Mercruiser 3.0 shaking and loud tapping noise

[vroom ZOOM]

Hello

Went out the first day of the season on my boat, it has a 2000 mercruiser 3.0 with an alpha one. Before going out I pulled the drive and checked the alignment, bellows, gimbal bearing, splines and u joints. all looked in spec and when I put the drive on it popped right in with one hand. I took it out for a drive today and it started right up, idles great, no stalling so I revved it up and was ready to have a nice time on the water BUT i heard a loud tapping/ almost banging noise. I slowed down, took the engine "doghouse" cover off, and let my brother drive the boat while I watched. At about 3800 rpm the noise started and the motor shook violently side to side. the noise came from the coupler area I am pretty sure. At higher rpms it worked well again. It was the same kind of shaking just when you are cranking the engine and it fires the first time and gives a big jolt, like seen in this video of me starting it the first time this year:https://www.youtube.com/watch?v=RtZao36fUwY

 

[vroom ZOOM]

:bump2:

 

[tank1949]

U may have fouled a plug or maybe bad plug wire. 20 year old boat? When was last time tuned up? Pull and examine. Distributor cap may be cracked too or burned buildup on contact tips inside. When did you change fuel filter? Looks like clean fresh water boat.

 

[vroom ZOOM]

Yeah that might be a good idea. I put a new coil, cap and rotor in it recently, but never changed the plugs or plug wires (its an est system). Also last year I drained the water from the filter and cleaned it. when the shaking started it doesn't seem like there was any loss of power at all, it was pulling smooth and I wouldn't have noticed it if someone sitting near the back didn't notice it.

 

[vroom ZOOM]

also is it normal to have that whine (you can hear it in the video when I rev it up) and is it normal for the engine to shake like that on startup?

 

[tank1949]

also is it normal to have that whine (you can hear it in the video when I rev it up) and is it normal for the engine to shake like that on startup?

It has been my experience that alternator/belt causes whine, but I only have experience with Chevy V8s. Maybe 3.0s are different. Running it w/o alternator belt on for a few moments would eliminate or identify it as an issue. Good luck. I'd replace fuel filter. Fine crap will dam it up. I assume your filters are water separators as well? Unlike cars and trucks, boats normally set unused for months and crap accumulates as gasoline breaks down into varnish and ethanol "eats" rubber and seals. Sorry.... That's just they way it is. I bought a used boat one time that I had to recycle a full tank of gas through filter to remove trash.

 

[vroom ZOOM]

Now that I think about it, what you are saying makes sense that at higher revs there's not enough fuel and it starts misfiring. I'll give that filter some tlc right now, but the funny thing is that there is NO reduction in power when the shaking starts!

 

[vroom ZOOM]

Ok, update now. I put new plugs in, but it wasn't that easy. First two went out easy, third one was very tight and it broke. I got a straight screw extractor and got the rest of the bugger out. I checked compression on the first two cylinders, it was 145 and 150, after that my compression gauge broke (valve stem got screwed up). Only after that did I realize I did the test with the throttle closed, I was supposed to do it WOT. Problem with the plugs was there was a lot of rust flakes around the plug, but I removed them before removing the plugs though. However, I am still extremely nervous that if one got in it might seize up my engine, don't know how I will go boating once this thing is running properly:nightmare:. Anyways, after new plugs today its running even worse. While before it acted up at around 3600rpm with a load, now it does this at idle, almost dies. The new plugs did help some, but with a different kind of misfiring. The misfiring I am having now is the engine runs good and then has a big blip, almost as if someone hits the shift interrupter, its shaking like crazy, almost trying to jump off the mounts. Before it had a misfire at idle but occasionally on one or two cylinders, and the new plugs cured that, but the misfiring I am having now seems to be most if not all cylinders cutting out. Now one stupid thing I did before the day this started (first day out, so not sure that this is causing it) is I left one of the plugs disconnected, I forgot to reconnect it and went out boating. After launching the boat and starting the engine, it smoked a lot and I swear I could hear the spark wire zapping over the sound of the engine.:facepalm: The coil is brand new, maybe I put like 2 hrs on it or so, and so is the cap and rotor. The engine starts up with just a touch of the key when cold or warm, its just this stupid misfiring. Also I am hearing clatter from the valve lifter area. It gets less when the engine warms up, but after this problem got worse after replacing the plugs, the clatter got a tad louder and a bit higher up. Despite this all, I am now thinking I have a fuel issue. I will dump out the bowl on the bottom of the pump and see what its got in there, maybe run from a different fuel supply. Is it safe to disconnect the fuel line at the tank and stick it in a jerry can? I really don't want this thing to go up in flames, I just turned 18 and my 10k boat burning down is not fun!

