Dom99GT

I have a knock on one of my cylinders i believe its a connecting rod because when i pull the spark plug and injector on that cylinder the noise disappears, i was wondering if i left the spark plug and injector off of and just ran on 7 cylinders until im able to pull the motor out if it would do any additional harm, i have another motor so im not to concerned but still just curious

Arrickh

I believe you would end up with a lot of fuel in your cats (if you have them at least!) which might be bad because they get hot.. Also it could cause balance issues with the engine so it'd shake a lot. Then again I don't know THAT much about cars so I'd wait on some other replys to see.

BlindGUYnAR

The rotating assembly on that cylinder is moving regardless of the spark plug or injector is plugged in or not.

If it was a mechanical noise the noise wouldn't go away by unplugging those in my opinion.

Look for an exhaust leak.

Dom99GT

Ok I was thinking that maybe with the cylinder off it wouldnt be firing as hard on that cylinder thats why i thought it would be the connecting rod, the sound is very confusing and id hate to pull the motor and find out it wasnt mechanical, the sound is the same as the videos ive looked up for bad rod bearings, but like i said, if i disconnect the plug and injector on the #7 cylinder the noise is completely gone, so should i be looking at the headers than for a leak? and if so why would it make a knocking noise like that? i had the oil changed and ran a light weight oil system cleaner through and it came back with no shavings so thats why i was leaning towards a connecting rod rather than the rod bearing

Chromeshadow

The connecting rod cannot make noise by itself, I have heard of times when the pin that connects it to the piston is loose, or the rings and cylinder wear to the point that the piston slaps the cylinder wall on the compression stroke. I'd definitely look for an exhaust leak first. If you have problems with rings you'll see a big drop in compression in that cylinder.
There are a bunch of things that could happen if you deactivate the dead piston, most of them are bad, real bad. Overheating, having whatever is worn totally break off, engine codes, rough idle, just to name a few.

WhiteFoxGT

if the knock goes away when you kill the cylinder its probably a worn pin. I've seen it a few times on the 4.6. Running it on 7 is useless... either fix it or dont run it

Dom99GT

Thanks for all the help guys ill look into the exhaust leak idea, if it turns out thats not it then i guess im pulling the motor for a new pin

BlindGUYnAR

Please return and let us know what you find it might be a pin, but for sure if you have headers look for a blown gasket or broken/cracked weld. Since you know which cylinder it is that will make the inspection easier.

You can feel around with a set of thick groves and the cylinder firing listening for sounds changes. Be sure to really check around the welds and the header flange.

If you hear absolutely any sound change you likely found a leak. You can also visually inspect for carbon deposits sprays especially around the header flange.

Again let us know what you find and good luck.

Dom99GT

So I haven't had a chance to check the headers yet I'm going to be doing that shortly, but an update on the symptoms, the Noise only occurs 2k+ Rpms, I can't hear it in 4th or 5 th gear but can hear it in every other gear in cluding neutral, maybe the road noise is to much in 4th or 5 th not really sure, the noise also only happens when I'm on the gas, if I'm above 2k and tap the gas or hold it steady I can hear the knock, if I let off the gas there is no knock at all as the rpm falls thorough the hole range, I can rev it up to 5k then let off the gas and as the Rpms naturally fall there's no knock, don't know if this changes any opinions on what the cause maybe, but thought I would share just incase

WhiteFoxGT

9/10 times, its the bottom end