496HO issue - won't rev past 3,400 rpms

[tomahdonzi]

I had an issue with my 496HO this weekend. As I attempted to get on plane, everything was fine until I reached about 3,400 rpms. Then I got a solid beep from the motor, and it gradually took the rpm's back down to idle. At first, I was able to resolve the issue by powering down the boat and batteries, and then restarting. Once I got past this issue, boat and motor ran great. But after a day of this, it now shuts me down everytime I reach about 3,400 rpms. I took it over to the dealer yesterday for them to put on computer, but haven't heard back yet. Was just wondering if anyone else has run accross this.

Rick

[Baja 272]

Any word back from your dealer?

[tomahdonzi]

Yes, heard back from dealer. Low Water Pressure. Also manifold temp warning. So we think it's the water pump. Putting a new one on as we speak. Hopefully that is it.

[Baja 272]

Sea pump or engine water pump bad? Mine also has a solid beep will not WOT.

[DynojetResearch]

Yes, heard back from dealer. Low Water Pressure. Also manifold temp warning. So we think it's the water pump. Putting a new one on as we speak. Hopefully that is it.

A friend of mine had the same issue with his 496HO in a 25' Eliminator. Turns out the inlet was mostly plugged going into the water pump.

If your new pump doesn't fix it, take a look at the piping and inlet to the pump.

[Expensive Date]

If the water pressure is not it a bad neutral safety switch will trigger an alarm at 3500.

[tomahdonzi]

Well, got the boat back from dealer. They replaced water pump, and ran it in their test pool for 30 minutes. Ran fine. Casing on the old water pump was pretty much destroyed. So the water pump was necessary, and I thought it would fix the problem. Today I launched it and same damn problem occurred. Had a single beep while idling away from launch ramp, then solid beep at 3,400 rpm while planing, and guardian mode again! As I rack my brain trying to think what might be causing it, here is what I'm coming up with. I'd like to get anyone's thoughts on this.

I have never had this problem before with this boat. I bought it in 2010 with 35 hours on it. This last winter, we replaced the Bennett Trim tabs with Mercury K-Planes (280's). I also added mechanical indicators for the tabs and the drive with a Livorsi unit. Finally, I replaced the stereo. While at the dealer, they also changed the impeller in the water pump.

Anyway, first time with the boat this spring, my first time getting on plane went just fine. I put the tabs all the way down prior to plane, then moved them up after plane. The next few times that day as I was getting on plane, I noticed the engine stumbling around 3,200. The engine worked through it and once it moved past that rpm level, it ran great. This problem persisted throughout the summer, although it would only happen intermittently. I only had this issue as I was trying to get on plane. Once on plane, I could take the rpms down to 3,000 and no engine issues.

Then last week the current issue. It doesn't stumble at all, but just goes into guardian mode on take-off at around 3,400 rpms.

I'm wondering if it has something to do with the K-Planes. I wonder if there is some kind of voltage spike on take-off that is causing this. Or maybe something with the mechanical indicators (like a loose connection or something).

I just don't see how it could be mechanical at this point, if the dealer runs it just fine in their drive pool, but then on the water while I'm trying to plane, I get this issue.

We are going to put it back on computer tomorrow. Might just take it back to the dealer who did the work on it this winter (they are 3 hours away, and that's why I'm using a different dealer on this issue) and tell them to fix the damn thing before they give it back to me.

Any interesting thoughts on this fricking problem. My wife is losing all interest in boating at this point.

[Sydwayz]

Salt water boat?

I seriously doubt it's the K-Planes, but if you want to rule them out, flip the breakers for them off, or pull fuses.

What kind of boat? Does it have a fresh water flush hose connection? This is been discussed a few times here on the board. Do a search. Some of the manufacturers, like Baja put check-ball valve T's in the SWP line, and the check ball system gets all gummed up with seaweed and or sand, and will cause your same condition.

Do you have any water in the bilge? You could have one of the air pump water evacuation actuators going bad.

Do you have a water pressure gauge? How about a water temp gauge? What do they say? Are either of your manifold hotter than the other?

Last, do a search here on Rinda or go to their website. If you own any engine with SmartCraft (like yours), its a HUGELY wise investment to have your own scanner.

[rw40426]

If the water pressure is not it a bad neutral safety switch will trigger an alarm at 3500.

+1 Had this issue with mine and it was the neutral safety switch that loosened up causing the switch to barely make contact. The scan tool should reveal an over rev code and it can tell you which position the shifter was in when it happened. When I hit some waves the switch would flicker a little causing the alarm to randomly come on and off. I adjusted the switch to make better contact and have not had any issues since.

[tomahdonzi]

The boat I have is a 2008 Donzi 27ZR. It's used in fresh water. It does have Fresh water flush system. I have a water temp gauge. It's reading normal.

I guess the thing that I don't understand is this. It ran fine in the dealer's drive pool. I think they back the boat into it so the rear unit is in the water, then they run it in gear above 3,000 rpms for something like 30 minutes, and no issues. Then I go out on the water, and when I try to plane, I get the alarm.

I am noticing some water in the bilge, although I didn't check it after this last run. It's not a lot of water, and I just figured it was from coming off plane and getting some water coming over the stern into the engine compartment. But maybe we could look at that.

I'll know more tomorrow morning when the dealer scans the motor.