Advice? - 5.0MPI/Bravo III Vibration

Thanks for the tip! I'm going to see if I can see anything tomorrow or on the weekend. Who knows when the rep will show up. Once he does, I'm going to make sure that one of the mechanics that worked on the boat does whatever needs to be done gratis. I've spent too much $$ and time on this one. I could've done all the work myself and gotten the same result.

Eddie
 
What part of the wiring were you wiggling? Also, what do you mean "the data appeared" when you wiggled the wires while hooked to the computer?
 
There are two wiring harnesses connected to the ECM 555 (engine computer). The mechanic wiggle both of them and then the data in the window of the diagnostic software, which was running on his laptop, appeared. Before that point, we couldn't see half of the parameters that the software monitors. So, now I'm just waiting for the Mercruiser rep to show up and diagnose which wire(s)/connections are bad. I might look into the harness myself to see what I can find, but I don't want to completely kill my engine. So, I don't think I'll do anything major.

Eddie
 
Water U Lookin' At said:
There are two wiring harnesses connected to the ECM 555 (engine computer). The mechanic wiggle both of them and then the data in the window of the diagnostic software, which was running on his laptop, appeared. Before that point, we couldn't see half of the parameters that the software monitors. So, now I'm just waiting for the Mercruiser rep to show up and diagnose which wire(s)/connections are bad. I might look into the harness myself to see what I can find, but I don't want to completely kill my engine. So, I don't think I'll do anything major.

Eddie
Click to expand...

It sounds like if it's the ECM harness, the fix should be relatively straight forward.

Doug
 
The fix might be easy (new wiring harness), but which harness is it, and at $640+ per harness, after spending over $1500 chasing it down, I'd rather have Mercruiser find the exact wires that are causing the problem and fix it for free. If Mercruiser doesn't fix it for free, then the Sea Ray dealer that originally did the work will.

Eddie
 
The mercruiser rep came to see my boat yesterday and determined that I had a bad cylinder in BOTH engines, not just the port engine that I was complaining about. He heard it as they were starting up. So, my mechanic did a compression test and sure enough, there was 0 compression in the #4 cylinder.

Next step is taking the valve cover off to see if a valve is out of adjustment or see if the heads will have to come off and be sent to a machine shop to have the valves reseated.

VERY IMPORTANT LESSON: First thing to check when troubleshooting vibes in an rough/rich running engine is the compression. All the other stuff is easier and less time comsuming to perform once you get past the big ticket items. Also, anytime you have your spark plugs changed, you should do a compression check on the engine. It takes a few minutes and could tell you a lot about your engines.

Hope this thread helped anyone else. I'm looking to get underway next week sometime or next weekend.

Eddie
 
Lately I have heard of a ton of engines that have lost compression all due to head/valve related problems. What goes?

Doug
 
Wow...until this thread I thought the 5.0's were almost bullet proof as far as the core engine components. I've had engines with a zero compression cylinder in the past. It was never a slight vibration, and it was never as simple as reseating the valves.. Good luck and let us know what they see when they take the the covers/head off.
 
I am still chasing the problem in mine. I checked compression early on and it was fine.
 
That's a good thing. Although if you're engines are ok, then you have to check the engine coupler, or the drives themselves have to be torn down to see if anything is amiss in them. I will say that the bravo 3 drives are pretty tough based on my experience. I hit a rock and a log one season and the props were the only thing affected. Everything else was fine. I wish that were the case this time.

I'm just glad that I finally found what was wrong, even though it'll cost me for 2 new heads (one on each engine - at least that's all I hope it is. We'll see what happens when they take the heads off - hopefully nothing is wrong with the rings on the pistons in the bad cylinders).

Have a good weekend! At least you have a boat that you can run, even with a little vibration.

Eddie
 
I'll be working on the boat this weekend. The drive is off, so the problem is in the engine or transom assembly.
 
Well, they got one of the heads off and said I have a stretched intake valve on one of the bad cylinders. I've never heard that term before. Anyone know what that means?

They can only do one head at a time. So, we'll see what the other bad cylinder valves look like.

They hope to have me running this week. As long as the new heads arrive today, I don't see why that should be a problem.

