Does this seem right? Looking for advice

1956olds said:
Isnt there another thread going on here about a knocking noise that cant be fixed?
Click to expand...

Yep, that'd be me: http://clubsearay.com/forum/showthread.php?t=35143

Haven't had the $$ to try any solutions yet but am trying ignition stuff first. Could be fuel but we ran all day the day before my knocking started and it ran fine. Still looking for an opinion on what my auto guy said.:smt100

Eddie
 
Has the cylinder compression been checked? Its easy enough to check, and might give you more info.
 
Pull the plug wires one at a time (and reconnect them) to see if the knock goes away. A wrist pin or rod knock will lessen when that cylinder is not firing. I've also had carbon build-up create a knock that sounded like a rod knock. Using an engine flush that pours in through the carburetor fixed a noise that a mechanic thought would take a long block.
 
Do a compression test. If you have a wrist pin failure it will wear a groove in the cylinder wall and you will lose compression through it. You will also pick up fuel in the oil as gas runs between the piston rings and the grooved cylinder wall. Still I believe it's a fueling issue. I always go back to the last thing I did before the failure occured.
 
is this throttle body or port injection? it could be flooding a cylinder and trying to compress the raw fuel hence the nock be carefull if this is so you will quickly damage a rod .sitting while filling up could have empty'ed the fuel out of the line which would explain the prelonged cranking to repressure the fuel line . pull the plugs and crank the engine look for fuel soak plug make sure you disconnect coil or distributor wire so it doesn't get spark and cause a fire . good luck
 
Thanks for all of the advice.

I met with the service manager and the mechanic today. The meeting went well, I am taking my boat back tonight to finish out the season as a dock queen, and start chasing the problem myself. When I asked the mechanic why would it not knock in neutral or reverse when revved, but would in forward, he said it was a load issue. I then stated that it would be under load in reverse at high RPM (which I tried) and he said not enough load...

So I'm taking the boat back tonight, and will await their invoice. Once I have their invoice, I will look forward to having follow up discussions. I will be looking at the fuel issues and see what I learn.
Thanks!
 
UPDATE:

I brought the boat back to my slip this evening. I put in the prescribed amount of dry gas prior to leaving the repair facility. I could get the boat to almost 3000 RPM's before I could hear the sound, which is an improvement. I still have black smoke coming from the exhaust. In neutral, the engine sounds just perfect all the way to 4500 RPM. Under load, I can get to just about 3K, and then hear the sound. It does sound like detonation, almost sounds like it is coming from the exhaust.

This mechanic and the repair facility are done with my boat. I will have another mechanic check it out. I'm also going to fill the tanks with fresh gas, as I heard from someone the gas dock I took it to right before the issue has 3 yr old gas, and has been through two owners in the past two years. I really do suspect it is some kind of fuel issue. I'll keep you in the loop, but I can't believe my issue requires an engine replacement at this point. Thanks again for all of the advice!
 
One other question. If I am dealing with low octane fuel or dealing with water in the fuel, would that potentially cause the motor to run rich, dumping fuel out of the exhaust causing the black smoke? Would this cause detonation in the exhaust?
 
If you are dealing with phase separation, then yes, the fuel would be burning badly with a very low octane rating. I don't know about rich, but incomplete combustion would make it appear to be running rich. I'm still betting on bad fuel and phase separation. Dry gas isn't going to help much since the problem is because of alcohol in the fuel. Adding alcohol is replacing what was lost when the alcohol and water separated out of the gas. But that's about 10% of the total. You'd need to add something like 10 gallons of alcohol...
 
fc3 said:
If you are dealing with phase separation, then yes, the fuel would be burning badly with a very low octane rating. I don't know about rich, but incomplete combustion would make it appear to be running rich. I'm still betting on bad fuel and phase separation. Dry gas isn't going to help much since the problem is because of alcohol in the fuel. Adding alcohol is replacing what was lost when the alcohol and water separated out of the gas. But that's about 10% of the total. You'd need to add something like 10 gallons of alcohol...
Click to expand...

Yikes! Do you think filling up with (I'm probably at about 1/2 tanks) higher octane/fresh fuel would help? I'm betting on fuel as well, as I have heard horror stories (after I filled up of course) of this gas dock. It's not my normal spot to fuel up, but it was on the way to our destination.
 
Frank
What about octane boost stuff? Would that help?
 
Not a clue. I'm not a chemist or petroleum engineer. I just string together a bunch of things that I know, apply a little logically do-hickey along the lines of structural induction and try to solve problems.

I still think it's gas. BTW, what does your generator think of that fuel if you load it down with a big load? You know, turn on the stove, the air conditioning, the water heater, etc. lots and lots of power draw. Or just get your wife to blow dry her hair.

Best regards,
Frank
 
As soon as these winds die down, I'm going to fill up with fresh fuel and will report if it makes a difference. The more I think about it, the more I think I just have bad gas. And poor quality fuel. :)
 
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