Refurbished turbo problems....any ideas?

T

TAABVW

A2OC Donor
I am fixing up a TDI90 for my son when he passes his test. One of the repairs was reconditioned turbo from Midland Turbo's. When the turbo arrived back I was very pleased to see that the only original part appeared to be the casings, everything else looks new. Having installed it in the car I now have the following problem. It seems to behave as if the variable vanes are not there. At full throttle at 1600rpm it only gives 1.1bar (my other tdi90 gives 1.6bar) at 2000rpm it only produces 1.6bar (my other tdi90 produces 2.5bar. Over 2000rpm it does produce 2.2bar but this is still down on the 2.4/5 it should be giving.

Checks I have done:

On fitting it was primed with fresh oil. New gaskets, nuts etc.
I've temporarily blanked off the egr to ensure it is not stuck open.
I've disconnected the exhaust downpipe to ensure that a blocked cat is not causing excess back pressure.
I've pressure tested the boost pipes and intercooler in-situ from the turbo to the anti shudder valve.
I've swapped the MAF with my other tdi90 to rule that out.
I've swapped the inlet pressure sensor with my other tdi90 to rule that out.
I've checked the vacuum system and confirmed that the vane actuator rod is fully pulled in at tickover.

It drives and gives no VCDS codes but its just totally gutless below 2100rpm.

Midland turbo have invited me to send the turbo back and they will check it but obviously I will now have to remove it from the car again.
I desperately don't want it to be a duff refurb or more likely maladjusted variable vane mechanism. The only way I can categorically prove or disprove the turbo is at fault is to swap it with a known good turbo from the other tdi90 but that's a lot of bad back knuckle scraping.

Do any of you mechanical geniuses have any other ideas I could try?
 
If you can find a helper with vcds, you can measure (I think) requested boost against actual, just to confirm the turbo is the culprit.
Mac.
 
What was the reason for changing the turbo in the first place, could there be another issue with the engine that's preventing the boost from being achieved, eg leaking intercooler, or faulty G75 assembly?
 
Have known N75 valves to cause issues and the black and white one way valve fitted wrong way around
 
TAABVW said:
I am fixing up a TDI90 for my son when he passes his test. One of the repairs was reconditioned turbo from Midland Turbo's. When the turbo arrived back I was very pleased to see that the only original part appeared to be the casings, everything else looks new. Having installed it in the car I now have the following problem. It seems to behave as if the variable vanes are not there. At full throttle at 1600rpm it only gives 1.1bar (my other tdi90 gives 1.6bar) at 2000rpm it only produces 1.6bar (my other tdi90 produces 2.5bar. Over 2000rpm it does produce 2.2bar but this is still down on the 2.4/5 it should be giving.

Checks I have done:

On fitting it was primed with fresh oil. New gaskets, nuts etc.
I've temporarily blanked off the egr to ensure it is not stuck open.
I've disconnected the exhaust downpipe to ensure that a blocked cat is not causing excess back pressure.
I've pressure tested the boost pipes and intercooler in-situ from the turbo to the anti shudder valve.
I've swapped the MAF with my other tdi90 to rule that out.
I've swapped the inlet pressure sensor with my other tdi90 to rule that out.
I've checked the vacuum system and confirmed that the vane actuator rod is fully pulled in at tickover.

It drives and gives no VCDS codes but its just totally gutless below 2100rpm.

Midland turbo have invited me to send the turbo back and they will check it but obviously I will now have to remove it from the car again.
I desperately don't want it to be a duff refurb or more likely maladjusted variable vane mechanism. The only way I can categorically prove or disprove the turbo is at fault is to swap it with a known good turbo from the other tdi90 but that's a lot of bad back knuckle scraping.

Do any of you mechanical geniuses have any other ideas I could try?
Click to expand...
An excellent question, as in lots of info and lots of sensible things done. As above, the one thing you didn't mention is why the turbo was changed in the first place? I assume noisy / using oil / endfloat?

I have rebuilt one VNT turbo in my life, using a Chinese cartridge: don't laugh, many of the big refurb co's now fit them rather than the Eastern European options. Anyway the one thing that was underlined to me is that the alignment between the cartridge and the outer body is absolutely critical. As I'd bought mine via a friend of a friend, mine came from a big-name refurbishment Co, send by the MD. Essentially he said to try it by referencing the existing dimensions but if it didn't pull right they'd need to take it in and adjust it for me.

In the absence of anything else, this might give a clue, although in my case it worked perfectly and pulled like a train throughout with no limp-mode or codes.

Sadly many Co's are happy to send kit out, and indeed replace it, but less keen to pay your costs for the whole replacement process.
 
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Catnip64 said:
What was the reason for changing the turbo in the first place, could there be another issue with the engine that's preventing the boost from being achieved, eg leaking intercooler, or faulty G75 assembly?
Click to expand...
The previous owner had run the car with a leak in the intake pipe. Unfiltered air over time had damaged the leading edge of the impeller. It was also leaking oil. Pressure tested intercooler and vacuum is pulling on the vane adjuster, which I think rules out the G75.

