Hello fellow diesel members. I need some advice as to whether this sound is normal or not. Here is the background;

In december, the 3" exhaust was done up and I hollowed out the airbox a bit (snorkel gone etc.). The turbo would make a low frequency whine around 1700 rpm only when the engine was still cool and under light acceleration, and would make a constant medium pitch whine at 2000-2200 rpm with medium acceleration. It was quite pleasant. You could even hear the high-pitch kenworth truck kind of whistle when alongside a building or fence with the windows down when letting off the pedal from strong acceleration. Well, that all changed yesterday.

Yesterday, I had some gauges installed on the pillar--boost and pyro. I worked alongside the mechanic as I was not totally sure how to do this on my own, but now I do after watching. So, we got down to taking off the upper air intake (s-engine). This is what I believe it to look like, and what we saw in it:
http://www.thefilebucket.com/userfiles/Silvy/Upper%20Air%20Intake.JPG

So, we ran it through the parts cleaner....twice and got most of the oily-solid out. We then drilled the hole in the intake for the boost line (put it upper right corner of the intake on my drawing) and bolted everything back down with a new seal between the upper intake shown above and the lower piece it bolts onto. We then tapped the EGT probe, ran it all inside, hooked up the electrical and away I went. Oh, and there was an electrical plug (3-prong in a row) that plugged into the underside of a small black plastic box right on the elbow on the intake shown above. The bracket that locked this plug in place broke so we duct-taped it in.

I get out on the road and as the new boost needle climbed to 3 psi, a new noise started. The thing started to scream like a banshee!!! I drove to a nearby fuel station and popped the hood with it running. All seems okay but I still couldn't (and still can't) believe this screeching howl. The turbo seems to operate right--boost runs 3-6 psi on medium acceleration and will spike to 9 if I get on the pedal but falls back quickly as we all know. Here is a couple sound clips I got this morning. Sorry about the background noise (my recorder doesn't seem to like this engine). I got a free upload space account to make this work so hopefully it works for a while. Tonight i'll get a better sound clip.

File #1 (better one):
http://www.thefilebucket.com/userfiles/Silvy/%20Turbo%203.MP3?PHPSESSID=dd018a95248bc8120e4cf64 b5c600af5

File #2:
http://www.thefilebucket.com/userfiles/Silvy/%20Turbo%201.MP3?PHPSESSID=dd018a95248bc8120e4cf64 b5c600af5

Thanks for any input, it is much appreciated. Let me know if the link doesn't work.

that sound clip sounds ok i guess... i do remember my 6.5td when i had her would sound similar to that when i had the air box lid off [canister type filter held on with hose clamp]

looks like an egr intake manifold... disable the egr system if that is what is there asap... easiest way is to take a BB or screw and shove it in the vacuum line and don't worry about it.. egr on these engines is always NFG [if it is working or not, soon enough it will be in the not working class]

Thanks for your tips. Yes it is an EGR intake set up. I take it the EGR unit (is it a valve or what?) is the thing that looks like a wide metal teapot with holes in it that mounts on top of the intake I drew. It has a little black line that plugs into the top of it: is this the line i'm supposed to plug with a screw? Will it then stop making a damn mess of the intake? Thanks again.

Silvy go to my website link in my sig and check out a modded L56 upper, something that needs to be done to any L56 IMO, also are you in a smog check location, several things you can do for more oomph to wake up that L56 most is in the FAQs what can I do for more power thread. Yes the EGR is dead center on upper intake; one thing I prefer to do with EGR bypass is shim between EGR valve and intake, that way you are mechanically blocked from flowing any gasses, if the EGR spring is weak, vac is use to open the valve, on later model OBDIIs vac supplied to EGR is monitored by firewall baro, PCM is a little smarter than OBDI and will throw a code if you just plug the vac supply line.

The shim allows for blocking of EGR but vac system still actuates so a code isn't thrown, also easily removed when you resume on road driving, as what I propose is for off-road use only ;) . Also don't forget to replace donut seal between upper & lower intakes, it's a 1 time use gasket/seal, it will allow flow of gasses. Ultimate solution if they don't verify OEM configuration by VIN where you are is to swap out to a L65 intake system then no EGR is flowing in the intake.

MAke sure the turbo shaft doesn't have excessive play that would allow it to grind away at the housing, seen (heard) that one before.

Thanks for your reply Turbine Doc, I'll go on over and check out your website on that. To check for play in the turbo shaft qm, do you just disconnect the hose coming from the airbox to the turbo and grab hold of one of the blades and try to wiggle it?

Any theory on why that much sound was never there before but now it is?? It actually sounds quite a bit louder than in the first audio clip, the engine rumble takes away from it on the recorder.

Yes just wiggle the thread and bolt of the turnine endshaft. If the wheel can touch the aluminum housing the play is excessive.

Suspect an air leak - really loud under Boost............

