Inconsistent bogging/acceleration until it hit around 20mph - Mercruiser 5.7l

[minn_darren]

Hi, I have a video below but here is some history. Head gasket was replaced last winter. Put it in the water and it was fine prior to planing but then it was about 50% power at full throttle. Brought it in and they said that something got stuck in one of the cylinders. The cleared/cleaned it and put on a new head gasket again. Then, I brought it out again and now at it bogs on initial acceleration...until it planes or 20mph. Brought it in and they said that the timing was off. They "fixed" that and it's still doing it. I cleaned the carb with carb cleaner and it's still doing it. I suspect it's the fuel pump and I am going to replace it today or tomorrow but any other thoughts. In the video I put the throttle full speed at 2 seconds in and just left it. You'll see how it runs...not good...bogs.

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[alldodge]

You need a new mechanic
Don't see bogging being the fuel pump, the carb either has enough fuel or it doesn't. Checking fuel pressure can always be good to know, but I would suspect carb

Heads been removed twice so things could have gone wrong. Hope the head was checked for flatness prior to install, and assuming there was a valve job. Loosing something inside a cylinder maybe not a very good valve job

Should have used a new gasket each time

Check spark plug firing order

Hope they know how to adjust timing

What is your serial number?

 

[minn_darren]

You need a new mechanic
Don't see bogging being the fuel pump, the carb either has enough fuel or it doesn't. Checking fuel pressure can always be good to know, but I would suspect carb

Heads been removed twice so things could have gone wrong. Hope the head was checked for flatness prior to install, and assuming there was a valve job. Loosing something inside a cylinder maybe not a very good valve job

Should have used a new gasket each time

Check spark plug firing order

Hope they know how to adjust timing

What is your serial number?

Thanks for your response....the serial number = 0m085518. Do you think I should press about the flatness and valve job? I will check the order...based on the video, what is your gut?

 

[alldodge]

It never ran right since the head gasket was replaced. The other issues that keep coming I'm wondering just what the mechanics have "actually" done. All things listed while time consuming are not hard, and if done correctly there should be no issues running again.

Did the motor over heat which caused the original thought of replacing the head gasket ?

 

[Scott Danforth]

Do a compression test
Measure fuel pressure
Go thru the carb

 

[hugh g]

Throwing money at it such as a fuel pump is just that, throwing money at it until you hit on something. What did they mean "something got stuck inside a cylinder"? Sounds fishy to me. If that was the case how did that "something" not damage a pison or the cylinder bore?

 

[minn_darren]

It never ran right since the head gasket was replaced. The other issues that keep coming I'm wondering just what the mechanics have "actually" done. All things listed while time consuming are not hard, and if done correctly there should be no issues running again.

Did the motor over heat which caused the original thought of replacing the head gasket ?

Yes it was completely fine before the head gasket was replaced. Ever since it's been acting like this. Actually, after the head gasket the top end was bogged and the low end was fine. Then they found "something" in the cylinder and redid the head gasket while cleaning the object. After that I put it in the water and then the low end was bad (video). They said the timing was off and updated the timing and it's still bad.

 

[minn_darren]

Yes it was completely fine before the head gasket was replaced. Ever since it's been acting like this. Actually, after the head gasket the top end was bogged and the low end was fine. Then they found "something" in the cylinder and redid the head gasket while cleaning the object. After that I put it in the water and then the low end was bad (video). They said the timing was off and updated the timing and it's still bad.

It was not overheating ...I never saw the gauge show that before the gasket replacement. There was clicking noises which prompted the head gasket change

 

[minn_darren]

Throwing money at it such as a fuel pump is just that, throwing money at it until you hit on something. What did they mean "something got stuck inside a cylinder"? Sounds fishy to me. If that was the case how did that "something" not damage a pison or the cylinder bore?

Hugh G, I asked them that (was the piston and cylinder ok after) and they said yes.

 

[alldodge]

We're going to have to go at this like they messed everything up. A clicking could be lifters but this would not need a head gasket.

Get a lianer compression gage from a auto parts store. Disconnect the coil, open throttle to wide open and do a compression test

 

[minn_darren]

We're going to have to go at this like they messed everything up. A clicking could be lifters but this would not need a head gasket.

