I have a 2008 280 with twin 4.3...

[Islamoradamoon]

I have a 2008 280 with twin 4.3 MPIs and alphas.  A couple of months ago, I noticed the starboard needed a little more throttle to balance the rpms on a plane.  At first it was barely noticeable but got a little worse over a period of three months.  The last time I took the boat out, the starboard engine was noticeably running rough and I pulled the plugs when I got the boat home on the trailer.

The plugs were all blackened indicating rich running.  That was until I pulled the number 2 plug (the last one I got to) and found the entire center electrode missing and much of the ground electrode burned off.  Plugs had about 40 hours on them and were the correct plugs - changed in the spring of 2016. The #2 cylinder had no compression when checked, pumped some oil in the cylinder and still had no compression.  Checked the adjacent #4 cylinder and had 155.  Pulled the valve cover to check springs/valve movement and they appeared normal. 

Took the boat to a local, well reviewed, mechanic.  After looking, diagnosed a "detonation failure" possibly as a result of #2 injector running too lean and the sparkplug burning up. Possible bent valve or piston issue.  Recommended re-manufactured engine from Jaspar which I elected to go with.

Has anyone had issues of this nature with injectors? Mechanic will service injectors when new block is installed but I would like to have some idea of exactly what would cause this.  Next time my engines are not running balanced, you can better believe I will be paying a lot more attention to the issue than I did this time!

[Offline]

Same thing happened to my 2006 280. Needed new engine. The blame was a faulty plug.

[Islamoradamoon]

Offline, did you experience any more issues with that engine? The mechanic is thinking possible injector problem because plug failure is rare...

[Stubie]

I have a 2001 310 with dual 5.7's - my port was rebuilt before I purchased the boat a year ago; the starboard runs at 4,500 rpm and the port will not get over 3,000. I've spent thousands to ID the issue and factory authorized mechanics cannot figure it out. One Mechanic injectors on the port engine rebuilt; 3 sets of spark plugs, re-flashed the ECM's, new map sensors and fuel additive....the list goes on..........so frustrating! Still no solution, anyone have any ideas?

[Brite_Idea]

When the ECM is failing it be hard to diagnose while causing lots of damage. Fuel injection is great until it has issues. I had an ECM go bad slowly over two season and many trips to the mechanic that finally fixed it. During that time time we went thru 10 sets of spark plugs and lots of fuel. The worst part was when they finally diagnosed that the ECM was bad Mercruiser no longer made them. Mercruiser offered a 4000 dollar upgrade kit! I ended up finding a new ECM on the shelf in California. The loss of an engine due to injector failure or some other electrical failure sucks! I wonder if we were better off with carburetors?

[Offline]

I did not Experience any more issues with that engine

[Creola]

I had a 2005 280 that experienced same problem. It was a non-firing plug NOT due to the plug but due to a tie wrap that was too tight on the plug wire against a metal ring on the engine. The plug wire insulation got a break in it and was arching onto the metal ring versus making it to the cylinder. Replaced wire and problem subsided. I had a 2008 330 Sundancer, big block 496's. The 496's are designed to equalize power if a cylinder quits and these engines are beefier than the 4.7's, so I didn't notice it at first but I did notice a less ramp up on starboard engine vs port when coming up to plane with a heavy passenger load. I immediately checked wire tie wraps and found the same thing. Evidently wires are tightly wound and tied at factory and with a little wear and/or some rough water can, on some occasions, pinch wire insulation enough that a little pull or friction can cut the insulation. If they're near something metal, they can short them out. I just bought a new '17 350 sundancer and the first thing I did was get in the engine hatch and look at all wire bundles and tie wraps. I did find one that seemed incredibly tightly tie-wrapped against a block ring. This thing had 3 tie wraps and the wires were crimped like guitar strings!. It looked neat and secure but it got my attention. I called my tech rep and asked about cutting off tie wraps and re-wrapping...but with less torque. (Enough to be secure but not stretched tight like a rubber band.) He couldn't "endorse" this per se but knows that I know my way around an engine hatch and related it probably couldn't hurt. So far so good. I'm not negating the possible injection issues you relate. But the initial root cause of a plug not firing seems to also be a common thread here.

[Islamoradamoon]

Good information Bank of Bad Habits (from a fellow JB fan). The plug wires have been changed multiple times since I bought the boat, last year I changed them myself. The original factory wire ties must have been cut off when I had the dealer change the wires 4 or 5 years ago since there were none on them when I replaced them last year. Had the plug not been firing, I would not have ruined the cylinder I suspect. I have had plug wires come off and noticed the miss but this failure actually had the spark plug come apart and either damage a valve or the piston.

[Islamoradamoon]

The mechanic I ended up taking the boat to, Boaters Edge in Titusville, FL, found the issue very quickly. The plug was not the root cause, fouled injectors were. The #2 cylinder injector leaned out the mixture to the point that the plug burned up and the cylinder wall was scored. All the injectors on both engines were cleaned when a remanufactured engine from Jasper Engines was installed. I have never heard of injectors doing this but it seems to be an issue that everyone running ethanol gas needs to remain vigilant about. I know I will in the future...