this post is in relation to the motors that have a random knock near #3 or #4 cylinder, seems to happen to both 5.4 and 4.6 motors. (i drive a 4.6)

ok so after a couple days of lengthy searching i've come up with the following possibiltes. how do you narrow them down to a fix?

1. cat ceramics broken and rattiling around
2. bad plug wire/ random spark knock
3. A/C compressor bearings gone
4 random pully loose
5. belt tensioner loose
6. forgot to reinstall a bolt and its rolling around under the intake (ovbious fix)
7. Coil packs (or bad tower on a coil pack)
also if anyone has other reasons/ ideas i will add them to the list. seems alot of people have this issue.

 

I'd be interested in this topic also. My 5.4 makes the same sound. I'm hopping it's a pulley and not the cam phasers.

 

I don't think the 97-03 F-150's have cam phasers.

 

Ok, eliminate that.

Thanks!

 

Correct, only the 04+ have the cam phasers.

I will keep tabs on this post to see what the knock turns out to be. I do not have a knock at this time, but it will be good to have some ideas incase it does develop one.

 

updated with Coil pack info.

 

talked to a ford mechanic today about this, he is leaning towards exhaust rattle. either a loose hanger or the aforementioned converter issues.

 

It's almost funny the number of things we could guess. A buddy of mine over here was a Ford mechanic and says these engines have a valve tap. Nothing hurting anyhting, just a tap. I'm sure there'll be many more possibilities.

 

the idea is to list what we can come up with in one thread and figure out ways to narrow each one down so when someone has a problem they can use this thread as a tool to figure out their own "dreaded knock"

 

after a bout 2 hours of listening to my truck the other day i found my noise to be comming from the ac compressor and i possibly have a pulley making some noise as well. i can say its (in my case) an ac compressor issue. as the compressor cycles i hear the noise. Im going to change my drive belt thursday and see if the change in tensoin relieves the noise. my drive belt is pretty worn and needs changing anyways.

 

i changed the drive belt and it quited the sound down a slight bit. but it is definatley comming from the compressor. sound only appears when the clutch is not spinning. maybe some wd40 will fix this? or am i in for a new compressor?

 

My AC clutch destroyed itself and made an awful noise. You can replace clutch without replacing compressor and venting AC system. New clutch is very quiet. All parts available at autozone for 100 bucks. Lot cheaper than a compressor.