Get a lianer compression gage from a auto parts store. Disconnect the coil, open throttle to wide open and do a compression test

Alldodge, I am going to do what you suggested today or tomorrow. One other thing, they replaced the plugs and wires last year. Should they have checked the plug firing distance beforehand or does that not matter much? Also, you mentioned full throttle...so open up the throttle all the way, turn over the engine a few times when doing the compression test?

 

[alldodge]

If head was removed so was the distributor. Checking firing order should be done. Star at plug No 1 and the work clockwise to verify they are in the right order. Your No 1 on the dizzy may not be in same place as the pic



Disconnect coil wire from coil and pull the kill switch (man overboard)
Place throttle at WOT position

1. Remove first spark plug and attach compression gauge.
2. Crank motor over 3 to 5 times
3. Record plug number and pressure gauge reading
4. Remove gauge and reinstall plug and plug wire
5. Go to next plug and repeat steps until all cylinder pressures are recorded

You want a gauge that screws into the plug hole, not one that must be held in place. Also it needs a pressure release button so pressure is held until released

 

[minn_darren]

If head was removed so was the distributor. Checking firing order should be done. Star at plug No 1 and the work clockwise to verify they are in the right order. Your No 1 on the dizzy may not be in same place as the pic

View attachment 349328

Disconnect coil wire from coil and pull the kill switch (man overboard)
Place throttle at WOT position

1. Remove first spark plug and attach compression gauge.
2. Crank motor over 3 to 5 times
3. Record plug number and pressure gauge reading
4. Remove gauge and reinstall plug and plug wire
5. Go to next plug and repeat steps until all cylinder pressures are recorded

You want a gauge that screws into the plug hole, not one that must be held in place. Also it needs a pressure release button so pressure is held until released

I replaced the fuel pump and no change. I also checked the firing order and based on your diagram, it looks like the prop is on the left side of the diagram...is that right? If that is the case, then the firing order is completely wrong. However, if the prop is on the right side, it looks right. It's a chevy engine, not a ford so the firing order looks right if the prop is on the right. If I am looking at the engine from the back, facing the back of the boat, the #1 would be on the right, closest to me. Is this correct?

 

[alldodge]

The pic above is that of a chevy car/truck motor so its showing the fan. Orientation is from the distributor, and No 1 is port side closest to the bow

 

[minn_darren]

The pic above is that of a chevy car/truck motor so its showing the fan. Orientation is from the distributor, and No 1 is port side closest to the bow

thank you. It appears correct then. I am going to try the compression test next....what a pain this has been. I want to have my ducks in a row so I can go back to the mechanic who started this in the first place...

 

[Roadking57]

Noooooooooo!!!

Find a seaoned mechanic familiar with chevy 350's! Not a melenial either.

just the fact that the orig mech told you something in the cylinder is BOGUS.
It would have lodged into the piston or head and caused major damage!!!!

It sounds to me like you have a basic fuel/fire problem that a computer cannot diagnose. Have a good 'Ol boy check the basics for you.
save you alot of hassle

 

[minn_darren]

Hi All, the mechanic took another look, this time ON THE WATER and said it had something to do with the module and distributor timing mode stuck off. He said he then just set the timing to 3000 RPMs because it wouldn't go into timing mode. I took it out today and it did run well. Anything I should be concerned about based on what he did (or didn't do)? Thanks.

 

[Grub54891]

You need to find a good mechanic. I have had the module get stuck like that, in my car, couldn't get the timing right, and poor performance. At that point it must be replaced. As sated, find a mechanic who knows what they are doing. I personally work on mercruiser's, volvo's, deisel motors, and most outboards. In this trade, you have to know alot of different things, and doing this for over 30 years you learn alot. A newbie may know some stuff, but they must learn to ask questions from the ones that actually know what to do.

 

[alldodge]

Agree something is messed up and this guy doesn't know what he's doing.

 

[QBhoy]

Sure sounds like a carb issue to me. Is that a 4 barrel carb ? Sounds like the secondary are delayed or sticking ?