and then the ECM compensates. My '98 crusaders TB's need cleaning periodically with carb cleaner and a toothbrush. Mike

Viper et al,

I'll check the idle RPM next time we go out and report back. Seems winter has returned to the Southeast for now.

How do you figure out what a "hotter" plug would be? Guess I can Google that.

I'm not familiar enough with throttle bodies to take that on as a project. I have read that they can certainly cause issues. I would bet that these have never been cleaned. Any references as to how to clean them would be appreciated.

I'm going to change the plugs and check out the idle etc. If it's all within parameters, think move on back to the flex plate and see if I can check that out without taking anything apart. Will advise.

Thanks everyone, all great ideas.