1998 200 HP EFI Mercury not getting up to speed.

[JoseyW]

So I have a 200HP EFI motor on my boat. Last weekend I was driving across the lake at about 40mph which is about max for my boat. All of the sudden it was like I was loosing gas to the motor. It started sputtering like it was going to shut off but never did. I drove it to my camp loaded all of my gear on the boat (I never shut the boat off) and drove it back to my truck I was only able to get it up to 8 mph. Which on the was out with all of the gear I was going about 35. Brought it home and tested the ignition system to start it seem that the stator the boxes and coils are all good. Looking to see what else it could be. It seemed that the exhaust was spitting out some oily looking substance in the water, normal for a 2 stroke? Boat starts fine in the driveway.

 

[Faztbullet]

Start with a compression test first, then check the fuel pressures and diaphran in mechanical pump.

 

[JoseyW]

K I’ll check that tonight. Do you know what the compression spec is? And the fuel pressure spec?

 

[JoseyW]

Well one of my cylinders has 0 psi, another at 60, and the rest at 90-105. Think the problem is found

 

[Faztbullet]

yep pull the head and inspect.....

 

[QBhoy]

Oh no...so sorry. Horrible thing. Happened to me with an early 90’s 200 Merc. Was the oil injection system failed. Perhaps likely you had the same problem. Well known for it in the big v6’s of a certain age. Perhaps yours was an improved version though ?

 

[JoseyW]

After a complete tear down of the motor I had 2 pistons fail. They scored the side of the piston walls so bad that they need to be re-sleeved to fix this block. Not sure the initial cause of the piston failures yet. It seem the oil injection was working fine. I do have a question on as if anyone knows of a place to find sleeves for this motor block or where to find a new/used block. I’ve been told mercury isn’t selling the blocks anymore.