Exhaust Leak or Internal Knock? Video
 

1999 F150 New 5.4 ~350 miles on it. Longtube Pacesetter Headers with cometic mls gaskets. Stainless bolts.

It is making a knocking sound and I can't tell if it is internal or from the headers. I have a video that I hope you all can tell what is. I tried listening to the block with a yardstick, but I couldn't notice a significant increase in volume but my hearing isn't the best. I made sure all the header bolts were tight, but no change in sound.

That sounds more like loose a Torque Converter bolt. Does it ever smooth out or go very quite. Slowly bring up the rpm's from idle (700) to say 3,500, and see if it goes away then comes back. This tends to lead to a harmonics issue, like a loose TC bolt or something like that. Good luck.

Revving up from 700 to 3500 it was hard for me to tell, but it sounded like the knock got worse and then a little better at the end. The exhaust began to overshadow it. I took off the flywheel view plate and everything looks good and feels tight. The knock is very loud when under the truck. I have two more videos one from 700-3500 in cab and one from underneath viewing the tc and flex plate.

Man Austin J., that second one sounds bad. You need to get that checked out. That is a definite sharp knock going on. Who rebuilt the engine? I would be showing them the video, and looking for some guidance from them on what to do. Good luck.

P.S. The first video hints at the knock being there throughout the RPM range. This, to me anyway, is a sign of a possible rod knock or main bearing failure on the crankshaft. Have you drained your oil to see if there is any metal in the pan? Also cut open your oil filter and inspect it. If there is visible metal shavings in either pan or filter, you are looking at a rebuild in my opinion :'(.

I haven't drained the oil yet but the oil on the stick is still perfectly clean like it just came out of the bottle. I was looking more into the flex plate and torque converter sounds and it seems to match it more. I got a stethoscope and it seemed the knock was louder on the bell housing than the block. Tomorrow morning I am taking it down the road to a real good transmission shop to see if he thinks it could be anything other than internal to the motor. If it is the motor I have to ship it back to S and J engines in Washington for warranty work. I really hope it is the flex plate or torque converter with 155000 miles on it and not the new engine.

With transmission out it still knocks. It has to be pulled again and sent back to SandJ. I definitely wanted to have to do this again...

Sorry to hear that AustinJ, that s u c k s. Good luck on getting a good outcome with the engine builders. I just went through the same type issue, but with the transmission in my son's F150.

P.S. I would still pull the filter and cut it open to see what is inside.......unless the builders require it to be on the engine, or shipped separately to them for inspection.