5.0 mercruiser w/ 40hrs running rough

[NVR DED]

I was running across the water today after it has been running flawlesslyfflawlessly the last two months since I bought it. It lost power and shutdown. This motor was replaced in 2017 and when I bought it, it only had 15 hours on it. I had a solid beep like the ignition key was on right before I start it. I turned it off and it didn't want to turn over at first. It acted like a weak battery. I gave it a minute or two and then it started turning over like normal but once it fired it started running really rough. Earlier in the day I noticed the oil pressure was a little high but it returned to normal 40psi pretty soon after. I'm not really sure where to start diagnosing. I'm fairly savvy with car/truck motors and outboards but not these. First one I've owned. It was suggested to me that the oil pressure switch may have failed but would that cause it to run rough? I've heard of "limp" mode kicking in when the computer detects some sort of failure. It didn't get hot but boy it sounds bad whereas it use to run whisper quiet and smooth.

Where to start?

 

[achris]

Hi NVR DED and :welcome:

What you describe sounds very much like a few cylinders getting wet, probably from a manifold leak. As this can cause problems if left unattended to, I would recommend you look into it IMMEDIATELY. If there is water in the cylinders, it's there right now, doing it's best to spend your money, RIGHT NOW, as you read this post!

So, pull the spark plugs out and look at them. See water, problem. Spin the engine over on the starter to clear the water, then pour a few ml of 2 stroke outboard oil into each cylinder, and with the plugs back in, but disconnected, spin it over to get the oil into the rings. Hopefully you will have preserved the engine.

You need to pull the manifolds and set up to pressure test them, or get them pressure tested.

One more thing. No such thing as 'limp' mode. It's called Guardian, and it will limit the available power and revs based on what fault has been detected. Is your engine MPI or carburetor? (no Guardian on carbs). We actually like to see engine serial numbers posted. We can use those to look up what engine you have without have to constantly be saying, make, model, year and serial number.

Chris.........

 

[NVR DED]

Dang. Ok. I'll go out there and pull the plugs right away. And look for the serial number as well. Thanks for the quick reply and the welcome.

 

[NVR DED]

Ok I pulled all the plugs and bumped the motor on every other one. All of them were dry. One looked a little foul but nothing too bad. Where is the serial number on this thing?

 

[NVR DED]

Also my ignition switch in the dash has been acting funny like it has a loose connection. Think that could be the issue? Possible that the vibration of the boat has finally pulled it loose enough to cause an ignition issue?

 

[NVR DED]

Cleaned up the ignition wires in the dash. Fires up nice and quick but still runs rough with a lot of vibration. I started polling around on the lower unit while I wait for some more help on getting the motor right and I ended up taking the lower unit off. In behind the prop I found a chewed up piece of rubber, some kind of gasket that didn't seem to come from anywhere. It was just sitting down there? Very odd. Also when I dropped the lower unit there seemed to be some significant metal shavings around the drive shaft. More than just some glitter a few decent sized chunks actually. Transmission issues? Ugh I'm lost obviously.

 

[Rick Stephens]

A couple things to think about.

When you say pulled the lower unit - you mean just the bottom half of the drive? Why not the entire drive? That's an annual maintenance thing anyway and very easy to do.

You found some rubber pieces - take a picture and post it. Have to resize the photo to get it accepted on the forum. Could be parts of your exhaust shutters, some pieces of the impeller, or something else?

Metal shavings - again - from the shaft into the lower gear case or at the splined end of the driveshaft going into the upper gearcase?

 

[NVR DED]

I only pulled the lower half. Just trying to make sure the impeller was in good shape while I try to figure out my other issue with the motor. I will end up pulling the whole thing after the season but again just trying to get it ready to go again ASAP. Impeller looked to be fine and there was zero water in the drive lube so the seals were good. The rubber piece was a big gasket of some sort. I'll take a pic and try to post it. It doesn't look like it belonged anywhere near where it was. It was in the hub behind the prop. Very odd place for something that big it seems.

The metal shavings were on the drive shaft going up into the upper gear case.

 

[NVR DED]

Pulled all plugs again and confirmed they all have spark. Still running rough.

 

[achris]

With the engine running, pull each plug lead off in turn. Make sure all cylinders are firing.

Serial number will be on a tag down near the start motor...

Chris...

 

[Rick Stephens]

If you have metal on your shaft splines coming from the upper, better pull off the top cap and look at the gears. Sounds like something is eating itself.

 

[NVR DED]

It doesn't sound like they are all firing but each plug is definitely firing. I feel like I need to do a compression test on each one now. I have the lower unit off so I can't circulate water. Wouldn't checking the spark basically be the same thing as what you're saying Chris? I pulled the plugs one at time, reconnect to wire and ground the plug on the motor. I see spark each time I do that.

I agree Rick, it doesn't look good with all that metal on the upper shaft. Is there a cover on top of out drive that let's me see inside the upper gear box? I have a swim deck so that may need to come off to get a good look.

 

[Rick Stephens]

The top of the drive has 4 3/8ths 12 point bolts. It pops off pretty easy and the gears are right under it. Don’t need a lot of room.

 

[NVR DED]

Well I don't know how to see the serial number without being a contortionist. Starter motor is completely obscured by the exhaust manifold. Can barely touch it let alone see it.

But the boat is a 2002. However supposedly the shop put in a new motor in 2017. Perhaps a rebuild? Doesn't look new to me. I confirmed they did with receipts.

 

[NVR DED]

Well I think I found the problem. The gear that is under the plate on top of the Outdrive is missing two teeth. It chewed up the housing a little bit. Rick Stephens achris I'm going to load a pic of the damage. Can this be repaired? Or do I have to but a new one?

 

[NVR DED]

[No message]

 

[nola mike]

Nope, that's toast. You'll need a new complete outdrive, that metal is everywhere in your drive now. What did the gear oil look like when you drained it? The good news is that although the fix isn't cheap (unless you find a CL special), it's easy...
It will cost more to fix than buy a new one.

 

[Rick Stephens]

Just get an SEI drive and swap in. Go boating with a 3 year warranty.

 

[NVR DED]

Gear oil looked normal. Besides the metal chunks of course.

SEI huh? Ok. I'll take a look. I thought the same thing. That would be more to repair than to replace. Do shops the sell them offer any core charge for my old one?

 

[NVR DED]

How does something like this happen? I didn't hit anything... Was just running across the water at 80% and the motor lost power as I described originally. Then it was hard to start. Assuming the gears were locked up. I hit my battery switch and combined my batteries and it turned over. I'm guessing that's when the gears sheared.