Hello All.

I just bought a 2004 Sunsation 288 over the winter with a 525efi. Speeds are down from wjhat they should be by about 5-6 + mph. Tried a few different props but feel like its propped correctly, compression is good, plugs look good but only checked them cold not after a WOT pull.
Transom is getting very black and it sounds a little rich.

Has about 210 hours on it, valve springs have not been replaced to my knowledge, but I plan to do them over the winter.

Brought it to a local dealer to scan it and it comes back with a code that the ECM thinks the motor is 32degrees which is default if there's no reading I believe so its running full rich which makes sense.
Issue is he tested the coolant temp sensor with an ohm meter and it tests fine. He can also hear the motor change rpms when he plugs it in or unplugs it so the ECM is picking it up.

Any idea what could cause the ECM to read 32 degrees coolant temp and go full rich besides the coolant temp sensor?

Also do you think running full rich would drop the rpms by about 300 or so on top end?

I will probably order a sensor and replace but I wont be able to get one right away and its kind of a ***** to get to but I really dont think thats it.

Any ideas would be appreciated!