Yes gmctd, it does seem quite excessive and kicks in after about 3 psi. I think a good approximation is if you were to crank the interior fans on and the radio so it almost drowns out the engine rumble you would still hear this strange sound over it all. Where could it be possible to have an air leak? Thanks.

edit:
I just finished testing the play in the turbo shaft. There is no movement in the shaft, its rock solid in place and spins freely. I did however notice that the clamp holding the hose from the filter box directly onto the turbo inlet was completely loose. Aha I thought to myself; this could be what gmctd was talking about. I tightened that sucker down and went for a test drive.

Well Censored !! Still there! Could a leak be farther down the intake path. Could it be that the upper intake was not bolted down tight enough onto the (new) gasket? Could it be the egr itself--keeping in mind that the air paths for it were cleared of gunk--could it be whining away? :help2:

The leak is something that was overlooked when the upper plenum was replaced - I'd recheck the gaskets and bolt sealing and\or gage-tap installation process.

Maybe missing o-ring in MAP sensor, IAT sensor loose\cracked, etc.

check both hose clamps between the turbo and the upper intake, the hose maybe rolled under or clampst left loose.

Thanks TDG and gmctd! I did check and double check the dual hose clamps on the tubing from the turbo to upper intake--both are good and tight. gmctd, please enlighten me on where and what the MAP sensor and IAT sensor are (always wondered what those 2 things were--i'm still learning, sorry) . The gasket between the upper and lower intakes was replaced and the 4 bolts tighted down quite a bit. So, the possiblility lies on the MAP or IAT sensors i guess. Thanks again.

IAT sensor is 3/4" brass, MAP is black square thing that you had to duct tape.

You did replace the mystery gasket (http://www.kennedydiesel.com/airboxmods.html) right? (see bottom of page)
And the grayish, graphite looking one that goes under the EGR boss?

Isnt there 6 bolts in the upper plenim?

The gasket between the upper and lower intakes was replaced and the 4 bolts tighted down quite a bit.Ahh, I didn't even catch that before. I assume your referring to the bolts on the 4 corners of the uppper intake, what happened to the 2 in the middle that hold your EGR down???

Sorry TDG, yes the two in the middle holding down the egr were re-tightened up with the graphite-looking seal inbetween the egr valve and upper intake. The seal between the upper and lower intake was replaced and those 4 corner bolts tightened down (6 bolts total tightened down). The 3/4" brass fitting (IAT) is plugged into the intake with threads sealed with an orange paste.

The only possibility is that the "mystery gasket" may have been overlooked. Thanks for bringing that to my attention. It may have been stuck to the upper intake when it was pulled off and went into the parts wash by accident and got lost. It won't be such a mystery if that fixes the problem. It could then be called the....."keep your truck from screaming like a possessed banshee gasket" ):h But seriously, could that thing missing make a really loud screaming whine? I'll go and check it today and get one in there if missing though.

My friend and I were pondering over this for an hour yesterday. He figures theres a gasket either missing or not seated properly. Is it possible that if the line used to carry the boost pressure to the gauge had a small leak from a pinch would it be loud enough to overpower the engine, fans, radio? I really doubt it.

Last possibility is that where the flat nut was welded onto the hole cut in the cross-over pipe for egt probe to screw into, could it be that it was not welded enough around the nut and thus seeping air such that it blows like a whistle? Any ideas?

did you replace the centre gaskit that seals the upper plenum to the lower one where the exhaust comes up through the centre to get to the egr the round gaskit about 2" in diameter if you replaced the outer one and not the inner one the outer one may be a bit thicker than the original and now boost is leaking into the exhaust passage of the intake.

I think you are referring to the same 'mystery gasket' 69.

ahh yes i missed that post tdg

Well 69camarox, not quite. I went on down to the dealership planning to take apart the intake....again...knowing that I would need new gaskets. Turns out they don't call it a "mystery gasket" for nothing--as i sort of suspected even before I went in there. Of course, it doesn't show up on their computer system. So I said "just give me gasket to go between upper and lower intakes"--to the tune of $17.00 (sheesh). They did take my VIN and the lady there will call GM on monday and try to find out if they can get one.

So over to my buddies place to rip this apart again. Took the intake apart and inspected. Luckily, the "mystery gasket" was still sitting there (its hard to tell its there in all the crap but if you stick your finger down the center pipe you can feel the lip on it).

We determined that the new boost tubing was not the culprit (as I suspected) since we took it off at the intake and while I revved the engine in drive with the park brake on, he covered the hole where the boost line plugs in but the scream still went on. By the way, the engine only revs to about 1700 rpm even though the pedal is part way down (must be a sensor somewhere limiting the rpm when truck isn't moving)

Here's the interesting part. Keep in mind that the seal in there between upper and lower intake when we started today was only 3 days old. We found the seal to be broken in two places (oily crap had gone over the top of the gasket and sprayed outside the intake alltogether from pressure). We figured this was causing the screeching sound. I also didn't mention earlier that you could hear 2 tones of screeching (2 very slightly different pitches). Since the gasket was seeping in two places--hence, the 2 different pitches.

