Ford Truck Enthusiasts Forums - Mystery metallic knocking noise across rpm range

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Mystery metallic knocking noise across rpm range

I have a 2004 4x4 with a 5.4 liter. It recently started making a rhythmic sound like two pieces of metal hitting each other. The sound is more of a smack or knock with no resonation or ringing afterwards. The sound occurs at half the engine speed leading me to think it was in the valve train. I went ahead and replaced all of the rocker arms, hydraulic lash adjusters and cam phasers. I started it up after reassembly and it started just fine it purred for about two minutes of idling and then the noise was back. It would fade in and out sometimes pretty loud other times non existent. I took it for a lap around the block and noticed that I couldn’t hear it while accelerating but as soon as I let off the throttle you could hear it loud and clear I have an auxiliary oil pressure gauge and notice little to no fluctuation between when the noise was there and not there based on the gauge the pressure was about 40psi at idle and 70ish psi under load after the short drive the noise was basically constant. Thought it could be the spark plugs backing off but based on the ones I broke taking out that wasn’t the issue and I didn’t see any sign of blow by on the COP boots. Thought since it was intermittent it might be the AC compressor but I disconnected the clutch fuse and it was still occurring. Any ideas? And all help is greatly appreciated!

I couldn’t hear it while accelerating but as soon as I let off the throttle you could hear it loud and clear I

Motor idle has high vacuum and low oil pressure... Motor under acceleration has LOW vacuum and oil pressure depending on motor RPM.... motor under acceleration and high RPM has LOW vacuum and HIGH oil pressure. Possibly wheel end 4 x 4 engagement pistons (IWE system)..?. with LOW vacuum, they try to engage the 4 x 4. ........... or sounds like it is PHASER / cam chain related as it gets worse with low motor RPM and after warming up oil ( lower psi)

engage the 4 x 4 system on a gravel or dirt road and retest... Does the noise still occur when 4 x 4 is engaged ? If so, its probably not the IWE vacuum system.......I don't think it should be the IWE since you have the noise at IDLE which should be HI VACUUM... just opposite of the normal IWE problems.

My guess, based on my own experience, is (at least one) blown tensioner seal, probably broken chain guide - causing chain to slap inside of front cover. Mine was intermittent.

I have an 06 4.6 2v engine that ive been chasing what I believe is a knocking noise coming from the heads. The noise really don't sound like it is a rod or crank knock. I found my stock oil pump with erratic readings - I replaced the pump with a new melling pump. Then had real good oil pressure @ 75 psi @ idle and 100 psi when I goosed the throttle. Then found that I keep loosing oil supply to the heads - both heads - now trying to chase this cause down. What ever is blocking the oil to the heads is causing my knocking.
Here is a link to the same exact noise I'm hearing - and on my F150, it is not an exhaust leak:

The noise in the Mustang sounds like valve train noise. I don't know exactly what engine that is or if it has the variable timing set-up. Your V6 doesn't have any of that, being a pushrod engine with iron block and heads. If your noise sounds similar, you may have reduced oil flow to the rocker arm area under the valve covers. This could be from sludge build up, blocked oil pick-up screen or dented oil pan, bad oil pump (probably not in your case).
BTW, how did you determine that the heads were not getting proper oil delivery? Did you pull the rocker covers?
If you have a heavy sludge/carbon build-up visible under the rocker covers you probably have a sludge problem in the engine. I can recommend an engine cleaner but its so strong that black crud will run out of every gasket and seal if used at the recommended strength- but it does work. I had a lightly-used 350 in an old GMC van that would get sticky valves. I used a light dose of Kano 'Kreen' and it took care of it. The lighter dose usually will not cause oil leaks but this stuff dissolves baked-on crud.