1993 OMC 5.8 EFI won’t reach max rpm

[BenChamberlain]

Model - 58FAPRJVB

TFI-V ignition system

i have a Chris craft concept 237 with the omc ford 351 EFI recently I was testing propellers to find my ideal WOT rpm 4200-4600 as per manual. The boat came with a 15x15 prop and I could tell emmidiately it was under proped so I borrowed a 14.5x19p last season to get me through but still just outside the ideal range. The other day I started the boat and went for a cruise the with a 14.5x 21p and the rpms seemed to have dropped way too much by about 1200.. from just under 5000 at wot to 3800-3900 so I went back to my 19p same rpm at wot for jokes I threw the 15p prop back on barely cracked 4000rpm at wot. I looked over all hoses and around the injectors nothing seems to be leaking all the wires from the coil to the cap and plugs seem good I pulled a couple plugs they seemed fine too. Does any one have any suggestions where to head next?

 

[alldodge]

Not reaching WOT can be many things, the problem is finding out which one(s) it is.

Start with the basics, check compression, timing, fuel pressure and also check spark on each plug with a spark gap tester. If your loosing spark on one or more plugs, the boat may sound fine running at higher rpms, but its not getting a good burn

 

[PGATOO]

burnt out or broken exhaust flaps sometimes will create the same symptom