Strange noise detected. Similar to exhaust leak, but isn't an exh. leak.

Car in question is my '02 Wagon. While running at highway speed, dip into the throttle and I noticed a strange noise. Noise follows RPM and only appears when I give the car 1/4-1/2 (estimated) throttle. Go mild on the the throttle and all is well, no noise.

Longblock is out of an '00 Automatic, complete with 11mm pump, 102k on the motor. Injectors are out of the '02 original motor. I did have to replace one of the tips with a used OEM 5sp tip I had in storage.

Compression is stellar; checked again this morning. 500+psi on all cylinders.

Starts instantly, idles perfect, drives perfect (other than this noise when giving more than 1/2-ish throttle.)

I've checked for exhaust leaks and can't see any evidence of a leak. All manifold nuts are tight, gaskets in place.

Injector mg/stroke deviation via VCDS ranges from -0.4, -0.1, etc. Seems normal.

No evidence of cam/lifter wear as of 1000 miles ago when I put the motor in the car.

Occurs with an EGR block-off plate between the EGR cooler and upper 90° hose, no difference.

If anyone thinks it could be an injector (or even the tip I replaced,) I can swap a 5sp injector from my daily-driver with each of the 1, 2, and 4 injectors this afternoon to eliminate the possibility. At a last resort, I'll swap the 11mm with a known-good 10mm (just not thrilled about it.)

suggestions extremely appreciated.

Had a similar noise that ended up being a boost leak from a loose cooler clamp.

Jesse_Boyer said:

Car in question is my '02 Wagon. While running at highway speed, dip into the throttle and I noticed a strange noise. Noise follows RPM and only appears when I give the car 1/4-1/2 (estimated) throttle. Go mild on the the throttle and all is well, no noise.

Longblock is out of an '00 Automatic, complete with 11mm pump, 102k on the motor. Injectors are out of the '02 original motor. I did have to replace one of the tips with a used OEM 5sp tip I had in storage.

Compression is stellar; checked again this morning. 500+psi on all cylinders.

Starts instantly, idles perfect, drives perfect (other than this noise when giving more than 1/2-ish throttle.)

I've checked for exhaust leaks and can't see any evidence of a leak. All manifold nuts are tight, gaskets in place.

Injector mg/stroke deviation via VCDS ranges from -0.4, -0.1, etc. Seems normal.

No evidence of cam/lifter wear as of 1000 miles ago when I put the motor in the car.

Occurs with an EGR block plate between the EGR cooler and EGR 90° hose, no difference.

If anyone thinks it could be an injector (or even the tip I replaced,) I can swap a 5sp injector from my daily-driver with each of the 1, 2, and 4 injectors this afternoon to eliminate the possibility. At a last resort, I'll swap the 11mm with a known-good 10mm (just not thrilled about it.)

suggestions extremely appreciated.

Click to expand...

This does suggest a boost leak. Do you have VCDS for codes?.
If a visual does not yield an obvious vac line failure or disconnect, then a Mity vac trouble shooting is in order

KAT90 said:

Had a similar noise that ended up being a boost leak from a loose cooler clamp.

Click to expand...

fruitcakesa said:

This does suggest a boost leak. Do you have VCDS for codes?.
If a visual does not yield an obvious vac line failure or disconnect, then a Mity vac trouble shooting is in order

Click to expand...

Yes on VCDS; no codes. Boost control working as it should, just logged it.

I'll look for boost leaks, but it's not that sound at all. (It's not a constant pressure/boost leaking sound.) It sounds exactly like an exhaust leak, I can hear pulses. So, not willing to accept I had good gaskets, I pulled the the turbo and found one gasket was in relatively poor shape. Replaced with another and low and behold, it's still there. Insanely frustrating as it sounds just like an exhaust leak.

ERROR on my part. I simply couldn't hear the leak after 3000 or so. In 2nd gear, it seems to start around 2000rpm and it's done around 3000rpm. It seems to last longer in 3rd gear, but I can't hear it well enough to judge.

Jesse_Boyer said:

Occurs with an EGR block plate between the EGR cooler and EGR 90° hose, no difference.

Click to expand...

Not sure I'm properly visualizing where you are referring to. Do you mean between cooler and the lower EGR Cooler pipe or between the cooler and the upper EGR Cooler pipe?

CopaMundial said:

Not sure I'm properly visualizing where you are referring to. Do you mean between cooler and the lower EGR Cooler pipe or between the cooler and the upper EGR Cooler pipe?

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Cooler and upper pipe (which connects to the cooler and the EGR valve.)

Any other suggestions?
I'm likely to swap injectors tonight, one by one, to see if the noise disappears.

I think the lower EGR pipe or EGR cooler is more likely suspect than injectors.
But that's just a WAG.

Jesse_Boyer said:

Any other suggestions?

Click to expand...

Yes! - Don't worry, be happy!

I can pull the EGR cooler, block it off, and go for a drive. I need to eliminate some possibilities. However, yesterday, when I had the cooler off to pull the intake and turbo, I didn't notice anything abnormal about the EGR cooler or it's pipes. (doesn't mean that isn't the problem though.)

EGR cooler pulled and I moved my block-off plate from the gas outlet of the EGR to the gas inlet (turbo manifold to EGR connection) and no difference was noted.

sound like the copper seal at the bottom of the injector may be leaking. it might show up in a compression test as it would only leak with boost on.

jayb79 said:

sound like the copper seal at the bottom of the injector may be leaking. it might show up in a compression test as it would only leak with boost on.

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Would I see evidence of leakage out of the injector body hole out the top of the head if that were the case?

mine showed soot but it took a few weeks before i noticed it because it was a very light gray that slowly built up. the noise was driving me crazy because i could not figure out were it was coming from until i saw the soot.

jayb79 said:

sound like the copper seal at the bottom of the injector may be leaking. it might show up in a compression test as it would only leak with boost on.

Click to expand...

jayb79 said:

mine showed soot but it took a few weeks before i noticed it because it was a very light gray that slowly built up. the noise was driving me crazy because i could not figure out were it was coming from until i saw the soot.

Click to expand...

Leading money-winner on the TDI-Tour.

Early this morning, I couldn't sleep and couldn't leave well enough alone, so I pulled it apart this morning before work to check the copper injector seals. Low and behold, I knew something was awry as soon as I attempted to loosen the first one. All four definitely felt like they had less than 15ftlbs and I noticed some soot building on #3's hold-down clamp. http://i.imgur.com/AaiSoZz.jpg Blurry picture, but you get the idea. I pulled them all, cleaned the bores thoroughly, and replaced with new washers. At this point the noise appeared to be gone (but I only drove it around the block and took the other car to work this morning.)

SO, if this is the culprit, it turns out it WAS an exhaust leak, it was just a compression leak as well.