Wot issue

[HudsonRiver77]

Hello everyone, this is my first post and looking for some opinions I recently purchased a 2007 crownline with 5.7 MPI and Bravo 3 outdrive Shortly after purchase it hydrolocked on port side due to bad exhaust manifold from saltwater use.. Anyway had both sides replaced and mechanic also discovered left side had low compression so they pulled the head and it was slightly warped so they had it shaved and valves reseated...now to my problem.. When I run at WOT, an alarm beeps and I reach about 4,400 RPMs and the motor starts to kind of surge..wondering if it's rev limiter but I'm only getting 45 mph on GPS and pretty sure before the work was done I would get around 52 mph and never felt that motor "surge" feeling or heard the warning alarm.. As soon as I put throttle in neutral the alarm goes away. It Plaines off great and will run great constantly at anywhere from 3,000 - 4,000 rpm range but I do here the beep occasionally while accelerating but doesn't stay on solid until max throttle. Temp Guage stays good around 155-160 degrees and oil pressure stays steady at 60 psi. Could I be hitting rev limiter and I did read that the alarm Wil beep when hitting rev limiter. Not sure what top rmp should max out on this motor Any help or idea is greatly appreciated

 

[alldodge]

What is your motor serial number?
Do you have mechanical or digital controls?

A boat tachometer has a 50/50 chance of being accurate. Don't know if your hitting the rev limit, but once hit, it will reset if the throttle is brought back to 3500 or so, there is no need to go to neutral to reset.

It could be the water pressure sensor or a few others. Best way to find out what the motor is doing is to have it scanned for codes

 

[HudsonRiver77]

Serial number is 0W677543 and analog gauges..yss sometimes beep will stop when bringing back the throttle some but most times have to go in neutral and then I can continue on no problem and no beep as long as I don't go WOT..but also nit sure about the motor "surging" feel unless the warning sensor for low water pressure would try to limit the engine some??

 

[alldodge]

I mentioned digital shift, which means you would not have cables going from the throttle handle to the motor. You probably have the standard cable shift type

You said a beep and I'm assuming a constant beep and not 2 beeps every so many seconds.
Its best to scan motor for codes to see which it is

If so, its probably the water pressure switch, but can also be another like the gear shift switch (not rev limiter). If its the gear shift switch, its on the shift bracket in the pic below. I doubt this is the issue because it doesn't happen until your at WOT. To test, unplug the switch and if it still comes on then its not that. Note: this pic also shows an interrupt switch, and you will not have one of these

The water pressure switch is on the power steering cooler (item 16 in link)
https://www.mercruiserparts.com/bam/subassembly/31751/12840/280

 

[achris]

Without scanning the engine for codes, we are all just guessing at want to problem could be.

As AD suggested it could be that the gear inductor switch is not plugged in, or broken, or out of adjustment. Or it could be the IAC valve, or the seawater pressure sensor. Or any one of a dozen other things. You need to have a computer connected to the engine to find out why it's going into guardian mode.

Chris....

 

[QBhoy]

As said. You need to get some codes read. Could be loads of things. If the tacho is anywhere near accurate it’s not the Rev limiter. Your engine is about 5100 or just over for that. Trust me, I’ve hit it.
Ive had all the usual mpi issues come and go and the only one that actually beeped at me so far was the IAC error.
That said. Amongst them all, I think I had a beep or two then it showed cylinder missfirws on the smart craft. This was down to the old crap cap.
other causes of surging are fuel regulator gone bad. The most recent one I had to solve was the shift interrupt switch being activated at wot because the throttle mechanism was occasionally coming into contact with this. You would know all about it if it was this though. It cuts the cylinders down to 4 for a split second and almost fired me through the windscreen.

 

[achris]

.... It cuts the cylinders down to 4 for a split second and almost fired me through the windscreen.

That reminds me of a funny story.

Many years ago, when I was a younger man..... I was on an OMC outboard course. That was just after OMC had introduced S.L.O.W, speed limit overheat warning, on their outboards. After getting reports of SLOW kicking in and sending all the occupants of the boat flying forward, OMC changed the programming to reduce the engine speed, on an overheat, gradually... We called it slow SLOW......

Chris...

 

[QBhoy]

That reminds me of a funny story.

Many years ago, when I was a younger man..... I was on an OMC outboard course. That was just after OMC introduced S.L.O.W, speed limit overheat warning, on their outboard. After getting reports of SLOW kicking in and sending all the occupants of the boat flying forward, OMC changed the programming to reduce the engine speed, on an overheat, gradually... We called it slow SLOW......

Chris...

Haha. Had a wee Chuckle at that Chris.
Yeah. It was bothering me most of the season this bloody issue. Last thing I thought it would be and hard to diagnose, replicate the fault or watch what’s going on under the hood when it only happens at wot and at bloody mid 60’s, haha. Finally solved it just before the end of the season. Typical. The boat is running better than ever now and posted some record results, even with the seasons hull growth dragging. Mainly down to the new prop. Can’t wait for next season already.

 

[achris]

Ouch. Can't imagine trying to diagnose a problem, especially a sudden power cut, at mid 60s. My boat will do 50, and at that speed about the only thing you're doing is looking for something to hang on to and trying to stay upright....

 

[QBhoy]

Exactly. So you can imagine my struggle. Only when I thought about what it was actually doing I figured it.
And after a pointless plug, lead and diz change !

 

[achris]

...And after a pointless plug, lead and diz change !

:facepalm: of course it was pointless, it's electronic ignition. :lol::lol::lol:

Chris...
Sorry, couldn't resist...

 

[QBhoy]

You’re right. Was at the end of my tether.