2005 Mercruiser 3.0 Liter losing power and rattling high RPM

[Birchbark18]

Hey guys,

Just took my 05 Sea Ray out yesterday and I'm having an interesting issue - about 4000 RPM a rattling noise starts and continues up to WOT. After about 10-20seconds I start losing power, but the engine doesn't die and if the throttle is pulled back to 3000 RPM the sound goes away and engine runs normally. No issues at idle, or any other power range.

Compression test was 150, 120,120, 120 in the cylinders, and one plug has some moisture (fuel/oil) the others were dry. It seems like compression is in range so I'm thinking fuel delivery issue? But that doesn't solve the rattling. Any help would be much appreciated.

 

[Rick Stephens]

Scary part about calling high RPM problem 'rattling' is that could very well be pre-ignition pinging which will eat a motor. Pistons will disintegrate and valves will melt. All caused by running too lean.

What did the plugs actually look like?
What does the fuel look like if you pull the fuel water separator and dump its contents into a clear jar?

 

[Birchbark18]

So here's the plugs.. I'll check on the fuel water separator this afternoon. Again not overheating at all if that would relate to it running too lean. Also can't tell yet if the sound is coming from the engine or the outdrive, but regardless it causes a loss of power shortly after.

 

[Rick Stephens]

That third one looks like the tip is pure white. I'd say lean.

You will not see temps go up - you are running with unlimited cooling. It'll just eat the pistons away.

Dump and look at separator contents. I'd personally just assume I also need to rebuild the carb. Don't reuse the filters.

 

[Birchbark18]

So this afternoon it was subsided until the engine warmed up, then same thing 3500 to 4000 RPM, loss of power and actually noticed temp go from 150 to 180 as the power throttled back.. is that an engine mechanism to prevent damage? Could this be an impeller issue at all?

 

[Birchbark18]

I'll also be looking at fuel tomorrow morning including filters

 

[Bondo]

Ayuh,..... Welcome Aboard,...... I concur with Rick,.... Sounds like it's goin' lean, causin' detonation,.....

 

[Birchbark18]

Thanks guys, appreciate the help. I pulled the filter this morning and it definitely was deteriorating. I'll replace it and try that. Should I be looking at a carburetor rebuild/fuel pump too because of what I've found so far or test out with just the filter replaced? I've also read about adding an in-line separator - any thoughts on this?

Also put new plugs in yesterday and pulled them to see what they looked like - 3 out of 4 were white, last one actually had some damage - see the picture.

 

[Rick Stephens]

Rebuild you carburetor.

 

[Bondo]

I've also read about adding an in-line separator - any thoughts on this?

Ayuh,..... The canister type filter is a great addition to any boat motor,......

You'll never need to change the little one again,....

In yer last picture, it looks like bits of piston stuck to the ground strap of that spark plug,......
Detonation is goin' on, in a bad way,.....

 

[Birchbark18]

Interestingly enough that's the cylinder with the highest compression numbers.. 150. Should I be pulling the head to check this out or just address the fuel issue? Don't want to score the cylinder or mess up the rings with debris while I'm figuring this out.

 

[Bondo]

or just address the fuel issue?

Ayuh,...... I'd find the Why, 1st,.....

 

[Birchbark18]

So I just finished the carb rebuild and got out to test it yesterday... at first I though the issue was fixed, but had a little hesitation to get up to WOT from idle, noise was gone. After engine got up to operating temp the noise came back. Didn't run it at high RPM again, don't want to do more damage.

For the carburetor, I adjusted the float level to 14mm from 10mm and drop accordingly because the specs said that's what was needed with the spring-loaded needle, which I had when I rebuilt and replaced with the same type. Whoever did it before did not adjust for the spring loaded needle and left the float at 10mm. Is my adjustment causing the hesitation?

My next thoughts if the carb is adjusted correctly are the fuel pump and timing. Appreciate all the help from everyone.

 

[Rick Stephens]

Well, at least timing and fuel pump are easy to check. Set the timing. If you use and electronic advance timing light you can check that the advance is working correctly.

Use a vacuum/pressure gauge to check fuel pressure. Should stay at 6 or 7 PSI all the time.

 

[Birchbark18]

Been a while, worked on the issues above and here's where I'm at:

Replaced the fuel pump - old one had some corrosion above the top bladder but not a lot, however the breather tube that goes to the carb had a lot of crap in it so it could have been going.. replaced the tube as well.

Set the timing: this to me seems like it was the primary issue. It was 10 degrees or more off, firing early at idle. I set the base timing to 2 degrees ATDC according to the manual, but when I reconnected the shift interrupter as specified the engine didn't seem to come out of base timing mode. After revving the engine slightly it would come back to a normal idle. At this point the timing advanced to 8 to 10 degrees BTDC, but the manual says it should be 15 degrees BTDC plus or minus 2. I tested the boat on the water, at WOT noise is gone and it runs well, but it does not accelerate without a slight bogging down feeling (my guess is because timing isn't advanced enough?)

My next step is ignition module - am I looking in the right spot? Looks like I can find one for around $100-150, unless anybody here knows a GM part I can swap out instead.

Thoughts? Am I on the right track here?

Thanks!

 

[Birchbark18]

Just want to give an update for anybody on here with the same problem. Got the NAPA module for around $80, plugged it in and readjusted the timing per the manufacturer's specs. Getting around 12-13 degrees BTDC at idle, and 22ish at 2800 RPM for a total advance of 15 degrees at idle and 24 at 2800. It runs almost perfect now, with just a slight hesitation when accelerating hard, and no noises. Might tweak initial timing a degree or so... but overall problem solved!

 

[Rick Stephens]

Thanks for posting back.