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Mystery metallic knocking noise across rpm range

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Old 04-16-2018, 03:00 PM
M_C_shady
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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 couldnít 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 wasnít the issue and I didnít 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!
 
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Old 04-16-2018, 09:30 PM
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I couldnít 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)
 
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Old 04-16-2018, 09:36 PM
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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.
 
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