Mercruiser 4.3 maxes out at 2200 RPMs at WOT - Please Help.

[alldodge]

You know it could be your engine got a knock signal, and if this is the case the engine timing will retard and you will loose power. I think you need to have the engine scanned

 

[Scott Danforth]

I have a good friend and former co-worker with a 4.3 in his boat. he lost a plug and had both shutters drop in the y-pipe plugging up the exhaust. he couldnt get to WOT, and the dealer even gave him other props to try.

 

[acevedor2]

I have a good friend and former co-worker with a 4.3 in his boat. he lost a plug and had both shutters drop in the y-pipe plugging up the exhaust. he couldnt get to WOT, and the dealer even gave him other props to try.

Thanks! I am definitely going to check those first. I checked the air cleaner today and both butterflies open at WOT and both jets squirt fuel. I also confirmed the anti-syphon valve is a 1/4" NPT fitting and will pick one of those up this week as well.

If when I open up the exhausts, the flappers aren't there - where will they go and how can I get them out? Do I have to remove the outdrive to get to them?

Finally, how do I cross-check by serial what flapper part number I need?

 

[nateo]

I belive you should be idleing at 650 not 600. Id break out compression gauge, then timing gun. May sound like a pain but really only takes about 15 min.

https://www.perfprotech.com/blog/tech-specs/mercruiser-v6-marine-engine-specifications

 

[acevedor2]

If you remove the outdrive, you can stick a water nozzle to the water inlet. A large diameter hose with a good pressure could allow higher rpms?

It is between 600 and 650. I am eyeballing based on gauge graduations. I agree though that it is still a good idea to check the timing. I'll probably check compression as well. It's a PIT Ain this thing though because the sides of the motor (plugs) are not as easy to get to in this boat...

 

[acevedor2]

Ok - think I might have found the problem but need a little more help. I pulled the exhaust to check out the flappers and they are toast. I'll post pics shortly, but the port side had only the cross bar still there, no flaps. The starboard side was in tact allbeit a little bit charred....

I was able to put a small camera down and fish out one of the flaps from the port side. I cannot, however see far enough or locate the other flap. So I assume that piece is still down there and probably still clogging things up. How do I locate it? I have an inspection camera but the lens is just a little too wide to get down there all the way. It can't have gone through the exhaust, I do not believe because it is a fairly big piece of metal/rubber. Thoughts? Thanks!

 

[bruceb58]

May have to take the drive off. It will be lodged down there.

 

[acevedor2]

May have to take the drive off. It will be lodged down there.

I guess that's my question. If I pull the drive off, will I be able to see the exhaust collector and see if the piece is there or will I have to remove other pieces as well? I did manage to get the inspection camera from one side of the y to the other and did not see the piece. I know that it can't have disappeared though. Is it possible it's caught in the very bottom of the y where it goes into the outdrive/exhaust? I won't feel comfortable starting this thing up if don't know where that piece is is...

 

[poconojoe]

I have a 2003 merc 4.3L and one of my exhaust shutters made it all the way into my outdrive. I found it when I split the drive to do the impeller. It was just the inner metal plate. All the rubber was gone. Mine was part # 807166A-1. Get one of the old ones out and measure it. There are a few different ones.

 

[poconojoe]

Hey guys, could his rpm problems have been caused by water backing up into the engine?

 

[acevedor2]

I have a 2003 merc 4.3L and one of my exhaust shutters made it all the way into my outdrive. I found it when I split the drive to do the impeller. It was just the inner metal plate. All the rubber was gone. Mine was part # 807166A-1. Get one of the old ones out and measure it. There are a few different ones.

I have the serial number for the engine and the local marine places have them in stock - they are $60 a pop! That said, I need to find that last piece first before I decide to put it back together. I am a little OCD...Plus I don't want to ruin the engine. What is the correct steps I should take now to locate it? I am a long time car guy so I am mechanically inclined, but this is my first boat. Appreciate the help.

 

[alldodge]

I guess that's my question. If I pull the drive off, will I be able to see the exhaust collector and see if the piece is there or will I have to remove other pieces as well?

If it's in there then yes you will be able to see it, that is unless it was small enough to be spit out through the prop

I did manage to get the inspection camera from one side of the y to the other and did not see the piece. I know that it can't have disappeared though. Is it possible it's caught in the very bottom of the y where it goes into the outdrive/exhaust? I won't feel comfortable starting this thing up if don't know where that piece is is...

Going from one side to the other and not seeing anything else you have a good chance the other piece is gone

 

[acevedor2]

If it's in there then yes you will be able to see it, that is unless it was small enough to be spit out through the prop



Going from one side to the other and not seeing anything else you have a good chance the other piece is gone

I think you're right that it is likely not in there anymore, what concerns me is that there is almost no chance that piece came out of the small exhaust ports. How likely is it that mine did what poconojoe's did and made it's way back to the lower unit of the outdrive? Also - I am still looking for an answer to the question of - if I pull the stern drive, will I be able to see where the ypipe exits?

I did put my air hose nozzle up those two exhaust ports from the stern and blew into them with quite a bit of air. Still nothing with the inspection camera after that. I am trying to pull a good diagram of the entire exhaust system so I can see the flow and get some idea of where it could have gone. Long shot as well, but anyway it might have been pushed up into the riser/manifold? I am thinking no because the one flap I did find was down the y-pipe.

 

[acevedor2]

One additional question because I have gotten conflicting advice - could this be my issue? In other words, could the exhaust clogged by the flapper cause my low WOT throttle issue? Some have said that it would only impact a few hundred RPM, not the couple of thousand RPM I am off right now.

 

[alldodge]

One additional question because I have gotten conflicting advice - could this be my issue? In other words, could the exhaust clogged by the flapper cause my low WOT throttle issue? Some have said that it would only impact a few hundred RPM, not the couple of thousand RPM I am off right now.

Depends on how much the piece is restricting the exhaust. Only one way to find out and split the drive

 

[acevedor2]

Thanks Dodge. That's what I have planned for Friday. I am picking up the shutters and a new impeller tomorrow. I just did it a year and a half ago, but there are mixed thoughts as to how often it should be done. I have heard annually and I have also heard every other year. If when I split the drive I do not find the piece, I intend on pulling the leg to see it ended up in there. If so, I might as well do the impeller at the same time. I will also be doing the compression testing and checking the timing. Does anyone know what the correct timing should be for this motor? I did not see it in the manual. I am sure it is there, I just can't seem to find it.

Thanks again!

 

[Eric 3.7LX Alpha 1]

How about the inline fuel filter at the carb inlet. You mentioned you replaced the fuel filter in the 1st post... which one.... the fuel water separator or the inlet filter at the carb?

 

[alldodge]

Most with alpha 1's change every two years, some do longer. The gen 2 I have been told can go 5 to 7 years

 

[acevedor2]

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How about the inline fuel filter at the carb inlet. You mentioned you replaced the fuel filter in the 1st post... which one.... the fuel water separator or the inlet filter at the carb?

The fuel/water separator. I'll have to take a look at the other one. I have never replaced that one in the 3 1/2 years I have owned the boat. I honestly don't remember seeing it, but I am assuming it's there...

 

[Eric 3.7LX Alpha 1]

Remove the fuel line off the carb should be a 5/8" wrench I believe and then the large nut at the carb inlet... 1" wrench on that one..

Filter is under the large nut with a spring in there also just keep an eye on the orientation.

Some have a screen can be washed out with carb cleaner and reused..... some have paper element and would have to be replaced.