Help! Strange whistle at max boost!

[Timbo]

Hi Patrol nuts, (LONG POST)

I've had this problem for quite some time now and it drives me crazy. I've asked around on different forums and still no solution. Hopefully one of you Patrol gurus can give me some insight.

What happens:
When the car is warm (after about 15-20mins of driving) a separate whistle sound emits from under the bonnet. It's not the normal Turbo whistle, it's louder (not fan belt screeching loud), more like a kettle. It's hard to explain. The sound does not occur until max boost, or just under. If max boost is 12psi, I'd say it's happening around 10-11 psi.. in any case, it's right toward the end of the boost limit.

Again, this is a separate whistle sound from the normal turbo whistle.

What I've done:
This has been happening for some time as I said. It's getting harder and harder to remember when it occured. I remember blocking the EGR valve for the first time and then it appeared. I've only made this assumption a while afterwards though.

Originally I thought it was because I squirted WD40 onto my fan belt and I thought it was squealing through slippage.

I've since changed the blocking plate to stainless steel, thinking that aluminium might have been too soft under the heat and warped. Unlikely I know. There appear to be no leaks around the seal.
I have taken the plate out as well and left it standard, only to have the sound still there!

I have blocked all of the rubber hoses off leading to the EGR, taken the butterfly out of the intercooler and blocked the hoses to that, I've tightened up all of the intercooler hoses as far as I can as well.

What I haven't done:

I haven't checked the exhaust manifold or around the waste gate. It could be something to do with the headers not sealing to the block.. but I find it unlikely because this happened to my VL commodore RB30T and that's a really really loud screeching sound.

My Thoughts:

It doesn't happen when it's cold. To me, it's like something is expanding when the motor gets hot and is breaking a seal. Maybe a gasket? It's definitely pressure related. I can virtually make this happen on command in 3rd gear at about 3000rpm (im guessing because my tacho doesn't work another issue!) I can literally accelerate and make the noise appear, then just let off the pedal and it'll go.

I was told that if it was the EGR, if I press the accelerator to the floor hard, then the noise might go away because the EGR shuts off or stops working when under full acceleration. When I tried this, it didn't work. But sometimes, I have noticed under full acceleration the noise does go away all of a sudden. It'll be making the stupid loud whistle sound, then just stop.

My GF said it sounds like it's coming from the snorkel. At this stage, I'm willing to try anything, however silly it may seem. I might fiddle around with the snorkel on the weekend.

It still sounds EGR related to me.. or in that area. I'm buggered if I can figure it out.

What do you guys think?

[patch697]

Your right....thats one long post but top effort detail is good when using chat rooms. You just left one bit out..... What are we talking about here:

What model?

What engine?

Is it inter-cooled?

This info would also help..



Still a top effort well done

Cheers
Paul

[Chris60]

Can't help out with the question but i saw he has a 2.8td GU 1999 wagon on another thread if that helps anyone.

[Timbo]

Yeah sorry Patch, you're right, where's the info on the car.

2.8td GU 99 model intercooled

[YNOT]

Just an idea, 2.8's and some 4.2's had an over pressure boost relief valve on the inlet manifold. Normally these valves open between 14 and 16psi, but the spring in yours may have weakend and be opening earlier. Try cable tying it closed and go for a drive.
If all else fails, put your car on a chassis dyno. Your noise seems reasonably consistent which will make it much easier to replicate.

Tony

[Timbo]

Thanks Tony for your reply.

You just reminded me and I forgot to mention that I was going to ask if anyone knew if there was a boost relief valve.. I thought about the one on the VL and how I blocked that off when I got it intercooled and increased the boost.
I will search for that tomorrow and have a scratch around.

I put the 4wd on a dyno not long ago but they said they didn't hear anything at all and that any sound I might be hearing is the wastegate.. apparently they sometimes do that. I walked away shaking my head thinking... you guys really don't even care at all. They got their $180 and are happy.

cheers

[Timbo]

Hi Tony,

You don't know where the boost relief valve is on the 2.8td do you?
I had a look through the manual I got off this site and it didn't list one. I know where the one is on the VL, it's on the plenum near the throttle body.. but I can't seem to find it on the GU.
Any ideas?

[YNOT]

I was fairly sure all RD28's had them, but I may be wrong. If it's there, it will be on the plenum somewhere.

Tony

[Timbo]

Alright.. i wasnt sure if they had them or not. One would assume that any turbo car has a relief valve but with diesels i dunno. I'll take another gander at the plenum and see what i can find.

[GU89]

Dont know if it will help but the over pressure valve on my 4.2 was on the crossover piping going into the inlet manifold.