New to forum, but read often. It is a great place for diagnosing problems. I have a 99 F250 with V10 knock(170,000). I have isolated the knock to the back of engine front of transmission area. The knock starts very quietly and then gets louder and louder until it is very noticable inside and outside of vehicle. The knock gets louder and louder and then stops and starts over very quietly. Most of the time it doesnt get very loud before it stops and starts over. It reacts the same way at idle, under load, at higher rpms, don't matter. I have listened with a pipe and it is not coming from any one of the exhaust ports, heads, plugs, trans casing, or exhaust pipe. But it is definetly in the back of motor front of transmission. Not left or right side. It is there cold or hot but seems to advance louder and stop and start quiet when cold. It is always there either way, just not always as noticable inside. Has anyone had this problem? Any ideas would be greatly appriciated.

 

It could be a piston slap. Mine had a similar problem wich was a burned piston
Are you losing any coolant or excess oil consumption?

 

No more oil or coolant than the last 60,000

 

Does it run any differently? Or does run like it ALWAYS has, but just with the"knock"?

 

Runs the same as always. Motor runs great and has plenty of power. Just embarassing to stop at gas station cause the knock will sometime be there when I stop and other times not. And we all know how often I stop for fuel.

 

The way I explain the knock is it sounds like a loose bolt that is barely touching metal and as it slowly comes out it hits harder and harder then pops back in and starts all over again

 

Are automatic or manual? Maybe torque converter bolts? I have no idea because it doesn't make a whole of sense especially with it not affecting the engine.

You may need to get under instead of on top of it.

 

I have had torque converter and other bolts come loose over time that is a good place to check too! How is the transmission fluid level and it also could be a catallytic converter knock. I had a crown Vic with all of the above wrong with it.

 

Checked the torque converter bolts and they are tight. Havent checked the fluid. Checked the fluid a month ago and was full. But i will check today and find out. I have a pit and have been under it many times. I have even put my ear on the tranny bell housing and it isnt any louder. The problem is that when the knock is louder, I am not around the shop to drive it over the pit. When I have it over the pit, I have had it running for up to an hour waiting for it to get louder. I have left it cool down all dy and started it and the knock is very soft, then leave the shop with it and that afternnon I heard it get louder a couple times while driving. It has been a real pain in the A$$. It seems like it knows when it is pulling into the shop and quiets down. I have even pulled over the pit when it has been loud, got out, ran to get under the truck and it stopped and started knocking softly before I got there.

 

What kind of oil and filter are you running? I have a video of my noise I'll post after work. Has the truck ever ran low on coolant and has it been flushed? And do you know any of the service history on it?

 

Just following on the torque converter idea, you checked bolts but did you check to see if the flexplate is cracked?

 

torque converter inspection plate ???

sometiems they can make a noise but its usualy not described as a knock, more of a vibration..

still its worth getting under there with a screwdriver and pry it away from which ever side its rattling against if thats the issue..

 

Maybe valves or rocker arms loose? Did you listen for it near the valve covers?

 

Your on to something there, (a cracked flex plate Will Knock) and it is more prevelant at low rpm's. Have seen it on a dodge truck a few years back.

 

Is it a knock or a tick? Mine doesnt have a knock but it has a random tick that goes away after its driven for approx 15 min but i cant figure out where its from either.