All of the sudden low WOT (after hitting a wake)

[juice69]

Went out this afternoon, and the boat ran perfectly on the way out, which is about 10 miles one way. On the way back (after traveling about 2 miles), we hit a small wake from another boat - which we slowed down as normal so none of us ended up with broken backs - the boat was surging and wouldn't get over 3500 rpms at wot. I thought something might be up with the prop, but that wasn't the case. Checked all the spark plug wires, and they were all connected properly. So we limped back home at about 3000 rpms, and when I adjusted the trim it did seem to surge a little.


Back home on land, and after cleaning everything up, I pulled the prop and everything looked fine. Had a new thrust washer from a new prop that I never used, so greased the splines up and put that all back together.

I pulled the spark plugs and they did look like they could use a changing, but nothing terribly bad.

Pulled the fuel/water filter, which seemed fine (I've seen worse, which usually causes more problems at idle that I don't have). I did put fresh gas in today, but that doesn't seem to be the issue as the fuel filter was fine.

Checked oil, and that is fine - proper level and looks good.

I just cleaned the flame arrestor about 3 weeks ago, so that shouldn't be a problem.

I checked out the sticky in the adults only, and i'm not sure where to dig into next??? This just seems like it should be a fairly easy fix, but need someones advice on where to look next?

The engine is a 2004 3.0 mercruiser, with the alpha 1.

 

[juice69]

Re: All of the sudden low WOT (after hitting a wake)

I think I may have found the problem, but cant test it until I can get back on the water. As I was putting on the new fuel filter, I noticed that power steering belt didn't look all that tight - which it wasn't as the bolt holding the arm on to provide tension had fallen off (as in when we hit the wake). As the power steering pump belt also circulates water, my guess is this was/is the cause of the low rpms at wot. If I understand this engine correctly, there probably wasn't enough water/steam being forced out of the exhaust when the engine was turning fast, and the temp was sending ok as the impeller was pushing just enough cool water up to thermostat.

I guess I have 3 questions for those much more knowledgeable than I (i.e. bondo, chris, don s, etc):

1 - Could this (not getting water circulating through the engine, and a potentially too hot engine) have caused the low rpms at wot? I can't test this until maybe tomorrow or Thursday.
2 - The bolt has to be in the bilge, but in case I can't reach it, what size would be the replacement?
3 - Should I look (or be looking) for any related damage?

Thanks again everyone.

 

[alldodge]

Re: All of the sudden low WOT (after hitting a wake)

Wish I knew what type (EFI/Carb) engine we were working on. If this is an EFI may want to see if your knock sensor is telling the engine to retard timing. Pull the wire off the knock sensor and see if you get your rpm back.

BTW - My opinion
1 No
2 serial number
3 don't think so

 

[juice69]

Re: All of the sudden low WOT (after hitting a wake)

Hey Dodge,

It's a carb engine (serial 0W03140). I found the screw (and washer!) to the power steering pump, so cross that off.

If the circulating pump wasn't pushing the water fast enough through the engine to create exhaust, wouldn't that affect top speed? On Don's sticky, it says to rule out #8 - restricted exhaust and #13 - engine overheating.

I replaced the plugs and they were starting to turn a little white, but not terrible - seen worse (and better!).

 

[alldodge]

Re: All of the sudden low WOT (after hitting a wake)

Hey Dodge,

It's a carb engine (serial 0W03140). I found the screw (and washer!) to the power steering pump, so cross that off.

If the circulating pump wasn't pushing the water fast enough through the engine to create exhaust, wouldn't that affect top speed? On Don's sticky, it says to rule out #8 - restricted exhaust and #13 - engine overheating.

I replaced the plugs and they were starting to turn a little white, but not terrible - seen worse (and better!).

The serial number is not correct should be a zero, letter, followed by 6 numbers

If the water isn't moving fast enough this would not effect WOT so long as the engine was not over heating, then NO

Slight white on plugs sounds good, maybe a bit on the lean side but OK

With all else being the same I would start looking at fuel delivery issues which include, restrictions, float level, clogged jets

 

[juice69]

Re: All of the sudden low WOT (after hitting a wake)

Not sure where I pulled that serial number. It should be 0W038427.

