Merc 5.7 loss of power and clicking

[John Evans]

Last night running around 3300 rpm up the river to pick up some friends for dinner I heard some clicking and had a sudden loss of power. I looked under the hatch and she was idling fine, I got her back up on plane and ran around 20min in and 2 30min runs to dinner and drop the friends off with out a recurrence. on the trip home however she wouldn't run very far without the clicking and power loss. Idles fine, good temp and oil pressure, it doesn't seam to miss just power down.
Merc 5.7 Bravo 3 SternDrive
Any Ideas?

 

[bigbass032]

Re: Merc 5.7 loss of power and clicking

Maybe a rocker came off, causing one cylinders to have low compression, make ticking noise, but still idle fine.

 

[Coors]

Re: Merc 5.7 loss of power and clicking

fuel/water seperator been changed?

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

Could that cause these symptoms? I'll check it tomorrow. Also this is as low as I've ever run the fuel, down to about 1/4. I'll carry 20gal or so of fuel down to the lake as well. I initially thought it was some safety rmp limiter.

 

[Don S]

Re: Merc 5.7 loss of power and clicking

If you lost a rocker arm, you would have a dead miss and it wouldn't idle "fine".
Of course I have had customers come in saying it ran fine, only to find 2 cylinders on a V8 that had ZERO compression.
So maybe a compression test should be one of your troubleshooting steps.
Might also inspect the distributor cap. A cracked cap with a little moisture and you have some serious cross fire.
Also, pull the spark plugs and look at them, do they all look the same, any thing strange about any of them?

 

[bomar76]

Re: Merc 5.7 loss of power and clicking

Maybe a rocker came off, causing one cylinders to have low compression, make ticking noise, but still idle fine.

How do you explain the rocker arm coming off, reinstalling itself and then coming off again??????

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

deleted

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

If you lost a rocker arm, you would have a dead miss and it wouldn't idle "fine".
Of course I have had customers come in saying it ran fine, only to find 2 cylinders on a V8 that had ZERO compression.
So maybe a compression test should be one of your troubleshooting steps.
Might also inspect the distributor cap. A cracked cap with a little moisture and you have some serious cross fire.
Also, pull the spark plugs and look at them, do they all look the same, any thing strange about any of them?

She starts and idles great. On the last run it got up on plane as normal, about 30 seconds in I hear a clicking / snapping sound followed by a power loss like I pulled the throttle back. After the first few times I was afraid to do anything but limp home.

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

Checked everything I could and found nothing out of the ordinary. Out of gear I eased the motor up to 3200rpm, good temp and oil pressure. Idled out a bit from the dock and floated with the wife and dogs for a while theen eased the boat up on plane to around 3400rpm, nothing odd. I was afraid to gun it and see what happens with that crew. Still looking for ideas.

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

Still having this problem. Summer?s almost over and I?ll have it looked at over the winter. Still looking for suggestions. My wife says it sounds like beer cans bouncing around down there. Idles fine, out of gear runs @ 3-3.5k rpm smooth, good oil pressure and engine temp. In gear she makes the noise and looses power around 3k. Any ideas?

 

[Don S]

Re: Merc 5.7 loss of power and clicking

Did you pull the drive and check ujoints, gimbal bearing, and drive?

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

Is the clutch assembly on the top of the out drive an overload clutch? Could this cause the symptoms? I'll soon pull the boat for the winter and have a close look.

 

[Bondo]

Re: Merc 5.7 loss of power and clicking

Ayuh,......

Did you ever Check the Fuel Filter,..??....
It sounds like it's going Lean in the upper rpms,+ That's causing Detonation........

 

[Flukinicehole]

Re: Merc 5.7 loss of power and clicking

I know this might sound stupid but how old are your ignition wires? They could be making your clicking sound but with out hearing it I don't know. My boat lost upper RPM power last weekend and ran fine at idle. I started it when I got home to flush the engine and found a bad wire. I`ve seen this more then once but like I said with out hearing it I don`t know.Start it at night and look for sparks. Move the wires around also while it`s running and look all around.

 

[akwalker]

Re: Merc 5.7 loss of power and clicking

I second the ignition wires as a possible source. Don S also reccomended cap and rotor, was it ever done? Sounds like something bouncing around causeing intermittent power loss.

 

[Don S]

Re: Merc 5.7 loss of power and clicking

Is the clutch assembly on the top of the out drive an overload clutch?

It's not an overload clutch, it's the transmission. Fwd, Neutral and Rev.

 

[whywhyzed]

Re: Merc 5.7 loss of power and clicking

when it "loses power", does the engine rpm increase or decrease.

(that's my new favourite t/s question)

 

[Robj]

Re: Merc 5.7 loss of power and clicking

The beer cans rattling sound could be pinging. Check your fuel system, filter and pump. Do a full tune-up and while doing so check your compression. See if that resolves your problem.

Have a great day,

Rob.

 

[wire2]

Re: Merc 5.7 loss of power and clicking

Ayuh,......

Did you ever Check the Fuel Filter,..??....
It sounds like it's going Lean in the upper rpms,+ That's causing Detonation........

The beer cans rattling sound could be pinging. Check your fuel system, filter and pump. Do a full tune-up and while doing so check your compression. See if that resolves your problem.

Rob.

I concur. Sounds like detonation. Poor wires don't make any noise.
Is it a Rochester Quadra-Jet carb? there's a filter at the fuel line into the carb to check also.

 

[John Evans]

Re: Merc 5.7 loss of power and clicking

At the dock it'll idle fine and I can run it up to 3200rpm or so with no odd behavior. Could any of these possibilities occur only under load or with a raised bow?