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Discussion Starter #1
Hello.

Me and my girlfriend recently bought a 1998 new beetle tdi. We love the car. However it has that hissing sound when under load. The car still pulls fine and doesn't have any noticeable loss of power.

Because I don't have a "before" and "after" to compare I'm not 100% sure if it has a boost leak or not. I undid the accordeon pipe between the intake and the EGR valve and injected 5 psi in there. It was holding pressure no problem. Did I do that right? Do I need someone in the car to press the gas pedal or something like that? I don't have much experience with TDIs...

Also I read a lot about EGR cooler failures and a possible cause of hissing...how can I troubleshoot that short of taking it out and bench-testing it? When the car is not running the AGR valve is completely closed right? So no recirculation possible?

I guess my next step is going to do the same test with 10-15 psi and see if I can hear anything.

Any suggestions?

Thanks for helping a newbie!
 

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How loud is that? Are you hearing it when inside driving, or outside listening to the engine?

The turbo when engaged doesn't make a ton of noise, you might just be hearing that? Is it a constant noise at a specific RPM, or specific speed? Is it noticed about 1 second after you press down hard on the accelerator to increase speed?
 

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Discussion Starter #3
I can hear it from inside the car. It's definitely load-related i.e. if I just cruise along then I can barely hear it but when I give her and the turbo spools up then it gets louder.

It's gotta be too loud to be normal. Do you know the correct procedure to do a boost leak test to pressurize the whole intake? I'm hearing different things...

Thanks for the help.
 

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if you want an easy hillbilly boost test leak get a gallon ziplock baggie or larger bag that is fairly thick. with the car off pull off the air filter box and use the clamp to put bag inflated over the intake hose, clamp it down. gently compress the bag and look for leaks. easy cheap and works way to well.
 

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One quick thing to check is if your lower IC piping is secure. Just go to the passenger front and feel up in front of the wheel well. You'll feel a pipe and some clamps. The lower IC exits into a pipe which then goes to the turbo. Mine wiggled off the other day (installed metal pipes and didn't clamp the T-Bolts down enough). When I revved I heard a hiss. Either way, there's probably just a loose pipe, inspect them and wiggle them around. I don't know how to access the upper IC pipe though. It runs to the left of the timing belt and then goes 'down' somewhere.
 
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