Mercruiser 3.0l cuts off at high revs.

[fat fanny]

Re: Mercruiser 3.0l cuts off at high revs.

With the vibration and bouncing around especially on a 3.0 I have found that a good by-weekly check of all electrical connections is a good PM to avoid such issues. Also before you start start it in the dark w/muffs on and look around all the connections and look for a blue colored spark wiggle wires and connections this may help isolate a bad connection, you should also do a continuity test on all plug wires.

 

[earlandamys180]

Re: Mercruiser 3.0l cuts off at high revs.

I had a very similar problem on my 98 3.0 and I did all the things you have done and still had the same problem and could not figure it out til one day when I was putting my blower hose back on with the stereo playing and I moved the blower hose and the stereo cut out and pointed me to the problem. There is I believe a 80 amp fuse that hangs on the positive lead to the starter that with all the vibration from the 3.0 it had caused the nut to back off and was laying in the bildge area causing a bad connection. Mine had been doing it long enough that it had arced out so much that it had ruined the treads on the fuse, I replaced the fuse and the problem was solved. May not be your problem but I would check there cause its sounds very similar to what mine was doing.

 

[gobbler boat]

Re: Mercruiser 3.0l cuts off at high revs.

1997 5.7 2 brl Merc. 350 hrs very well maintained. Boat has ran perfect for 11 years. Had a problem this summer w/ boat cutting out especially at high rpm's. After going through everything electrical/fuel, it ended up being the anti-siphon elbow on top of the fuel cell.

My mechanic had it off and blew in it and it seemed clear. When a different mechanic checked it, he actually picked around inside it and small pieces of debris fell out. We replaced it and the boat has ran fine ever since.

 

[virtual120]

Re: Mercruiser 3.0l cuts off at high revs.

I had a very similar problem on my 98 3.0 and I did all the things you have done and still had the same problem and could not figure it out til one day when I was putting my blower hose back on with the stereo playing and I moved the blower hose and the stereo cut out and pointed me to the problem. There is I believe a 80 amp fuse that hangs on the positive lead to the starter that with all the vibration from the 3.0 it had caused the nut to back off and was laying in the bildge area causing a bad connection. Mine had been doing it long enough that it had arced out so much that it had ruined the treads on the fuse, I replaced the fuse and the problem was solved. May not be your problem but I would check there cause its sounds very similar to what mine was doing.

So did you have the engine cutting out like I do and this was the problem you think ? or was it just the dials that were mucking up ?

Thanks. I have hope lol.

 

[Don S]

Re: Mercruiser 3.0l cuts off at high revs.

Go check your's. It only takes about 2 seconds.
You could have 2 seperate problems, and engine running problem and a guage problem. But you are going to have to leave the computer and start checking things and doing some testing, or you never will find out what's wrong.

 

[virtual120]

Re: Mercruiser 3.0l cuts off at high revs.

Go check your's. It only takes about 2 seconds.
You could have 2 seperate problems, and engine running problem and a guage problem. But you are going to have to leave the computer and start checking things and doing some testing, or you never will find out what's wrong.

LOL, ive been doing nothing else over the last few days - dont get me wrong, im not looking for people to do the work for me. Im presently taking the anti-siphon valve off to check it. Will let you know the outcome.

We are also going to take the tank out in a minute, empty it and then clean it. Here's hoping....

Thanks everyone for the answers, youve been really great.

Cheers
Tim

 

[Don S]

Re: Mercruiser 3.0l cuts off at high revs.

We are also going to take the tank out in a minute, empty it and then clean it.

There are tests you can make without going to all that work. Look above where I mentioned using an outboard tank to see what happens. Then there is the method using a gauge http://forums.iboats.com/showthread.php?t=283269
While it's ok to clean the tank, cleaning a clean tank that isn't the problem is just a lot of wasted time.

TROUBLESHOOT the problem, find the problem and fix it. Don't just start fixing and hoping and throwing time, money and parts at it for nothing.

 

[earlandamys180]

Re: Mercruiser 3.0l cuts off at high revs.

So did you have the engine cutting out like I do and this was the problem you think ? or was it just the dials that were mucking up ?

Thanks. I have hope lol.

Yes the engine cut out and ran like crap, plus the guages were doing some funny things cause it was a bad connection.And sometimes it would run like a champ for awhile.Thats why I said it may be your problem cause you said sometimes yours runs fine also. And like Don said its an easy check and dont feel bad if thats it cause my Sea Ray dealer told me once I found it that there were more than me that had spent more than I did and never found the problem.

 

[virtual120]

Re: Mercruiser 3.0l cuts off at high revs.

I was putting my blower hose back on with the stereo playing and I moved the blower hose and the stereo cut out

Do you mean you were in the engine bay putting the blower hose pipe back on or do you mean you were turning it on at the dashboard with the switch ?

There is I believe a 80 amp fuse that hangs on the positive lead to the starter

I can only see a 20amp fuse coming off a red wire which comes of the starter. This I have checked and it is fine.

We ran an external tank last evening straight to the fuel pump and it ran good. We then plugged all the fuel lines in back as normal and ran it again and it ran well. We thought we had cracked it but when we ran it up again today, after about 1 minute at 2300 revs it splattered and kaplonked and died again to an intermittent idle speed.