Trevor
 
spike said:
Not sure if this is the same layout as the 90 tdi turbo but this 'advert' provides some info on the complexity of adjusting it

Turbocharger VNT Calibration - UK

Get your turbocharger VNT calibrated here!
www.turborebuild.co.uk www.turborebuild.co.uk

Cheers Spike
Click to expand...
Thanks for that Spike. So it could be that Midland Turbo have forgotten to set the stop screw. Thar would fit the symptoms. I'll try and get a look at it with a mirror to see if they have any tamper paint on the stop screw. Not that I will adjust it as this would likely invalidate the 2 year warranty but the presence of paint would suggest they had adjusted it and vice versa.

Trevor
 
TAABVW said:
I've checked the vacuum system and confirmed that the vane actuator rod is fully pulled in at tickover.
Click to expand...
What does that mean exactly? Does the rod move when going from tickover to 2000rpm? Have you checked the actuator diaphragm?

RAB
 
RAB said:
What does that mean exactly? Does the rod move when going from tickover to 2000rpm? Have you checked the actuator diaphragm?

RAB
Click to expand...
Hi RAB. As I understand it the vacuum system pulls on the actuator rod to adjust the vanes to the high boost position when the engine is at tickover speed. Thus maximum possible boost is achieved at low revs. At tickover speed the vacuum system is indeed pulling on the vane actuator rod proving the diaphragm is intact. A few seconds after the engine is switched off the vacuum is released and the actuator rod moves back to its "rest" or lower boost, max exhaust flow position.

I have not checked if the actuator rod moves from tickover to 2000rpm, I suspect it shouldn't as this is the high boost phase. If the rod is pulled by the vacuum at tickover I think it should give me max possible boost........and it doesn't.

I'm happy to be corrected.

Thanks

Trevor
 
TAABVW said:
Thanks for that Spike. So it could be that Midland Turbo have forgotten to set the stop screw. Thar would fit the symptoms. I'll try and get a look at it with a mirror to see if they have any tamper paint on the stop screw. Not that I will adjust it as this would likely invalidate the 2 year warranty but the presence of paint would suggest they had adjusted it and vice versa.

Trevor
Click to expand...
tamper paint1.jpg

tamper paint2.jpg


As can be seen in the above photos, there is tamper paint on both the rod position and the stop screw position which suggests that they have been set. Of course its not impossible that tamper paint could have been applied without a setting taking place, but more unlikely I think.

Trevor
 
N75 is often missed as the true cause of loss of power. It is a solenoid valve so hard to test but worth swapping for a known good one
 
TAABVW said:
I have not checked if the actuator rod moves from tickover to 2000rpm, I suspect it shouldn't as this is the high boost phase. If the rod is pulled by the vacuum at tickover I think it should give me max possible boost........and it doesn't.
Click to expand...
As long as you can see some movement of the rod, you can probably exclude the turbo itself. If not, check the actuator by attaching a piece of tube to the actuator and suck on it. If there is no resistance, the diaphragm is U/S.

Are your vacuum connections correct? Cross-check the manifold connections with your other Tdi90.

RAB
 
Howey said:
N75 is often missed as the true cause of loss of power. It is a solenoid valve so hard to test but worth swapping for a known good one
Click to expand...
Good shout. I have just gone out and swapped the vacuum manifold, which I think serves as the N75 in the tdi90, with my other tdi90. Alas no difference.

Thanks

Trevor
 
RAB said:
As long as you can see some movement of the rod, you can probably exclude the turbo itself. If not, check the actuator by attaching a piece of tube to the actuator and suck on it. If there is no resistance, the diaphragm is U/S.

Are your vacuum connections correct? Cross-check the manifold connections with your other Tdi90.

RAB
Click to expand...
Yes the vacuum is definitely moving the vane actuator rod.

Good idea with the possible mix up of vacuum tubes.I have now checked against other car and unfortunately all is correct.

Thanks

Trevor
 
I set up a camera to view the vane actuator rod whilst driving (with passenger). The rod is pulled in the high boost position from tickover to about 2200rpm. Only then does the rod start to move the vanes to the high exhaust flow, lower boost position and that is when I get some power. It really does feel as if the vanes are closing completely in the high boost position thereby hardly providing any boost.

I'm a bit stumped and think I will have to remove turbo tomorrow and return to Midland Turbo.

Thanks for suggestions all.

Trevor
 
Maybe the linkage is disconnected internally, although on a Garrett turbo if that happens, it won't bolt together. It's quite tricky to re-unite the parts.

RAB
 
@TAABVW Do you have detailed history what happened to the car repair and maintenance wise? How was the car driving before the turbo was send away for Overhaul?

A while ago I experienced similar behavior from my ATL. Long story short, someone put in AMF injectors, including ECU mapping, which is suitable for a wastegate turbo, but did not (duh!) could manage a VNT turbo obviously......

Poor performance 1st and 2nd gear ATL/TDI 90 below 2000rpm.

https://www.a2oc.net/community/index.php?threads/new-6-speed-gearbox-method-passat-11-onwards-myp-gearbox.25919/page-15#post-453268 A separate topic so the 6 speed gearbox topic (link above) will not be hijacked. Sorry for the inconvenience Well, what can I say; I'm very surprised with my ATL...
www.a2oc.net

If a car had multiple owners it's not always clear what is done to it, or if there are choices made on financial grounds. Some owners don't care, as long as the vehicle drives they're happy.
 
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