Rough running 496 Mag. White smoke. (Video attached)

Good morning, I am having basically a same issue.

Back in time, was that engine also making noise, knocking and some vibration? Basically as like you said, running rough?

Thank you.
 
highslice said:
Is it running rough under load? Or at idle? Does it miss or backfire under load?
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Doesn't hold idle speed and making knocking noise. Not easy to start it up without throttle and making a black smoke from the exhaust and flame arrestor too. Oil, water pressure are ok, temperature as well. New spark plugs just installed.

Water in the fuel? Fuel regulator? Cylinder pressure? I don't know yet.

Thank you guys.
 
An engine making a knocking sound and spewing black smoke is never a good sign. I believe we will be of better help once you get a mechanic to look at it.

A decent mechanic will do a compression test and diagnostics on the engine. Sure it could be really bad fuel but the other engine doesn't seem to be affected.

Was it running okay before you changed the plugs? If that is the case then plug wires might not be going to the correct plugs.
 
PlayDate said:
An engine making a knocking sound and spewing black smoke is never a good sign. I believe we will be of better help once you get a mechanic to look at it.

A decent mechanic will do a compression test and diagnostics on the engine. Sure it could be really bad fuel but the other engine doesn't seem to be affected.

Was it running okay before you changed the plugs? If that is the case then plug wires might not be going to the correct plugs.
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Engine was running like a butter 3 weeks ago. Since that time nothing changed. I replaced the spark plugs and was making sure about the ignition plugs. The other engine have it own gas tank. Thank you for any ideas.
 
Radek Kobliha said:
Engine was running like a butter 3 weeks ago. Since that time nothing changed. I replaced the spark plugs and was making sure about the ignition plugs. The other engine have it own gas tank. Thank you for any ideas.
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Milky oil is not a good sign - it typically represents water in the oil. Start by pulling plugs and looking for wet plugs or if water comes out. Water intrusion can come from many sources. Eliminate these first.

-Kevin
 
8.1's ignition wires are very short since each one connects to its separate coil near the plug - hard to get them mixed up. Did you use the right plugs? Seems odd that it was running fine before changing the plugs and that's all you've changed.
 
Jimmy Buoy said:
8.1's ignition wires are very short since each one connects to its separate coil near the plug - hard to get them mixed up. Did you use the right plugs? Seems odd that it was running fine before changing the plugs and that's all you've changed.
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Actually I replaced the plugs after the engine was already making the problems. I thought they were bad or wet.. didn't help
 

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I wouldn't be surprised if you were getting some water ingestion from one exhaust manifold (from the super white washed look of the plugs from one side of the engine. If enough water was causing the plugs to not fire the 8.1 system will compensate by increasing fuel to the working cylinders (might explain some of the other plugs being quite black and sooty). The bigger concern is the possibility of hydrolocking the engine while running which can really damage the engine. Connecting rods can bend or break since water cannot compress within the cylinders like air can. I'd be pulling the plugs, disconnecting 12v from both fuel pumps and turning the motor over to see if any water or water vapour shoots out of the spark plug holes. A bore scope might be useful before hitting the starter might even reveal some water sitting on top of pistons. Removing suspect exhaust manifolds will reveal rust on and around the exhaust valves if there's a breach within the exhaust. Raw water runs through these manifolds. They can look great on the outside and still have a breach of some sort inside, allowing the raw cooling water to leak into the exhaust area and drain down to the exhaust valve area. If a valve is open while the motor is off, water can drain directly into the cylinder.

I hope this is not the case and that it is a much simpler issue! Those plugs really look suspicious...
 
Time to pull the elbows and manifolds to get a better look at what ia going on. If wet my first instinct would be to inspect the manifold and elbows to see if they are failing.

-Kevin
 
Water get in there probably when I was flushing the engine with a fresh water..I put the mystery oil in the cylinders immediately and let it sit for like a week.. everything was just fine and engine was running like a butter till last week when the issue began..we found 4 cylinders are giving me around 180psi but the other side only 60psi on most of them..time to take engine out I guess or is there anything else what is worth to try? Thank you guys!
 
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