We then very very meticulously cleaned off the not-so-old seal (gummed on already in some places) with carb cleaner and carefully cleaned the upper and lower intake surfaces and tried to get any spec of anything off of there. As for the old mystery gasket, we cleaned it up as best we could and got it as smooth as possible. Spent probably an hour just cleaning parts. Placed in the brand new gasket, bolted down the intake and EGR valve and plugged in the IAT and MAP sensors.

The worst thing that could happen is the gasket blows apart again and starts seeping. I idled it for 10 minutes and drove it home like an old granny with absolutely almost no boost (6-7 min drive) and parked it on the driveway--been there for just over an hour now. I have no idea if the problem has been solved--didn't want to force it on the way home. I have my fingers crossed.

Dude Silvy, NAPA has the 'mystery gasket' for $1.99. They usually don't carry this item but can order it if you live near one. If not, they can drop ship it to your door. You'll have to pay shipping and handling this way, but it will be cheaper than your quoted $17.00. And besides you'll probably be going around in circles with the dealership for a 2 dollar part. NAPA part number is CRB225203.

Thanks a lot<SCRIPT type=text/javascript> vbmenu_register("postmenu_554779", true); </SCRIPT> jmkglloyd ! I was at NAPA near my place with the upper intake in my hands and the picture of the gasket that Mr. Kennedy has on his site but the fellow there had no idea what it was. The $17 gasket was the one that seals the upper and lower intakes. We will see if the work I did yesterday solved the problem, I have my fingers crossed. Thanks to your part # I may be able to find one of those gaskets now should this thing let go again.

Into a bit more detail on that seal leak. When the upper intake was off and you looked at the bottom of it where the round pipe comes up for the EGR, there was evidence of a pretty good leak going on there (oil blown away in all directions from where the gasket should seal). Is it possible that the EGR valve is not opening thus building too much pressure around the new seal? I figure this blow-out was contributing to the leaking of the new gasket that seals the upper and lower intakes. Any thoughts? Has this not happened to anyone before? The simple removal and replacement of the upper intake should not cause so much grief otherwise wouldn't this issue occur more often?

You can check the EGR function. Engine idleing, pull the line to the baro and put you finger over it and check for vac pressure. A moment later pull it away and you should hear the EGr clicking closed.

Were it my truck, I would just replace the lower manifold gaskets and block off the exhaust flow to the intake and forget about EGR leaks.

As for the mystery gasket, I would imagine a fuel shop will give you one. I know we have several lying around, they come in the install kits and don't get used for the HDs.

Don't throw em out! I'm sure many would appreciate the freebie, hell send em all to me collect and i'll pass em out to whoever wants one.

Oh I do keep them, and give them out freely ;) I'm sure other shops must do the same thing.
The engine only revs to about 1700 rpm even though the pedal is part way down (must be a sensor somewhere limiting the rpm when truck isn't moving)
I idled it for 10 minutes and drove it home like an old granny with absolutely almost no boost (6-7 min drive) and parked it on the drivewayAre you saying that you can't rev the engine past 1700????? Sitting still you should easily be able to punch that baby to redline! Are you getting smoke? Have you rechecked all of your vacuum lines? This doesn't sounds good.

It will go higher than 1700 if you take your foot off the brake. I was simulating a boosted launch as if I were about to race someone to get the turbo to kick out some boost pressure. It won't pressure if you leave it in park right (no load). This is just when sitting still with other foot on the brake into the floor to keep it from moving.

qm, is the baro sensor what the black line plugs into on the top of the EGR? Just unplug it there right, and do the test? Thanks.

Thats just a vacuum line to operate the EGR valve. The Baro sensor is on the firewall, driver's side, looks identical to the MAP and has a Green 3 wire plug and a vacuum line that should be tee'd off the line going to the EGR valve.

How much boost did you get floored, in gear with the brake on?

about 3 psi

So your turbo is functional, WG is closing
have you taken it for a real test drive yet?

Yes, the turbo functions properly. Under avg acceleration it would put out 4-6 psi and spike to 9 if you hit the pedal. Of course, it would scream like nuts so I didn't do it too often (to many weird stares from people). I haven't driven it hard yet. I wanted to give the new gasket a chance to seal properly (maybe that's rediculous--I don't know anymore).

I have to leave right away with the truck and will be out for a few hours (got another final exam to prepare for tommorow). Do you think its safe to run it harder now?

If all it is is an air leak, then no danger, just losing a little boost somewhere.
I can't believe the gasket blew on you like that.

I find it strange too. You could tell air has been passing through the gasket because when you normally take the upper intake off, the seal should be white where it was sealed to the contact surfaces right? Well, it was in most places on that seal but there were 2 patches where there was black oil was streamed across the gasket and blowing onto the outside of the intake. Thanks for your help TDG, I really appreciate it. I'll be back in a few hours with an update.

So far so good :D Just finished driving it a few minutes ago. Knowing that the screaming wail would have started at 3 psi, I slowly increased boost to 6 psi and held it there for a number of seconds without a howl. I'm still being easy with it as I want that gasket to bake in there well. Thanks for all your input!!