Mercruiser 5.7L Engine Knock - when accelerating - incident likely caused this

[minn_darren]

Hello, I have a 2002 Chapparal deckboat with a Mercruiser 5.7L engine. I have had it for 4 years and keep it very well maintained. It has been completely fine (and actually great!) up until now. The ticking happens once I get the RPMs up over 2k. There is NO ticking when it's idle or if I rev it in neutral. Also, the knocking happens often but it's not a consistent knock. Like I said, there was an INCIDENT. I was getting ready to pull a water skier and the depth finder said 7ft. Stupidly I ignored the low depth and tried pulling him anyway. He ended up falling right away but as I went back to get him I saw a trail that I created from the bottom of the lake. Also, when I was trying to get him up i could tell the boat was struggling, but I didn't realize I was likely hitting bottom until after. I didn't hear the noice so I tried getting him up again and then I heard it once the RPMs got up there. I stopped immediately and kept it at low speeds and brought it back to the dock. I took it out again today to see if it magically cleared and it's the same issue. I am not that mechanical but I checked the oil dipstick to see if there was any bubbling or cream color and it looks just fine. I don't want to get completely screwed by a mechanic so if you have ideas of what happened, that would be helpful so I can direct a mechanic, without having them completely screw me. Any ideas and suggestions on what happened? Thank you!

Let me know if you can't see the video. The knocking starts when I rev it higher towards the end of the video:
https://photos.app.goo.gl/VThsRE5z7q8sA1tDA

 

[Rick Stephens]

Draggin the bottom isn't going to do anything to your motor. Not unless you hammered it. Your video shows as just a photo for me. So can't really help based on that.

Personally, I'd pull the drive and plug a hose into the water port on the bellhousing and see if the noise goes away.

Ric

 

[minn_darren]

Thanks Rick. From what I am seeing, people are saying it could be a blown head gasket or possibly a blown coupler? Do either of those sound like a possibility or would you rule either of them out given the incident that likely caused this?

 

[Rick Stephens]

Thanks Rick. From what I am seeing, people are saying it could be a blown head gasket or possibly a blown coupler? Do either of those sound like a possibility or would you rule either of them out given the incident that likely caused this?

Unless you overheated it, you probably don't have a blown head gasket. And if you can get power to the prop, you don't have a blown coupler - which acts just like losing a clutch in a car. You haven't given me anything to state an opinion on why you would hear a ticking.

 

[minn_darren]

Try this link to see/hear the video https://photos.google.com/share/AF1...?key=dVRTa04xdjdNMGxTX3BGbWl5Y0hLNF81cWF5RExB

Also, the symptoms sound similar to this forum https://forums.iboats.com/forum/eng...nging-sound-under-load-5-7l-250-hp-mercruiser

Let me know if you see the video and what other questions you have that I can answer to help get to the root of this.

 

[Searay205]

Not a blown head gasket, not a coupler. Almost sounds like exhaust dampers or an shell or rock stuck in exhaust bouncing around.

I take that back sounds like predestination. Put some 93 octane in it. You may gotten bad gas.

Who knows. very random noise, either rock in exhaust or pinging. start up on hose and see if you can duplicate if you can't its not predentination as there is no load.

 

[minn_darren]

Searay, given the incident that happened, I don't think it's the gas...granted I did put in 5 gallons when we started that day but it was running just fine prior to the water skiing / bottom out issue. When you say "start up on hose", do you mean take it out of the water and connect the earmuffs?

 

[Searay205]

Yes, on muffs. get a mechanics stethascope and while its making the noise listen around you exhaust manifolds. If you pumped mud, dirt etc through it may just be a rock or shell bouncing around. It should dislodge itself eventually, hit some rough waves

 

[minn_darren]

Draggin the bottom isn't going to do anything to your motor. Not unless you hammered it. Your video shows as just a photo for me. So can't really help based on that.

Personally, I'd pull the drive and plug a hose into the water port on the bellhousing and see if the noise goes away.

Ric

Hi Rick, wondering if you meant hook it up to the earmuff too? If I do that and the noise goes away, what does that tell me/

 

[Searay205]

You have pre-ignition. its pinging. Try some 93 octane as a test. It don't ping on the flush ears since there isn't a load.

 

[Rick Stephens]

Hi Rick, wondering if you meant hook it up to the earmuff too? If I do that and the noise goes away, what does that tell me/

What I was proposing was removing the drive altogether and sticking a cutoff garden hose into the water passage to provide cooling water and testing the motor without the banged up drive attached.

