Massive vibrations...then none

[jonny rotten]

1990 4.3 Gen one drive.
It went out perfect. Then on the way back it idled fine but as soon as I gave it gas leaving the channel it had massive vibrations. the whole boat was shuttering. Immediatly dropped it back to idle. It happened 2 more times and I said it looks like where limping back to shore. Then 2 or three minutes later I tried it again and it ran perfect even at pretty good RPM and we cruised back. When it was happening it purred like a kitten at idle. The prop blade is kind of chewed up and I'm getting a new one but I would think that if it was the prop it would be an issue all the time...Could it have been from water getting in a cylinder (main concern) if the risers are going bad. Or possibly a head gasket. I've never overheated and it ran pefect on the muffs when I got back revving it up. I've had the boat 12 years and it's the first time anything like that has ever happened....I REALLY don't want to blow my motor up...could it be an outdrive issue? I should have revved it in nuetral while it was happening to possibly eliminate the outdrive but didn't think of it. Oddly my buddy hit the bilge pump button and maybe 2 gallons came out (5 seconds) and that's when I tried it again and it worked. He was saying the water threw something out of balance but I know that's not the case.

 

[Scott06]

Probably weeds on prop. Make sure you get the prop repaired or replaced if damaged

 

[tpenfield]

Tell us what engine/outdrive you have.

My first thought is that 1 (or more) cylinders were not firing. So maybe check all of your spark plug wires.

While you are at it you could remove the spark plugs for some inspection and to see if you find any water in the cylinders or an issue with the plugs.

You could also run a compression test to get an idea if the problem was a partial hydro-lock.

 

[jonny rotten]

Probably weeds on prop. Make sure you get the prop repaired or replaced if damaged

I boat in sandy areas with no real weeds but it's real shallow water and I bottom out alot. It didn't seem like a prop isse. As soon as I touched the throttle in gear the whole boat shuttered like if I didn't pull back something was going to blow

 

[Scott06]

I boat in sandy areas with no real weeds but it's real shallow water and I bottom out alot. It didn't seem like a prop isse. As soon as I touched the throttle in gear the whole boat shuttered like if I didn't pull back something was going to blow

But then it went away?

 

[jonny rotten]

But then it went away?

Yes...and ran flawless

 

[dubs283]

I'm gonna be the oddball (typical) and say power steering purge/bleed

 

[jonny rotten]

I'm gonna be the oddball (typical) and say power steering purge/bleed

It does have a power steering leak somewhere, I think the cooler, I top it off everythime I go out. It's been like that for years and never had an issue. Any details on how that would make it feel like something was going to explode.

 

[jonny rotten]

Also there was no knocking. Just massive shuttering and vibrations like something was about to blow

 

[nola mike]

My first thought is that 1 (or more) cylinders were not firing. So maybe check all of your spark plug wires.

Mine as well

 

[jonny rotten]

My first thought is that 1 (or more) cylinders were not firing. So maybe check all of your spark plug wires.

If I pulled one plug wire at idle it sould duplicate the issue if that was it right? Seems like a good way of testing/troubleshooting/eliminating

 

[flashback]

Water in the fuel?

 

[dave8311]

Would a faulty or mis adjusted shift interrupter cause this?

 

[Scott06]

Would a faulty or mis adjusted shift interrupter cause this?

No it would kill all spark

 

[Simoniz]

Probably weeds on prop. Make sure you get the prop repaired or replaced if damaged

I had similar once, wasn't like engine vibration coming from misfiring, rather the whole boat was shuddering, and the prop was slipping, as if it was venting air (trim too high). Turned out it was a plastic sack wrapped round the prop.