'15 G23 PCM 409 revs in neutral

[JSM]

After idling out about 10 min to surf. Hit throttle to tow and boat died. Restarted and noticed engine temp at 175. Hit throttle again, tried to go and then died. Turned power off and waited 1 minute. Started back up. Temp down a bit but boat starts to rev (not allot) in neutral. High Temp warning comes on with temp back up to 175. Killed it again waited 5 minutes and then poked back to dock - temp comes down to 169. When I took it out of gear it starts to rev even higher. Unfortunately I had to pop it in and out of gear while reving because I had to get it into dock. Checked intake and water strainer. All clear. Impeller and all fluids serviced by dealer in December. As a side note in case seems related to someone, two days before we were cruising at 25 mph when the gear shift started to shutter and boat lost momentum but never power. Looked back saw a log we figured I hit. Boat ran fine afterward. Inspection of prop, shaft et al looked good. No issues the next two 3 days running 5 hours a day. Boat has about 200 hours

So - any thoughts on the cause assuming the impeller is good?

[Infinity]

After idling out about 10 min to surf. Hit throttle to tow and boat died. Restarted and noticed engine temp at 175. Hit throttle again, tried to go and then died. Turned power off and waited 1 minute. Started back up. Temp down a bit but boat starts to rev (not allot) in neutral. High Temp warning comes on with temp back up to 175. Killed it again waited 5 minutes and then poked back to dock - temp comes down to 169. When I took it out of gear it starts to rev even higher. Unfortunately I had to pop it in and out of gear while reving because I had to get it into dock. Checked intake and water strainer. All clear. Impeller and all fluids serviced by dealer in December. As a side note in case seems related to someone, two days before we were cruising at 25 mph when the gear shift started to shutter and boat lost momentum but never power. Looked back saw a log we figured I hit. Boat ran fine afterward. Inspection of prop, shaft et al looked good. No issues the next two 3 days running 5 hours a day. Boat has about 200 hours

So - any thoughts on the cause assuming the impeller is good?

Hi temp warning at 175? I have the ZR409 in my boat and normal operating temps are between 168-173...
Being a fuel injected boat, strange for the revs to happen like that in neutral, wondering if something going on with fuel system, fuel pump, perhaps a partial blockage that its trying to over compensate for to overcome, etc? Just out of curiosity, do you run regular ethenol fuel and has boat sat for extended period?

Do you do any DIY.... Are you comfortable double checking all your fluids, as well as the impeller? Not hard at all in that engine, just PITA to access since you gotta scrunch up in the rear locker...but you remove engine belt cover, remove engine belt by using 15mm socket on tensioner, then 3) 10mm bolts to remove the impeller housing so you can pull it out and inspect everything to make sure the impeller hub is not "spun" and/or any vanes missing. Perhaps something got thru system and damaged the impeller or one of the vanes, its worth checking for 30mins of work.

Maybe the temp reading was incorrect and why alarm went off or something is up with computer system which is what was causing things to go a little wonky with the boat shutting down, alarm going off, and rpm surging? Have you checked to see if any CODES in the system...with the temp alarm, there should be at least one, perhaps there is something else that will offer a clue? This one has me a bit confused....few things that do not make sense to me, course I am not a mechanic, just a DIY guy that happens to know this engine very well since its what I have.

[JSM]

Thanks for the reply. I used to DIY allot but have little interest now. Rather drink beer and drive boat. Dealer called me this morning and he was equally puzzled. Luckily they have outcall service. I’ll let you know what they find.