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Joe, Marine Mechanic
Category: Boat
Satisfied Customers: 7251
Experience:  ASE, electronics, Marine mechanical and electronics, pwc, wiring, all around repair tech,
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2.4l (2004) mercury jet drive in a sugar sand Calais. Runs

Customer Question

2.4l (2004) mercury jet drive in a sugar sand Calais. Runs real rough at idle. vibrations can be felt through the deck. No problem with it cutting out, but really loud and rough at idle. Is this and ECM issue? Oil? Smooth as a sewing machine on plane. No rebuild on this engine that I can tell.
It might be loud due to the exhaust system they have in place but it is a rather unsatisfying note (sound).
Submitted: 1 year ago.
Category: Boat
Expert:  Joe replied 1 year ago.


Thank you for allowing me to assist you, my name is ***** ***** I will be happy to assist you with your concern today.

There can be various reasons for this such as:

Engine/pump not balanced

Engine motor mounts

Driveshaft bent

Poor running condition such as fuel issue, spark, compression, etc. This could be a problem with low speed jet/settings as well and need a carb rebuild unless efi which is fuel injected in which you would want to check fuel pressure and throttle position sensor as well as the iac and for other air leaks. You could have an tps reading incorrect at idle only.

Exhaust esp loose exhaust

Note that a bad motor mount can lead to/cause loose/disconnected exhaust as well.

Thank you!
- Joe

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Customer: replied 1 year ago.
Doesn't feel like a harmonic that you would get from an imbalanced shaft that would be created at a fixed RPM as that would be constant. It runs fine for 2 seconds and appears to stumble, then go 5 seconds and stuble then 3 seconds and stumble and rattle the deck when it does. I was told that this unit deactivates two cylinders but I cannot verify that. Does it? It is an EFI motor so I don't think that there would be a carb issue. Compression is sitting at 135 across six cylinders.What is an iac?Engine / impeller balance? What does that entail? I would need to see the impeller, can I do that from the bottom of the boat while it is pulled?
Customer: replied 1 year ago.
FYI, this is my first experience with a jet and it is a different bird.....
Customer: replied 1 year ago.
BTW, I believe it is a 2.5l not a 2.4l and it is labeled a 240hp.

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