I just finished a diff install and new seals for the tcase and trans. Relatively simple stuff with the front subframe out. I also re-gasketed the oil pan. Everything went smoothly during installation. Test ran the car for 15 minutes at idle to confirm no more leaks anywhere.

Upon driving it for the first time I would get a nasty sound upon load. Something around 2k rpm, very minor load. It sounded like the oil pump cavitating, or maybe the ACD pump cavitating. I focused on the ACD pump because that is connected to the tcase I worked on. bled it a ton, and its fine. Also when its engaged during the bleeding it sounds totally normal.

I can make the sound stationary, but need significantly higher rpms to do it, and they are finicky. I need to cross into 3k in bursts or pumps to force the sound. However if I rev to 5k and leave it there, nothing. If I rev it to 2k and leave it there nothing. Passing through 3k briskly and it sounds a bit like the valve train. However some of my car buddies don't think its coming from the head. They think lose something rattling violently. Others, think valve train. I have trippled checked every bolt we touched during the project, so I really can't see how its related to that. Just ironic timing of the problem. Nothing before like that, and then very clear issue after. I think its somehow related to onset of boost, because of the load.

Does anyone have any ideas on troubleshooting this and where to start? I am going to try and get a video with sound to post.

 

Here is a video,

Let me know what anyone's suggestions are to troubleshoot. The injector ticking is very prominent in the video with the iPhone mic. Many of you may think its the common injector ticking especially with this video, but its not. That, I had, and resolved, and was much different sound. The injectors are noisy and I have confirmed with stethoscope testing (putting one on the injectors).

1 - AC Compressor - BUT why only under some load condition or seemingly creating that when revving past 3k briskly while in neutral.
How to Test? remove surp belt.

2 - Lifter Tick - The noise may be in the head, but its not lifter tick. I had that, and resolved it completely with the diesel cleaning as per the FSM. Its was gone for a while before I started this project. BUT why does it not occur at idle?
How to Test?

3 - Rattling parts - I checked every bolt I worked on 3 times at least. Then checked all others anywhere. Nothing lose or rattling.

4 - BCS - I have a Gruppe-S unit and when I put my ear near it, and induce the noise it doesn't come from it
How to Test?

5 - PCV - Another post suggested this, but what am I looking for. Its there, but now what?
How to test?

6 - Head/Cam/Rockers/MIVEC - Is it head damage for some reason? But only at load RPMs? Something to do with MIVEC advance?
How to Test?

 

Check to see if the downpipe is rattling against the cross brace. Typically that sounds very metalllic at certain rpms.

I would have the car on jack stands and have some one replicate the noise while you inspect to hear where it is coming from

 

Thanks, yup I removed both cross bars as one of the first things I tried. Its already been a 4 day brain teaser. I've been under it while someone was revving it to reproduce and its not helping me isolate. I just doesn't sound like its from underneath. Its weaker down there a bit. When you stand over the engine you hear it best. When I put my stethoscope to the head however, you don't specifically hear that noise. You hear it bleeding through the ear pieces, but not through the tool directly.

 

How's oil pressure during all of this. You should video from under the good holding at a steady rpm where the sounds comes out and pinpoint from there. If its coming from the engine I wouldn't **** with it till u pull the pan off. I have heard that sound before. But it could be something else.

 

Oil pressure seems fine. When I crack the oil cap while idling there lots of splash feeding the top of the head. When I rev past 4k into 5k its totally quiet. I can't get the buzz/rattle/clank to come on up in that rpm. Only when I swing past 3k aggressively. Unless I am driving and then load will allow it at 1800rpm.

 

I did tests to eliminate some choices.

1 - Its not any accessory. I removed the surp belt and ran it, and I could do it exactly as before.

4 - Its not the BCS. I unplugged that and could repeat the noise exactly as before.



If its MIVEC, what do I look for when its not running? How do I prove that.

Calling Mivec Guru's....John......

 

I was trying to hear the sound you are investigating in your video...its hard to tell but is it a rattling sound? I couldn't pin point the sound but I think I heard it.....

Do you have a HFC installed or test pipe? I had a rattling sound from my HFC. The sound was from the material inside the HFC coming apart..... Probably not related but my HFC also touched up against the driveshaft from time to time. After figuring it out, I simply had to adjust the alignment a little and that took care of that sound for me....

I'm interested to see what this turns out to be!

GL!

 

Its hard to hear in the iPhone mic. In person its very pronounced especially in the cabin. I think the cabin filters out most of the engine noise, but that noise cuts through. Test pipe, and when laying under the car its very faint indicating the top in or around the head.

 

After re-reading this, it happened after the diff install and tranny seals etc.

I would expect something did not go back together correctly even if it went smoothly as you indicated....so ? clutch TOB ? input shaft bearing screwed up that causes knock but if bad enough maybe the metallic ringing as well ?

You indicated the ACD pump was tested and did not cause any of the noises. Lets that out. Also the downpipe is not likely as you removed the cross braces.

Was the downpipe the correct one that clears the ACD transfer case ? Is it touching the transfer case or oil pan at any place?

cant think of any more right now

 

The trans never moved off of the block, just the tcase off of the trans, so clutch or TOB etc were never touched, however we can still prove its not those, by the fact that the sound stays with engine RPM and not drivetrain rolling.

i.e. if it was a gear set issue in the trans we might hear it when in neutral and the input shaft is spinning the output shaft gear set, though none are engaged. From there the drivetrain is static. We have the noise, so we know its not anything after that. When I put the car in gear and get the sound by low load and low rpm, the car is barely moving. Just at take off the sound is with the 2k rpm, and not with the driveline.

When in neutral the clutch is fully engaged, and the sound is no different than when clutch is slipping for engage on takeoff.

Yup, DP doesn't touch anything. It has a bend in it. I also un and reinstalled it twice to make sure the donut ring wasn't pinched.

 

Resolved by removing the intake cam and cleaning out the passages with compressed air and cleaner. Still not sure of the cause but it seems that the last cleaning did the trick.