Boat Broke Down-Advice/Help w/ repair

[Blue Water 23]

Well this is horrible timing. I want to get my boat up by my week off next week.

I have a 20ft. Blue Water with a 4.3 liter Mercruiser inboard/outboard. It is about 9 years old. I was trolling the W on Saturday from about 2:00 until 6:00, with the big engine. I picked everything up and headed back up to Meldrum Bar. The boat ran fine all day until the run upriver. After about 5 minutes of running close to full speed the boat started losing power. It would lose a little power and then go back up. It did this a few times getting worse and worse. I then pulled back the throttle and it almsot shut down. I then turned it off. There was a little smoke coming out of the spark arester. I got towed in. All of the gauges were fine. The temperature was fine, the oil pressure was fine, etc.

I started it up in the driveway Sunday morning with the hose attached. It ran perfect with no problems. We headed to the river. It started fine but it was nocking, right under the water pump. It nocked when it was idling, and then it nocked faster as the engine sped up. We headed out. About 5 minutes into the run downriver it started losing power again. It acted just like if you pulled back on the throttle for a couple of seconds and then put it back down. It did this a few times getting worse and worse. We slowed it down to a troll and it ran fine. He went just faster than a troll on the way back and it ran fine going that speed, except for the nock that was just below and behind the belts. From the bottom front of the engine (Maybe from the crank shaft). Again all of the gauges were fine and the engine didn't seem hot. The oil looked fine.

I don't know what could be wrong with it. Here are the different things that I have heard;

A vapor-lock in the fuel line

Something wrong in the distributer; I would think that this would make it mis-fire or back-fire.

The fuel filter, Does it even have a fuel filter? Or would it be in the seperater?

This is getting me depressed. I don't have unlimited funds but I do want to have my boat for next week. What do you think could be wrong? Do you have any suggestions? Should I take it to a normal mechanic? A marine place? Any help would be great.

Thanks, Jesse

[Salmonator]

Fuel pump?

[Blue Water 23]

Would that make it knock? I was leaning towards thinking that it was in the fuel system.

[jet]

Coil

I had the same motor and I lost the coil and your symptoms sound the same. The seam to go out slowly.

Or a clogged fuel water seperator.

Jet~~~

[Salmonator]

Take an old wooden broom handle and cut it to make a three foot or so section. With the engine running put the rounded end to your ear and the other end onto the part of the engine that you think is producing the knock. Be very careful, you don't want that stick to kick back while it's against your head. But this will give you a very good idea of where the sound is coming from. If I remember correctly, a mechanical pump will give a knocking sound when it is on the way out. The fact that you are losing power when the fuel demand is at it's highest is another indicator. But just a guess regardless...

[BlueWater]

Jesse,
It sounds to me like something else but this is a possiblity. I have a 19' BlueWater with a 4.3 and when I first got mine it would cut out and start sputtering all the sudden when I was out and about I could not figure it out. To make a long story short if you look at where the motor cover meets the transom you may notice that the distributor and coil are directly below the seem and are very prone to getting wet. I riged up a flap over the distibutor and moved the coil so they did not get wet anymore and the problem was solved.

Hope this helps.

BlueWater.

[Blue Water 23]

If there was a problem with the coil or the distributor would that make it miss or back fire? It isn't doing that. It is just like if you pulled the throttle back and it got less gas.

If it was the fuel/water seperator would that make it knock?

I have been thinking about this for about 24 hours straight and can't figure it out. Thanks for all of the suggestions so far.

[YaHoeeFishOn]

The fuel pump is electric on this engine. The timing chain is behind the water pump. Is knocking at crank speed or cam speed ? Cam and lifters are 2x crank speed. Colapsed lifter clack or click. Rod Bearings knock .

[Ivana Fishalot]

they actually use water as a knock suppressor because it cools the heat combustion down.

You really need to check the flow and pressure that your fuel pump is delivering. A knock comes from a lean condition which is exactly what it sounds like is happening.