Eddie
 
Water U Lookin' At said:
Well, they got one of the heads off and said I have a stretched intake valve on one of the bad cylinders. I've never heard that term before. Anyone know what that means?

They can only do one head at a time. So, we'll see what the other bad cylinder valves look like.

They hope to have me running this week. As long as the new heads arrive today, I don't see why that should be a problem.

Eddie
Click to expand...

Sounds to me like a 'stretched valve' would be the same thing as a tuliped valve. Ask for some clarification.

Doug
 
It turns out that the stretched valve is a result of the cylinder getting excessively hot. This causes the valve to get hot and allow a stretching of the stem to occur, as well as turning the bottom of the valve into a concave shape and deforming the valve seat (therefore, it never completely closes = 0 psi compression).

One cause of this overheating is from cross fire between a pair of cylinders. I remember seeing my spark plug wires laying on top of each other as well as the ignition coil, while I was troubleshooting this issue in the fall. The plastic bracket, that is supposed to separate the wires, had moved down below the valve cover, thereby becoming useless. When I had my wires replaced the mechanic did a great job of using that bracket to separate the wires and keep them from touching the ignition coil. I think my cross fire had occurred for a while and did its damage. Now at least the wires will not cause this to happen again. I would say, in general, keep spark plug wires from touching each other and check them once a year for any damage.

Soooo, it appears that I might have found the root cause of this stretched intake valve issue, and hope to stay trouble free for a little while.

Thanks to everyone who responded to the thread, and I hope this helps some other boaters in preventing similar failures.

Eddie
 
Water U Lookin' At said:
It turns out that the stretched valve is a result of the cylinder getting excessively hot. This causes the valve to get hot and allow a stretching of the stem to occur, as well as turning the bottom of the valve into a concave shape and deforming the valve seat (therefore, it never completely closes = 0 psi compression).

One cause of this overheating is from cross fire between a pair of cylinders. I remember seeing my spark plug wires laying on top of each other as well as the ignition coil, while I was troubleshooting this issue in the fall. The plastic bracket, that is supposed to separate the wires, had moved down below the valve cover, thereby becoming useless. When I had my wires replaced the mechanic did a great job of using that bracket to separate the wires and keep them from touching the ignition coil. I think my cross fire had occurred for a while and did its damage. Now at least the wires will not cause this to happen again. I would say, in general, keep spark plug wires from touching each other and check them once a year for any damage.

Soooo, it appears that I might have found the root cause of this stretched intake valve issue, and hope to stay trouble free for a little while.

Thanks to everyone who responded to the thread, and I hope this helps some other boaters in preventing similar failures.

Eddie
Click to expand...

What exactly do you mean by 'cross fire'?

Doug
 
I meant cross fire between spark plugs for different cylinders. I'm not an expert on this, but if the wire insulation is worn and the wires touch, one of the plugs could get too much ignition from the distributor and cause the temperature of the firing in that cylinder to be hotter than normal. Over time that cylinder could get very, very hot and therefore heat up a valve to a degree that could weaken the valve material, allowing it to be stretched. At least, that is my understanding of the condition. If anyone can explain it better, please do so.

Eddie
 
Water U Lookin' At said:
I meant cross fire between spark plugs for different cylinders. I'm not an expert on this, but if the wire insulation is worn and the wires touch, one of the plugs could get too much ignition from the distributor and cause the temperature of the firing in that cylinder to be hotter than normal. Over time that cylinder could get very, very hot and therefore heat up a valve to a degree that could weaken the valve material, allowing it to be stretched. At least, that is my understanding of the condition. If anyone can explain it better, please do so.

Eddie
Click to expand...

If that's what the mechanic told you, I have to call BS on that one. Many engines today have batch fired ignitions meaning that they all spark at the same time. They do this in order to burn any residual air/fuel mixture which in turn leads to a more complete combustion.

If the insulation was worn on two adjacent plugs wires, more than likely the spark would be grounding itself out on the block somewhere. Even if spark from say #2 cylinder went to #3 cylinder, this would not create a 'hotter' spark. The spark would have more volts/power behind it, but the spark temperature itself would not change.

Doug
 
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