Bought this truck a few weeks ago knowing it had a quiet knock.
1997 F150 5.4L, automatic, 17x,xxx miles, always good oil pressure, currently running 5w20 amsoil w/ amsoil filter.
Truck runs/drives great. Going WOT or heavy throttle feels good and smooth.
Symptoms
Slight knock at cold idle, warm idle usually no knock.
-----With the truck at operating temperature---
More noticable in cab rather than listening under hood.
More noticable driving around in town (20mph and under) rather than on the highway.
Most noticable between idle and 1600 rpms.
Only audible under light throttle/accelaration. I cannont hear it under WOT or heavy throttle.
Noise also occurs just after letting foot off the gas. For example- Cruising 20 mph, rpms around 1500, let my foot off the gas to coast, and while the rpms decend the knock occurs, until rpms get back to idle speed.
The time between the knocks is roughly half a second at idle, slightly faster with higher rpms.
Previous owner said it was piston slap, and im just not "sold" on that yet.
The past hour iv been searching through posts with 5.4 and 4.6 knocking issues and came up with some possible "internet diagnoses" such as:
-Piston Slap
-Cracked flywheel/flexplate
-Rod bearing
-Timing chain tensioner(s)

I will do some more thorough testing when its nicer out. To try and pin point where the knock is coming from.
Sorry about the long read, but any ideas, input, past experiences, is greatly appreciated.
Thanks

 

Check out cam phasers on the search button. Alot of talk there about it, even a video from ford on the subject. Perhaps others will help you locate the video.

 

cam phasers were not on the 97 engines... the 5.4 piston skirts are coated with teflon to prevent wear on the pistons and piston walls when the material wears you will get a piston slap noise while cold ford considers this normal..

 

Did a little more searching used some different key words and found this thread. https://www.f150forum.com/f11/knocking-10070/

Things i gathered from it-
-Original poster has similiar miles, a knock, and for the most part the truck runs pretty good. He also had a rough idle situation, as do I, but my rough idle comes and goes. This does not happen all the time---- When the trucks idling the rpms will randomly dip down to 500 and the engine will run rough. I will give it some gas and bring the rpms up, and sometimes RPMs will stay normal 750ish and other times it will just dip back down to 500 rpms.
Original poster found he had one bad coil, he replaced it, and his truck is running and sounding alot better.
Really makes me wonder if I have a bad coil as well
- Good old bill posted: Very similiar to my situation. And original poster was told by the dealership his wrist pins were bad, but he fixed his issues with a coil.

What im getting at is maybe i just have one weak coil? Or wrist pin/piston slap.
Thoughts on this?
Thanks

 

i had the exact scenario with my 05 but with the 4.6 , tried 10w40 even and same thing ,never found out what it was cause i bought an 09 with the 5.4 and hoping for no engine noise<no noise as of yet...fingers crossed!>

 

Sounds just like the timing chain is slapping the front cover.

 

Im really itchin to get out there and pull off some plug wires one at a time, to see if the knock changes but its cold, windy, and snowing right now.

Can someone tell me, what it would mean if i pull a wire and the-
-Knock stays the same
-Knock goes away
-Knock worsens

 

just run it...and see if it gets worse...if it's piston slap it wont...even an out of round rod can go a long time before it gets worse...

 

Went and scanned the truck today for DTCs, it had cylinder 2 misfire, and a system lean code.
I had them cleared and im waiting to see if they come back. Because the previous owner swapped a bad coil out, but im thinking he maybe never cleared the code afterwards.

 

Maybe its in my head, maybe im just listening harder. But the knock/tap seems to be occuring more, its not getting louder, but im hearing it more frequently when driving to school in the morning (16 miles). But again, going WOT on the highway feels and sounds great.
It was a little colder today than it has been, would that have anything to do with it?