As noted, if the problem is detonation, that is from running lean or having the timing way out of whack. Neither of which would be caused by smacking the bottom with the drive. I was just proposing a way to test the motor without the drive in the equation. Takes 10 minutes to pull the drive. Shoving a hose in isn't exactly needed just to listen for a couple minutes. Don't even need cooling water for that without the drive attached. Please note, if the drive is attached you must have the muffs on or you will burn up the impeller. Running for a couple minutes sans drive and without water at all is not going to do a thing bad since you won't be getting hot.

 

[chs marine service]

sounds like you have a lean fuel condition, causin detonation (pinging) hook up a fuel pressure gauge and rev it again. do not continue to drive it, i had a client with a new engine, 10hrs old who had a bad fuel pump cutting out on him at high rpms and blew the motor due to detonation. although his engine was fuel injected which requires higher fuel pressure.

 

[minn_darren]

Can someone tell me if my 2002 Mercruiser 5.7L 250 is carb or fuel injected?

 

[H20Rat]

You most likely didn't touch bottom. 7 feet is more than enough, what you were seeing the prop blast aimed down at the mud and stirring it up. I routinely pull skiers up with 4 feet under the sender and don't touch bottom, but it certainly stirs it up.

 

[Lou C]

definitely sounds like pinging I'd consider pulling the spark plugs and looking at the center electrode insulator, if its blistered white then that suggests a lean fuel condition that merits further investigation, if the center electrode insulator is light tan/brown/grey then its not as likely lean fuel mix but bad gas, low octane gas.
I'd also dump out the fuel filter into a mason jar and see what it looks like .

 

[nola mike]

What I was proposing was removing the drive altogether and sticking a cutoff garden hose into the water passage to provide cooling water and testing the motor without the banged up drive attached.

As noted, if the problem is detonation, that is from running lean or having the timing way out of whack. Neither of which would be caused by smacking the bottom with the drive. I was just proposing a way to test the motor without the drive in the equation. Takes 10 minutes to pull the drive. Shoving a hose in isn't exactly needed just to listen for a couple minutes. Don't even need cooling water for that without the drive attached. Please note, if the drive is attached you must have the muffs on or you will burn up the impeller. Running for a couple minutes sans drive and without water at all is not going to do a thing bad since you won't be getting hot.

Your flappers and exhaust pipes will still get hot

 

[minn_darren]

Hi Lou, I am seeing from some other posts that it might be as simple as cleaning with intake valve cleaner? I am not sure if this engine is fuel injected or carb...I am not at the boat ...it's on the lake. It's a mercruiser 5.7l from 2002. Here is the picture of the serial numbers. I will definitely check the plugs too.

 

[Searay205]

Seriously, cleaning with intake valve cleaner? No that will not solve the problem. As has been said you have bad gas or are running lean. I lean toward bad gas unless the pinging has been getting gradually worse over months. It sounds like you never heard this sound before so what ever is the cause was a recent change such as fuel. Pull a couple plugs if you want i would just put 93 octane into it. Not octane booster (no shortcuts will work) 93 octane gasoline.

 

[Lou C]

Problem is you are doing a lot of guessing but without enough diagnostic work. A lean fuel condition also cause this, looking at the plugs can tell you that. So can a rich condition because it can cause carbon deposits which can raise compression to the point where you get pre ignition. For that problem intake valve cleaner wound actually make sense. Years ago we had a ‘70 Ford Torino with a 5 liter 2bbl. The choke was very slow to open and it pinged like crazy. I fixed the choke problem but to get rid of the pinging I had to run 2 cans of top engine cleaner through it. The carbon that blew out looked like dirt coming out of the tailpipe. After that it ran on regular gas no pinging. But you don’t know what’s causing it in this case. At least look at the plugs and do a compression test. I read somewhere that if the engi e has an knock sensor and it fails this can happen. Might be worth looking into....

 

[Scott Danforth]

Hi Lou, I am seeing from some other posts that it might be as simple as cleaning with intake valve cleaner? I am not sure if this engine is fuel injected or carb...I am not at the boat ...it's on the lake. It's a mercruiser 5.7l from 2002. Here is the picture of the serial numbers. I will definitely check the plugs too.

If you cant tell the difference between a carb or EFI.....slowly back away from the tools