We are going to take it our on the water now and if we get the problem again, we will run an external tank straight to the pump. If that doesnt work we will take apart the fuel pump and check it out. Maybe there is a hole in the diaphram !

Cheers
Tim

 

[virtual120]

Re: Mercruiser 3.0l cuts off at high revs.

UPDATE

Took it out last night and had the same problem. After a few seconds the engine dies. Doesnt conk out but runs real slow. When throttleing off, it quickly recovers then we accelerate and after 20 odd seconds it does again.

So, we ran an external tank and had exactly the same problem.

Here's a breakdown of everything we have done to date:

New plugs
New ignition leads
Took it to mechanics to clean out carb (they found water in the bowl but after cleaning it out ran the boat again which I would have thought would put water back in !)
Compression test
Cleaned and checked all electrical points
Engine flush and new engine oil (by mechanics)
Ran external tank
Put large fuel seperator/fuel filter inline fuel pipe


We are going to take out the fuel pump today to inspect it. After that, we really have no other option but to have the lifters taken out and cleaned/replaced.

 

[Don S]

Re: Mercruiser 3.0l cuts off at high revs.

There is a filter in the fuel pump, has it ever been changed?
The filter is a stone type element, if it's had water in it before, it's probably plugged up. Which is why you keep repeating the problem.
Faulty lifters WILL NOT fail consitantly like you are describing.

 

[virtual120]

Re: Mercruiser 3.0l cuts off at high revs.

There is a filter in the fuel pump, has it ever been changed?
The filter is a stone type element, if it's had water in it before, it's probably plugged up. Which is why you keep repeating the problem.
Faulty lifters WILL NOT fail consitantly like you are describing.

Aha - we will check, thank you very much.

Cheers
Tim

 

[virtual120]

Re: Mercruiser 3.0l cuts off at high revs.

Hi again - Still need help - engine dying at high revs !

OK, over the last week or so we have done just about everything only to end up with the same problem. Here's a recap;

new plugs
new leads
checked antisyphon valve
new distributor rotor
cleaned distributor points
new fuel pump filter
cleaned out fuel pump
carb clean out
new inline fuel seperator fitted
engine flush and new oil
new starter motor (crapped out during all these problems)
all electric points cleaned and tested
extensive trips out to check all the above
ran on external fuel tank to see if it was water or dirt in the main tank


Took it out tonight after thinking we had cracked it as out of the water it ran perfectly, better than ever before. Went out on the water for a test and as soon as we go over 2000 revs average the engine dies to a spluttering mess. We throttle off and it recovers in a few seconds. It also did this under 2000 revs also. It will run throtteling for about 20 secs max befor dying off.

Do you think a new fuel pump might be the answer. We were thinking of also of replacing all the fuel line too.

 

[johnno351]

Re: Mercruiser 3.0l cuts off at high revs.

I'm having the same problem with a 350ci-260 hp, runs fine for an hour or so then the revs die off and if i drop the throttle back it will keep running and after a few sec's it will go again but keeps repeating the problem.
I took it out of the water thinking maybe it's getting low on fuel and stuck 20 gallons in it and it ran fine for 20 more min's till it did it again.

Just changed the fuel filter today to see if that was the cause but no difference.

The other day it started at about 3000rpm so I dropped it to 2000rpm then started at there and in the end wouldn't run above idol till it wouldn't run at all(not fun when at sea and trying to get back in).
But when I got home it ran fine on the ears, so after doing the filter I took it out and I thought it was good but after an hour started again.

When it's doing it if I try to throttle on it "pops" and backfires through the carb.
It sounds very similar to what yours is doing.

 

[Bondo]

Re: Mercruiser 3.0l cuts off at high revs.

Ayuh,.. Both of you, Check the fuel Pressure at the carb,...

 

[johnno351]

Re: Mercruiser 3.0l cuts off at high revs.

Yeah, I was thinking fuel pump from the first moment it did it, But I might try running a clean fresh fuel can to rule out crap in my tank.

 

[ENSIGN]

Re: Mercruiser 3.0l cuts off at high revs.

What about the filter in the carb? I would also check the float level and float drop settings,they may have changed upon reassembly

 

[Don S]

Re: Mercruiser 3.0l cuts off at high revs.

Johnno, you should start a new thread with your problem,

Ensign, who's problem are you repling too

 

[frank246]

Re: Mercruiser 3.0l cuts off at high revs.

Have you checked the mechanical advance mechanisme in the distributor?
I have had kinda similar problem last season on a L6, a sticky advance mechanisme didn`t advance synchrone with the engine rpm so engine ran bad until the mechanisme came loose, same thing when decreasing rpm the advance stayed high # untill tapping the distributor. Some put grease on the swing weight shafts, the bushings are brass and only may be oiled caused the problem.
Just a thought.
Good luck

 

[wl6]

Re: Mercruiser 3.0l cuts off at high revs.

Have a 1986 Mercruiser 470 with very similar problem.Found the filter in the anti-syphon pick up tube and it was completely plugged, full of debris. Since you tried running on external tank and had the same issues I would check fuel pump and filter and probably get carb rebuild kit for the accelerator pump. Sounds like you did everything but paint the bottom.