The boat is 8 years old, and it certainly wouldn't hurt to clean the carb. Although, I do run the boat fairly regularly (im in s fla).

It's very odd that the boat could go from running fine to poor so quickly while underway (after hitting a wake). It does seem logical that something could've broken free and clogged up a jet, though. I was going off the boats temp gauge, so I can't definitively rule out overheat at high rpms. I'm trying to be optimistically positive, I think!

Question - if I could hit 4500 rpms while in neutral (in the water, not on muffs), would that rule out the carb?

I'll give the boat a spin tomorrow or Thursday and see if I need to jump into the carb/fuel side of the problem.

 

[imaxeman69]

Re: All of the sudden low WOT (after hitting a wake)

Could have knocked loose some debris into the carb from the fuel line, or into the fuel line from the fuel pump. Still sounds to me like a fuel issue.

 

[Levinz11]

Re: All of the sudden low WOT (after hitting a wake)

Went out this afternoon, and the boat ran perfectly on the way out, which is about 10 miles one way. On the way back (after traveling about 2 miles), we hit a small wake from another boat - which we slowed down as normal so none of us ended up with broken backs - the boat was surging and wouldn't get over 3500 rpms at wot. I thought something might be up with the prop, but that wasn't the case. Checked all the spark plug wires, and they were all connected properly. So we limped back home at about 3000 rpms, and when I adjusted the trim it did seem to surge a little.

Back home on land, and after cleaning everything up, I pulled the prop and everything looked fine. Had a new thrust washer from a new prop that I never used, so greased the splines up and put that all back together.

I pulled the spark plugs and they did look like they could use a changing, but nothing terribly bad.

Pulled the fuel/water filter, which seemed fine (I've seen worse, which usually causes more problems at idle that I don't have). I did put fresh gas in today, but that doesn't seem to be the issue as the fuel filter was fine.

Checked oil, and that is fine - proper level and looks good.

I just cleaned the flame arrestor about 3 weeks ago, so that shouldn't be a problem.

I checked out the sticky in the adults only, and i'm not sure where to dig into next??? This just seems like it should be a fairly easy fix, but need someones advice on where to look next?

The engine is a 2004 3.0 mercruiser, with the alpha 1.

This statement right here sounds like an electrical connection might have bumped loose.

My old boat drops rpm slightly when using the trim and my dash V gauge never really works right. I need to do a full rewire sometime.

 

[BRG25]

Re: All of the sudden low WOT (after hitting a wake)

Is the alternator working? Belt tight? If it's not and the battery is dead, the engine will stumble when adjusting the trim.

 

[alldodge]

Re: All of the sudden low WOT (after hitting a wake)

It should be 0W038427.

It's very odd that the boat could go from running fine to poor so quickly while underway (after hitting a wake). It does seem logical that something could've broken free and clogged up a jet, though. I was going off the boats temp gauge, so I can't definitively rule out overheat at high rpms. I'm trying to be optimistically positive, I think!

Question - if I could hit 4500 rpms while in neutral (in the water, not on muffs), would that rule out the carb?

I don't think it was overheating, and the serial number is correct. DO you know if this is a TKS model carb setup. If so it can through a couple other issues into the mix, but still sounds like a fuel issue.

Hitting 4500 RPM in netural you use a dropper full of fuel, running 4500 RPM in gear and on plane your burning about a gallon of fuel every 10 minutes. You need a lot of fuel in gear rell fast to saty running. So it would not runle out the carb.

 

[juice69]

Re: All of the sudden low WOT (after hitting a wake)

Not sure why my reply didn't post, but thanks everyone - it was electrical. I'm almost embarrassed to tell the tale. On the starter, there's a fuse that goes in front of the main of battery connection. Apparently, someone didn't tighten it enough when they put it back on, and that last wake we hit must've broke it loose just enough. Engine now runs at full rpms under load, and never sounded better with the new plugs/wires & fuel filter!