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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old October 15th, 2019, 23:36   #1
hey_allen
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Default SOLVED - No boost and strange noise after replacing failed turbo

I had my original turbo fail yesterday morning, while on my commute to work.
The symptoms were a bang or pop, followed by loss of power, and a white cloud in my exhaust.
Once I got off of the road, I also found oil dribbling from behind the engine.
Once I had the car towed to my garage, and I had it up on jack stands, I found that the oil was coming from a split in the downpipe, just after the elbow.
A newly rebuilt turbocharger with a complete center housing replacement was installed, using a new braided oil supply hose and a spare downpipe salvaged from a scrapped car.
After installing the new hardware, I primed the turbo oil supply by cranking with the injection pump unplugged, 20-30 seconds at a time, multiple cycles.
When I finally reconnected the injection pump and cleared the fault codes, it had no boost at all.
Once I tried revving the engine off of idle, it almost immediately made a short screeching noise, which prompted me to shut it off.
Does anyone know what may have been happening, other than a bad turbo cartridge?
I haven't pulled the inlet hose to check rotation yet, as by the time I had everything buttoned up, it was dark and getting cold, as well as just wanting some time to think about it before digging into it again.
Any input would be appreciated.

Last edited by hey_allen; October 20th, 2019 at 19:32.
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Old October 16th, 2019, 00:08   #2
Meister Kraft
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Quote:
Originally Posted by hey_allen View Post
After installing the new hardware, I primed the turbo oil supply by cranking with the injection pump unplugged, 20-30 seconds at a time, multiple cycles.
When I finally reconnected the injection pump and cleared the fault codes, it had no boost at all.
Once I tried revving the engine off of idle, it almost immediately made a short screeching noise, which prompted me to shut it off.
Does anyone know what may have been happening, other than a bad turbo cartridge?
Take the night off and relax that’s my advise, it is cold out tonight and the rain is coming. I’ve done more damage than good when i’m frustrated.

I would Clean the oil out of the plastic inlet tube to the turbo and the pressure side to the intercooler. It sounds like you may have an air leak from bad fitment from oil expanding the rubber parts or and exhaust leak.

The best way that I know to find leaks is with a smoke machine, if you don’t have that tape a paper towel to a stick and look for soot or a lot of movement on the exhaust side. Also disconnect the down pipe to see if the oil has clogged the cat enough to raise back pressure.

Edit:

I found a post about the EGR system being added on in the last 4 days, check over that system for leaks also. A cracked egr cooler can whistle an awful noise, only seen it once but it’s worth checking.

Last edited by Meister Kraft; October 16th, 2019 at 00:23. Reason: Sounded really snarky
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Old October 16th, 2019, 03:42   #3
Tdijarhead
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Make sure all the connections for the egr pipe are secure and tight. Those metal oval gaskets are like a reed in a musical instrument if you don’t get the bolts tight, they make an incredible noise. A high pitch screech.
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Old October 16th, 2019, 08:15   #4
hey_allen
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The downpipe was ruptured at the flex joint, just after the turbo flange, so I replaced it from a car that was parted out.
I'll check all the joints again, but I'm thinking that at least SOME boost would show, if there were minor leaks.
I checked that all the boots were fitted after the initial test, and they were.

Using Torque app to monitor boost, it actually showed slight vacuum on the gauge, increasing with engine rpm, instead of any boost. 1.9 inHg at idle, to 3.2 inHg at higher rpm.


I'll definitely check the plumbing again, as well as talking to the shop that rebuilt the turbo to see if they have any input.
I'm planning to pull the intake hose back off to verify that the turbo is actually freely turning. I definitely remember checking end-play, since that was an issue before that turbo was sent to rebuild, and which drove the replacement of the rotating assembly.


My car's old turbo failed dramatically. I thought it was just an oil seal failure, but once I got the downpipe off of the exhaust side, I realized that there was ~1/2" of axial motion, and freely wobbling as well. It appears to have split shaft supporting the wheels...
I got LUCKY that there was not a runaway condition.
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Old October 16th, 2019, 08:40   #5
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Before putting the rebuilt turbo in, did you check if there was any debris from the old turbo in the intake ducting? Something might have gotten sucked in immediately and jammed the new turbo.

