4.3l EFI Mercruiser high speed issues

[bluewaterboater]

I have a 1999 Sea Ray 190 with a 4.3l EFI engine in it. The motor only has about 175 original hours on it. The first 8 hours this season it has run flawlessly but lately I have been having some issues when I am running full out. At high speeds at WOT the motor seems to stutter a bit and loose power. Once I throttle down to about 35mph or so everything runs smoothly. I had my mechanic come down and change the fuel filter/water separator and took it out for a few hours yesterday. It was doing the same thing again. Anyone have any ideas what could be happening and what to look for?

At full speed it starts to loose power and make a bit of a jolting noise. It's hard to explain it but as the driver I can notice it while everyone else it the boat is oblivious to it. Any help is appreciated!

 

[Bt Doctur]

Re: 4.3l EFI Mercruiser high speed issues

hi-speed lean condition in #6 with detonation

 

[Don S]

Re: 4.3l EFI Mercruiser high speed issues

When was the last full tuneup and compression test?

 

[bluewaterboater]

Re: 4.3l EFI Mercruiser high speed issues

I bought the boat about 1.5 months ago and have not done a full tune up. I had the bottom of the outdrive taken off, checked and a new impeller installed. And just last week the oil changed and fuel filter changed.

 

[bluewaterboater]

Re: 4.3l EFI Mercruiser high speed issues

hi-speed lean condition in #6 with detonation

Is this difficult to check? and expensive to fix?

 

[bluewaterboater]

Re: 4.3l EFI Mercruiser high speed issues

I was reading another thread in the forum about a similar problem with a 1999 4.3l EFI and the outcome was a bad shift interrupter. Is it possible my problem is caused by the same?

 

[Bt Doctur]

Re: 4.3l EFI Mercruiser high speed issues

If you have the manual,check the spark plug section. has good examples of damaged plugs. running lean with or without detonation will leave the spark plugs blistered snow white. worst case is a hole melted thru a piston.

 

[bluewaterboater]

Re: 4.3l EFI Mercruiser high speed issues

Update on my engine: My mechanic changed the fuel filter, new plugs, compression check was good, new rotor and cap. The plugs were old as was the rotor and cap.

I took it out yesterday all afternoon and evening. It runs smoother and seems to have more pickup off the start. I am still having a bit of an issue though. At about 43mph and 4500 rpms if I put the hammer down further i can hear some popping sounds which i believe are backfires. I don't get the hesitation the same as I had before but its still not right. My tach after about 4800 goes completely wacky bouncing everywhere until i cut it back. I understand my WOT is probably 4800 but it still shouldnt do this. I also noticed a couple times when i nail the throttle down from the start it backfires a bit at high rpm just before i level out.

Any ideas? Injectors dirty??

 

[Tail_Gunner]

Re: 4.3l EFI Mercruiser high speed issues

Well it sound's like you have tuned up the engine to a point where its healthly. What your probably experiencing is the motor hitting your rev limiter..Its set at about 4950 when that happens it cuts off fuel for a nano second just as it should. Take a quick look at your prop size and gear ratio it should be simple to make a quick pik

 

[woody66912]

Re: 4.3l EFI Mercruiser high speed issues

Well it sound's like you have tuned up the engine to a point where its healthly. What your probably experiencing is the motor hitting your rev limiter..Its set at about 4950 when that happens it cuts off fuel for a nano second just as it should. Take a quick look at your prop size and gear ratio it should be simple to make a quick pik

Or a igntion module

Or engine is going into knock, due to bad plug wire.
Without messing around to much with your plug wires check for carbon tracks, it looks like black soot on the wires.

 

[bluewaterboater]

Re: 4.3l EFI Mercruiser high speed issues

thanks for all your help! I will have my mechanic check out a few of these items.

What is a little baffeling is that when I first got the boat I don't recall this happening, I have had it full out without a problem. So I don't think it would be the rev limiter although this is something I want to check into.

The wires are cheap enough that I should just replace them anyways so one more thing can be eliminated.

Thanks!

 

[bluewaterboater]

Re: 4.3l EFI Mercruiser high speed issues

As for prop size, I am running a 21p stainless steel Vengeance. The gear ratio I think is 1:82 and the engine is 4.3l EFI. I think the prop is the original with the boat.

 

[bluewaterboater]

Re: 4.3l EFI Mercruiser high speed issues

Between the advice given in this thread and my thread in the prop section I think I got my boat issues straightened away. On top of the tune up I changed my prop to a 14 x 23p and now I can run full out without any issues. Apparently I was hitting my rev limiter and that was causing most of my issues. I am still going to put new spark plug wires on and a new thermostat to complete the tuneup we started.

Thanks for the help!!