 

[tank1949]

Get schematic and book and make sure that plugs were gapped correctly. Even new plugs get dropped or banged up. Trust me!!! Make sure plug wires went on correctly to PRECISE cylinder (yep, I have gotten them out of order too). Make sure plug wire's boot didn't separate from main wire causing crack or lost continuity (been there too). That old, the plastic/rubber of the wires may have fused to the plugs over time, and yanking on the wires to remove them may have seperated them internally. If plug/wires were 20 years old and plugs were rusted into place, there is a good possibility that you have found your main issues. Be thankful!!! You can use a vacuum cleaner to suck out old crap and rust flakes if you are concerned about rust contaminates. I use an anti-seize on new plugs. BUT, I boat in salt water. Down here, everything rusts or corrodes. Good luck! We all learn!

 

[Southtowns27]

Take a video of the engine running. The "tapping" sound is making me question if you've got some kind of internal mechanical issue going on

 

[vroom ZOOM]

ok, update. I pulled the fuel filter and the contents of the bowl, no water. Next I drained the contents of the fuel line into a glass container, also no water after sitting a few hours. I don't think ethanol is an issue because I always use premium gas (91 octane) and that stuff is guaranteed to be ethanol free (or at least they say so). Also checked the gap on the plugs and it is right on 0.035. One thing about the plugs is that one of the packages was opened before, maybe it got returned because it was messed up, i don't know. I ordered a new fuel filter and carburetor inlet screen anyways. Next while it was apart I pulled off the valve cover and busted the gasket. I don't see anything abnormal that could cause the clacking noise, all the rockers have 0 lash (yes I turned the motor to make sure none of the valves where about to open). Didn't find anything under the valve cover so I pulled off the dizzy cap. the button on the cap is springy and shiny on the tip, and the posts on the inside show no wear or soot. So now I think there is a few things that might be wrong.

1. ignition system, maybe the plug wires, I am looking for new ones right now, also could be the timing advance module? (will have to check with timing light)
2. carburetor is plugged (really doubt it, it wasn't doing this two days ago, can it get plugged in two days?????)
3. internal engine damage (will a compression test rule this one out) This one would REALLY SUCK, because I want to sell my boat right now and already one person showed up and it ran like crap...

 

[vroom ZOOM]

Edit: sorry, meant 0.045, not 0.035!

 

[Southtowns27]

A compression test may or may not reveal internal engine damage, depending on what failed. Again, post a vid of it running

 

[merc120_81]

Food for thought, and keep it simple principle... Double check you have your firing order correct / wires correct.

 

[vroom ZOOM]

1342 is what I have right now, i have double checked. Video is still uploading. It ran a LOT better after changing the gap from 0.045 to 0.035, but it still has a thunking and claking noise.

 

[vroom ZOOM]

heres the video, it is after regapping plugs to 0.035

 

[vroom ZOOM]

Is it at least safe to run with those sounds? I think one of them might be the valves, but I have to warm it up for a valve adjustment.

 

[Southtowns27]

It's hard to tell from the vid, but I think I hear a rod knock or something in the bottom end. Does it sound like someone is hitting the inside of the engine with a hammer somewhere down low on the block? What's the oil pressure after it warms up?

 

[vroom ZOOM]

oil pressure is 40 psi at idle warmed up, and it goes up very little once I rev it up. Doesn't seem like its down low, it seems to be coming right from the spark plug area.

 

[vroom ZOOM]

ok, here are the results of a compression test I just did:

#1 170
#2 160
#3 170
#4 165

so it doesn't seem like a bad piston. I did the compression test at WOT and a cold engine. Any ideas now as to what i should be looking at? I thought #3 was the problem cylinder as that was where the tapping noise seemed to be coming from, but on the contrary it is the best of all. what the heck do I do now? At least I don't think I have to replace the engine!:lol::whoo::lock1: Funny that this issue popped up all of a sudden, and right after winter storage. I will also post a picture of the spark plugs right now, they seem WAY too sooty for new plugs that ran for a couple of minutes at idle speed.