5.0 MPI Bravo 3 won't do full acceleration, need suggestions

[Mouseketeer53]

I have a 2005 Searay 240 Sundeck with a 5.0 MPI Bravo 3 I/O engine. It has a Cool fuel box. It had been running fine and at full acceleration would top out at approximately 48 to 50 MPH. Suddenly during use it slowed down and now tops out at about 32 MPH. It will not go above that. I have performed the following maintenance:

Cleaned throttle body and filter.
Replaced fuel filter in the cool fuel box.
Checked fuel pressure at idle and full throttle. Fuel pressure is between 40 and 50 pounds in both instances measured at the Schrader valve.
Checked throttle linkage from cockpit to throttle body.
Took out old fuel and put in new.
Now going to pull a spark plug to check carbon buildup.
Any other suggestions? It seems as though it is starving for something.

 

[muc]

Cylinder balance test would be my next step.

Sounds like you have lost power on one of the cylinders.

 

[harleyman1975]

I agree sounds like a plug wire fell off or perhaps a plug is broken or perhaps an injector failed or has come unplugged also I would do a compression test if none of the easy things fix the problem.

 

[alldodge]

I would suggest checking for codes, but would help to know what your serial number is

 

[Mischief Managed]

Check your cap and rotor for carbon traces. I'm pretty sure that engine has the crab-style flat-top cap and they are susceptible to that.

 

[QBhoy]

As mentioned, distributor cap and rotor removal and clean might help. Known problem on these engines. Just recently found this out. Apparently a service manual revision about it. My symptoms were not starting and miss fire when releasing ignition key, after winter storage. Heard of it also happening mid season too (from forums)

 

[Mouseketeer53]

As a follow up, yes it was a plug wire. One of the wires was up against a hot area and melted. Discovered it when we decided to replace all the plug wires. Thanks to everyone who suspected this was the issue. We have now been up to full speed.....until a recent problem with no fuel pressure. I have posted this under a new topic. Frustrated beyond belief. Have put in a new cool fuel module, sea water pump and several other items. Still no luck.