350 MPI running very rough, will not idle, loud tap

[mjfink]

Went down to take the boat out today and, after dropping it back in the water, the engine really didn't want to turn over (sounded like a dead battery). I switched to the other battery, and it turned over slowly and then started hard. Would not idle, but would run with the throttle advanced to about 1000 RPMs or so. Loud tapping sound out of one side of the engine. No overheat or anything like that (but only ran it for a min or so). Water was flowing through the engine correctly (I could see it on my flush system check valve).

Last time I ran the boat, it was fine; ran it off a hose a few weeks ago and everything sounded great.

I checked the oil and it looked high to me, but that could just be my imagination.

My guess is that I somehow, when running it on the hose, forced water into the engine and partially hydrolocked it. Please don't let this guess prevent anyone from making suggestions though!

The tapping sound was related to RPMs. Seemed to be mostly on one side of the engines. The manifolds are good (recently checked).

Engine is a 2006 350 MPI, Serial Number OW370643 (If that helps).

Thanks for any help!

 

[Don S]

Re: 350 MPI running very rough, will not idle, loud tap

after dropping it back in the water, the engine really didn't want to turn over (sounded like a dead battery).

When you say it didn't want to turn over, did it start to turn and stop? Did the starter click or was there a loud clunk when you turn the key?
It sounds like you may have hydrolocked the engine (water in a cylinder) and you eventually pushed the water out when using both batteries. May have damaged something.
Pull all the spark plugs and do a compression test and see what you get.

 

[mjfink]

Re: 350 MPI running very rough, will not idle, loud tap

It did start to turn and then stop. No click that I could hear, it sounded like the engine trying to start on a dead battery.

That's what I'm afraid of (hydrolock). I'm assuming this must have happened when I was flushing the engine (as it was the last time the boat had water running through the block). I'm always very quick to shut off the water after I shut off the engine, I guess I wasn't fast enough this time.

Why do you think I have the rough idle now? The tapping I'd associate with some sort of internal engine damage or issue, but the rough idle? Think I'm "missing" a cylinder or 2 and it's causing it to idle badly?

<sigh> Trying to be careful with the engine (by flushing it) and wind up with a hydrolock.

If you had to guess, what do you think I damaged that's causing the ticking? Valves/lifters? Or something deeper (crank or rod?)?

 

[Don S]

Re: 350 MPI running very rough, will not idle, loud tap

Flushing shouldn't cause a hydro lock, I would think you had a better chance backing it into the water. Next time you flush it, shut off the water and crank the engine over and see if you have a problem. Also, test crank it before you leave for the lake. If ok then and you have problems in the water, you will know where the problem started.

 

[joewithaboat]

Re: 350 MPI running very rough, will not idle, loud tap

Hard to say, one mans tick is another mans knock.

Post a video or like Don said run a compression test. Then post the numbers.

Good luck!

 

[mjfink]

Re: 350 MPI running very rough, will not idle, loud tap

Huh.. Interesting, I'm thinking that's what I'm dealing with (hydrolock) because of all the initial symptoms (hard to turn over and start initially).

The boat hasn't even been in the water since it was running well; the last time I ran it, it was only on a lift (well, the engine was in the water, but the boat never moved/no waves/etc, so no way for it to injest water that way)..

I didn't start the boat on the lift today, I dropped it into the water and then started it, but, again, it wasn't even totally submerged, the leg was the only thing actually all the way in the water (I always start on the lift in case, like today, there's some immediate issue that would make it hard to get back up on the dock).

I'll report back after the mechanic comes out to take a look at it. Hopefully I'll be here when he comes and I'll get some video of the sound/symptom for everyone and then the solution (or cause).

Thanks for the help, I appreciate it, and any more ideas/suggestions, please feel free to keep'em coming.

Flushing shouldn't cause a hydro lock, I would think you had a better chance backing it into the water. Next time you flush it, shut off the water and crank the engine over and see if you have a problem. Also, test crank it before you leave for the lake. If ok then and you have problems in the water, you will know where the problem started.

 

[mjfink]

Re: 350 MPI running very rough, will not idle, loud tap

"Hard to say, one mans tick is another mans knock. "

Good point. If I had to say, I'd put this closer to "knock". It's a rather loud banging noise, not like a "ping" from bad/old gas or anything like that. It's also totally dependent on engine RPMs. Interesting, it seems like there's a range (around 1.2K RPMs) where it stops. Above that, it comes back, and below that, it's also there (but at a slower frequency).

 

[mjfink]

Re: 350 MPI running very rough, will not idle, loud tap

Mystery solved.

Water in 5&7. Knocked the lifters out of position and was causing a knock.

Compression is low on these 2 cylinders (110lbs or so), but my mechanic thinks that it's because the valves aren't seating correctly and suggested sending the heads to a machine shop. He's pretty confident that the bottom end is OK. This sound normal (IE, like it's the right course of action to take)? Also, of course, we need to figure out where the water came from and fix that as well, but, does this sound like the right course of action for the engine damage caused by the water entering?

Thanks!

 

[mjfink]

Re: 350 MPI running very rough, will not idle, loud tap

Also, interestingly..

The mechanic was surprised to find water in the intake manifold. He guessed it was probably from the water that was in the cylinder, it pushed into the intake manifold when the valves let go. Seems logical, I just wondered if anyone had ever seen that before.