Issues: gimbal, ecu, who knows….

[2ridgebacks]

Long story short, I broke down about 3 miles from the ramp. Had been running about 3400 rpm. Engine gained rpm similar to prop cavitation, I pulled back on the throttle, and the boat settled dead in the water. Would not crank. After a few minutes it would fire and the rpm would immediately increase to near WOT before I could shut it off. Sometimes it wouldn’t crank ( like in a bind) sometimes it would start and rpm would climb.
What I know
2013 8.1gi catalytic engine.

Throttle is electronic. Linkage to an encoder on the intake, short harness to actuator on throttle body. Does that
Mean electronic shift? Throttle plate is completely shut as rpm climbs.

With the binding, I’m thinking water in the cylinders. Pulled all plugs. No sign of water.

I’m also thinking maybe the gimbal failed. When I look down on the rear of the motor, I can see a short section of splines through a slot in the adapter. Is this normal? How could a gimbal affect throttle?

Both batteries were dead before we went out. Wouldn’t run the blower dead. I charged them for a couple of hours. The boat started fine at the ramp. If there was a low voltage issue, would that goof the ecu?

I’m really at a loss on this one as the issues don’t relate to each other. At least not that I can see.

[Big Block Power]

That sucks man. No the gimbal shouldn't matter. Mine went out last year it just vibrated. If the coupler goes out the boat won't move. Maybe a bad vacuum leak? Intake gaskets? Doubt it though. Maybe bad iac motor. I keep spares in my boat. It's a easy change. Ecu won't fail from dead battery. I know it's hard but can you hear loud sucking from anywhere else other than the throttle body.

[2ridgebacks]

No, no sucking sounds. Nothing is obvious or easy as a vacuum leak. There is an intermittent knocking. Not a rod or main knock, but something that Mike makes sense if the gimbal came apart on the input or output

[2ridgebacks]

That does not explain the high rpm issue though

[Big Block Power]

That does not explain the high rpm issue though

No but a stuck wide open iac valve will. No codes or warnings? Without a scan tool it's all guessing.

[2ridgebacks]

No warning. 500 hrs on the motor and gimbal. If tue iac had a minimum mechanical opening that would set normal idle in neutral and you removed tue load of tue input to tye out drive, that would cause a significant increase in rpm.? I know electronically it is looking for an rpm. But, are they installed with no opening or is there a minimu mechanical opening?

[Big Block Power]

No warning. 500 hrs on the motor and gimbal. If tue iac had a minimum mechanical opening that would set normal idle in neutral and you removed tue load of tue input to tye out drive, that would cause a significant increase in rpm.? I know electronically it is looking for an rpm. But, are they installed with no opening or is there a minimu mechanical opening?

They have a pintal valve that moves on and out. If it's all the way it is letting in full about of air and high idle speed. You can remove your spark arrestor and look in the opening where the pintal would be. Possibly. I'm only speculating. I'm pretty sure on mine you would be able to see it.
It would be nice to know if the boat would go forward and backwards though too. That would eliminate a bad coupler. Plus when those go bad you smell burning rubber.plus it would be nice to know what the tps is reading.