[Seefood Man]

Coils are a weird one . Sometimes they will go out without any warning and times they will lose their ability to generate enough spark to to get a full burn. Also they can generate a "slow spark" which would explain the misfire and smoke.
BTW always leave that flame arrester on! The up side is that coils arn't very expensive to replace. Good Lock

[Blue Water 23]

It sounds like the coil or it's in the fuel system.

How can I check to see if it is in the fuel system or the coil? Is there a way besides to just start replacing things?

Again, thanks for all of your help so far. At least I have an idea now.

[YaHoeeFishOn]

water in fuel ? clogged or full water/gas seperator ? Starving from gas ? carbon tracked distributor cap ? arking coil wire ? I'd give her a new fuel filter and check cap rotor .
how loud is knock ? loose bottom end sounds. piston slap , rod bearings , wrist pins . Cam lifter sounds. To hard to quess over a terminal .
How many hours are on engine ?
need to verify fuel ,carb , ignition problems before going after major mechanical. My 4.3LX GMC 262ci v6 rattles a bit , my 93 19ft BlueWater Overnighter has 450 hrs on it.

[Blue Water 23]

I would guess about 400 hours or so. The knock is just loud enough to hear over the engine with the engine cover closed.

About how much is a fuel pump? Should I just change it or is there a way to check it?

What would I see if the coil needs to be replaced? Or should I just replace?

It would be nice if there was a way to know if it was a fuel problem or not to know where to start on replacing things. Is there a way to tell?

[River Kid]

I had a 3.7 liter Mercruiser that performed radically like what you discribed. It also had a knock that would come and go. Took a long time to identify the problem. One day at idle it just shut-off. Turned out that the woodruff key (half moon shaft key) had sheard. That key locked the timing gear to the crank. So after shearing, all that turned was the crank, but no top end of the motor. For a long time I was constantly re-timing the engine before it finally sheared. When it was partially sheared, the crank was shifting in relationship to the cam, valves, etc. Years earlier I had hit rocks with the outdrive, and evidently only partially sheared the key. Wasn't to bad to fix, never had to break open the engine, just tore into the timing cover and pulled the pulleys.

[russdogedog]

I might have a fix for you. there is a one way valve on the gas tank sometimes the spring go's bad or it could have a peice of hose getting in the way.

[YaHoeeFishOn]

there was a recall on the fuel pump wire harness connector. The new one has a orange dot on it if its been replaced. Do you know if the fuel pump plug was ever recalled and replaced on your engine ?

[russdogedog]

I might have a fix for you. There is
a one way valve on the gas tank sometimes the spring go's bad or something in the valve that not letting enough gas to flow to motor.

[Blue Water 23]

If I was going to take it to a mechanic where should I take it? Would they just start ripping it apart and start replacing things or would they be able to tell what the problem is? Any mechanics on here that do side work?

[Fish-n-Fever]

Go online to Iboats Join (free) ask any ? you like in the proper forum. There are many mechanics that read and answer ?'s on that page.
Ron

[Seefood Man]

Hold on a minute! FIRST pull the spark plugs and let us know what they look like OK. Don't go "parts replacing" Find the problem. Also, this might better addressed by Boat Doc.

[All Wet]

I don't know anything about boats but if that engine was in something with wheels I would pull the fuel line where it connects to the carb or injector block, put the end of it in a can or jar and crank the engine a couple of time and see how much gas I got. Rolling stock usually has a filter between the gas tank and the fuel pump. Also some carbs have one right where the fuel line connects. I would also check for a water seperator. Some need repaced and some just need dumped and dryed out. It does sound as if it is getting more air than fuel. Also most auto parts places sell a gadget (cheap) that you just hold in your hand and place around the spark plug wires one at a time. It will light up each time the plug fires. A mechanical fuel pump that is bad could make a knock. Try the simplest things first. Good luck.

[YaHoeeFishOn]

a fuel pump is 160-180 dollars. My 93 did have a recall for the connector on the fuel pump.
861155A6 FUEL PUMP 805656A2 $188.10 $160.49