Problems with our port engine.

[christo15]

Haven't been on the forum for a while with a crazy busy schedule. Now that the boat is winterized I have a few issues to discuss...

-Our port engine has been weak since day one. When at low speeds (close to idle) I hear a clicking/grinding noise that is very unpleasant. We already replaced the IAC (idle air control) this year but we still get an occasional stall-out. Our mechanic is having trouble determining the source of the problem. He suggested faulty/aftermarket manifolds?

-This is our most recent issue. With twin 350 mags this boat is no speed demon but we've successfully topped out at 33 mph with a light chop. Towards the end of the season, even after all the filters were cleaned/ replaced, the boat barely tops out at 16 mph with two people and a full gas tank. This is concerning and we honestly just didn't have the time to look into it before the end of the season.

I would really appreciate any and all feedback!

 

[northern]

Sounds like you need a real mechanic to look at things.
If you have over 800 hours on the engines and have run them hard it is possible you need engine work.
We got 1300 hours on twin V6 but they were getting tired compression had drop 20 PSI in 700 hours. It was time to repower or sell. We moved up to this boat and sold the other.

 

[islandhopper00]

Need way more info to even try to help!

 

[Do Over]

is it having problems pulling RPM's?

 

[christo15]

Okay. Our engines have just under 300 hours and won't pull over 3000 RPMS. I'm new to the inboard engine crowd so I apologize with the lack of information.

 

[Do Over]

Okay. Our engines have just under 300 hours and won't pull over 3000 RPMS. I'm new to the inboard engine crowd so I apologize with the lack of information.

Start with changing the plugs

 

[christo15]

Replaced them a month ago!

 

[AllTideUp]

Did you check Cap N Rotor? Wires? When was last time the air filter was changed?

 

[Quint4]

Start with full tune ups to include caps, wires, & ignition sensors. A compression check of both engines would also be good.

Get down in the engine room with the engines running and try to locate the source of the grinding noise. (water pump bearing?) Lots of stuff that will bite you down there, like belts and pulleys, so be mindful of loose clothing etc.

I had a sluggish port engine for most of last year. I spent a long time troubleshooting it. I finally found a nearly clogged fuel filter. This is a very small bowl shaped filter located in the fuel pressure regulator. Not saying this is your problem, but just one of many possibilities.

Tuneups are in order anyway (not in the category of "throwing parts at it") and it's always good to document baseline compression on both of your engines.

 

[christo15]

We had a total tune-up, replaced the cap n rotors and wires, although not sure on the status of the air filter.

 

[christo15]

Okay. I'll try to get a compression test done. The grinding noise sounds almost exactly like shifting a manual car when it's in park with the clutch in, and that's with the engine hatch closed. I'm not sure how I would get down into the engine room to troubleshoot it because it only occurs when the boat is in gear.

 

[Chris Nowell]

Could the clicking grinding noise be making the knock sensor tell the ecm to retard the timing? Could be a lot of things too though, that's why an experienced marine mechanic with a genuine interest in the industry and technology is worth his weight in gold.
1. Is your tech a qualified Mercruiser tech?
2. Has he been in the business for long enough to have been around when your engine/drive package was new?
3. Does he have access to all the dealer service bulletins for your engine?
4. Have you done wet/dry compression test, leak down test, and vacuum tests?
5. Have you performed a water test with a diagnostic computer hooked up to the engine to measure things like fuel flow, timing advance, injector performance etc? (we use a dyno for this but there aren't too many boat dealers who have one in our area)
6. Are the flame arrestors clogged?
7. Are your props the right size?
8. Do you shafts turn freely?
9. Have you measured the running temps of the exhaust system while under way?
10. Are the batteries putting out enough voltage while underway?
11. Are all wire connections clean and tight?
12. Is the fuel pressure at spec and constant?

I'm sure someone with some hands on experience with your particular set up will chime in sooner or later. Sometimes takes a few days. I wish you all the best with the diagnosis.