PCM lower unit gears

[shesha]

Hi, do you have to send your pcm to the shop if you chang the lower unit gears ratio from 1.75 to 1.62 ? Or not. I have changed the gears on my boat but the engine will not push above 4000 rpm!!! So i was thinking thats it might need to reset it up or something.

[Revolution141]

No. But it will mean the prop you ran before will be to large now, hence lower rpm.
What motor, current prop, boat your running it on and estimated weight etc? All this info will help someone here diagnose your problem.

[shesha]

my boat is 28 skater with twin 250xs, 32X15 props. my engine just refuse to go above 4000 rpm. so i changed the props to smaller one's and nothing changed. no sensore alarm issues ate all. i dont know what wrong ??? any help or starting point will help.. i changed the fuel filters . spark plugs. fuel hoses. but nothing changed. i checked the comperssion and all are good .

[Revolution141]

Sounds like the motors are in guardian mode. Not sure why both would be but it certainly points to an issue with something common to both motors eg. Fuel, battery?
check battery connections. Are you running smartcraft?
May need a merc diagnostic computer to get to the bottom of this. Definitely not gear ratio however.

[strokerdean]

When I changed to1.62 gears from 1.75 the rpm dropped 400/500 with the same size prop.

[shesha]

yes i am runing a smart craft. but no unknow alarms issues. :| i have decided to empty all the fuel in the tanks and start againe. ???