If that's not it, then my guess would be that the rebuild was just no good.
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Old October 16th, 2019, 12:55   #6
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We can get 2 birds with 1 stone if you undo the down pipe. You can check the turbo charger wheel, run the vehicle to see if boost returns or the whistle/reed noise is gone. If that works then we know the exhaust is the issue.

When a turbo dumps oil in the exhaust the converters can plug from oil cooking itself.
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Old October 16th, 2019, 20:26   #7
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I understand that a new turbo costs more than a 'rebuilt' one. But...
Check the runout at the impeller and for contact on the housing.
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Old October 16th, 2019, 20:44   #8
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...or we can skip ahead to where did the "completely rebuilt" turbo come from.

A vacuum line accidentally left disconnected during the swap could cause these symptoms as well.
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Old October 16th, 2019, 20:57   #9
hey_allen
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The rebuild was from DFIS in Portland, and after talking to them this morning, they were asking for me to send in the new turbo.
That said, I am pulling the intake and checking for free rotation tonight.

I was checking to see if any of the vacuum lines could have been incorrectly reinstalled, but the only three disconnected would have been easily discovered.
VNT actuator, EGR valve, and the short line from the ASV solenoid to the ASV actuator.

The cat should not be an issue, since it was replaced with one from a neighbor's car that was sideswiped by a work van. He'd been driving it regularly until that happened.

Last edited by hey_allen; October 16th, 2019 at 20:59.
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Old October 16th, 2019, 21:12   #10
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So, after pulling the intake hose off of the turbo, I found it spins freely, with no detectable axial or radial motion.
I'm scratching my head now...

I unplugged the N75 valve, just to see if anything changed, and the screeching went away.

Using VCDS group 11 to test the N75 valve at idle, it does nothing.
EGR test worked as expected, but none of the manifold pressure tests ever so much as twitched.

Last edited by hey_allen; October 16th, 2019 at 22:29.
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Old October 16th, 2019, 22:40   #11
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Based on a distinct lack of screeching when the N75 is disconnected, I am curious if it's possible to somehow reassemble the vnt blades in a way that they could touch the hot side of the rotating assembly when actuated?

Last edited by hey_allen; October 17th, 2019 at 07:06.
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Old October 17th, 2019, 06:28   #12
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Watching this and scratching my head
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Old October 17th, 2019, 06:41   #13
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Sounds like the blades are striking the housing when boost is requested. When you disconnect the N75 it can't make boost, so no noise. Why? Not sure. Lots of possibilities, including faulty rebuild, foreign object damage or oil contamination damaging the shaft after install, boost leak somewhere else in the system. Those are some.
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Old October 17th, 2019, 07:53   #14
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I think if the VNT actuator is adjusted incorrectly, it could cause the vanes to interfere with the turbine wheel. You can probably test that by applying vacuum to the VNT actuator with a MityVac (or something similar), and trying to manually spin the turbo.

The bad news is, if that's what's happening, then your new turbo is junk. Because the vanes and the turbine will both be damaged.
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Old October 17th, 2019, 10:16   #15
hey_allen
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So, last night I tested a few different things, including applying vacuum to the actuator while it was at idle, which did not cause any noise.
Idle may not have had enough airflow to spin up the turbo.


The shop that did the rebuild is sending another center cartridge assembly, so I'll be swapping the CHRA next week, and taking a close look to see if I can find anything obvious.

I'm thinking to try disconnecting the intercooler plumbing from the turbo and the EGR valve, and plugging both ends. I can apply pressure from a regulated source, which should show if there are leaks that part of the system.
That said, it never indicated any boost, so I doubt that it's a split in the air path.


Testing the Group 11 functions in VCDS last night, I saw and heard change to the engine RPM when the EGR N18 solenoid was tested, but no change at all when the VNT actuator N75 solenoid was tested.
With the engine off, I could hear the actuator moving with the test, so it appears that the N75 works, just something appears to be off in the turbo.
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