Have you ever heard of this??

97 SNOB.........GT 40. After 15 minutes or so on the water, I get a HORRIBLE vibration from the back of the boat. I had a buddy drive it while it was doing it so I could listen from the back. You can feel the vibration in the floor on either side of the motor box just in front of the rear seat. The vibration comes in at about 2300 RPMs, and continues until you drop back down to idol. You can't accelerate out of it, either. The only way to make it stop is to cut the throttle. It will do it every time you get back on it, unless you idle around for 10 or 15 minutes. Then it's good for another 10 minutes or so, then the vibration is back.

The best theory I could come up with is that the tail bearing in the transmission is bad. It makes sense to me, that maybe the bearing is rusty, and flinging the fluid off of it after a while. Then, once it lubes itself back up, it's quiet for a short time again.

I contacted Correct Craft, and my marina and neither one of them think it's a bearing. The marina doesn't know, or really care, and Correct Craft says 99 times out of 100, it's that the transmission is out of allignment. Before I make the hour and a half tow to Midwest CC, has anyone else had anything like this before? Sorry for the long post, but I'm ready to ski!!!!!!!!! HELP!!!!!!!!!!    Also, do you think it's hurting it when it's doing this? I'm afraid to ski with it because I don't want to make it worse.

Also check the strut they used extra long strut bolts and came loose. Check the rudder for excessive play.

Check to make sure the prop shaft bolts to the transmission are tight. I had the same problem once after I had replaced a bent shaft. I didn't get the "collar" tight and snug against the transmission and experienced much of what you described.

Rleinen79 -- Yes!!! The same thing is happening to me!

When my boat hits 23,000 RPMs (PCM 93-07276 Model 40 Pro-Boss engine) the entire boat shakes and the engine shutters, making a duh, duh, duh, duh, duh, duh noise and I cannot get through it. Here’s the perplexing part. It only does it after the boat is warmed up, just like you. If I start the boat up first thing in the morning and take it for a spin, it’ll zip along at 40 MPH no problem. Give it about a half an hour and I won’t be able to get it past 23,000 RPMs.

Here’s what I (we’ve) tried so far. I replaced all of the spark plug wires (and plugs too), thinking there was a short causing one of the cylinders to miss. Then we replaced the water pump, thinking the engine was getting too hot and the ECM was preventing the engine from overheating, shutting it down. Then we replaced the alternator, thinking maybe it wasn’t putting out enough juice to run the computer. Now my mechanic is thinking that maybe it’s a fuel problem and as I write this, he’s taking out the fuel tank, cleaning it, making sure it’s not clogged in any way and will work his way up system.

Did you solve your problem? If so, what did you do? I'm hoping like heck you found a solution! Please let me know.

Jim:

aah, that would be 2300 rpm's which is about the point that the limp mode kicks in on a '93 boat with Pro Tec. I am guessing '93 from the serial (?) number you list. If not Pro Tec, then no limp mode. You might want to focus on the temperature switch that activates limp mode since you say it happens only when warm.

Hi David,

Thanks for the tip on the temperature switch, I passed it along to my boat doctor. And yes you are correct it does have Pro Tec. The model year of the boat is a 94, so it doesn't surprise me that it's a 93 model engine.

Thanks! You're awesome.