Intermittent loss of power

[03_JettaTDI]

Hey

I've got a 2003 Jetta with the ALH, 322,000 kms, and a manual transmission. I've owned the car for just over 2 weeks now, and the previous owner said he had the same problem with a lack of power only sometimes.

I did some looking while the car was running, and I've determined its on the turbo side, specifically the actuator for the turbo is keeping the vanes closed when it warms up. I'm thinking its likely a failure with the N75, but I was unsure if it would be electrical as well.

Some insight would be great
Thanks

 

[oilhammer]

What DTC(s) does it have? Is the boost tracking actual vs. requested?

 

[03_JettaTDI]

I tried plugging my scanner but it wouldn't read. It doesn't pull up any engine lights when it loses power so I'm wondering if there's gunk in the N75 or a short somewhere

 

[oilhammer]

Well, you can guess.... but sounds to me like you need to avail yourself of a suitable scan tool. The ECU controls, and thus monitors, boost. If it goes off, it will set a DTC. On that one, it will flag both OVER or UNDER boost.

You may be chasing your tail without the proper equipment. Heck, a fruity brake light bulb can cause this.

 

[Mpaw]

you could try unplugging the pipe n the actuator, put your finger over it. You should have vacuum. If someone revs it up the vacuum should reduce.
If this works so, your N75 would appear to be ok. If not could be N75 or a number of other things (mostly leaky pipes). Might be worth trying to find air leaks before you buy anything.
BTW: unlikely it's gunked up, they're just vacuum and electrical
But as Oilhammer wrote (as I was typing), you don't get so far without a decent scanner

 

[03_JettaTDI]

I borrowed a decent scanner for a bit here, and it came up with an over boost code. And originally I had pulled the vacuum line off and there was good vacuum, so it must be an electrical short somewhere.

 

[oilhammer]

OK, overboost is almost always a sticking turbo. Rarely it can be an N75, if the vent line was left loose from the air cleaner long enough the vacuum system will suck in a bunch of debris from unfiltered air. But chances are better the turbo is just kaput. You might be able to clean/lube it and get it working again.

 

[03_JettaTDI]

Okay I had wondered about stuck vanes. will I have to pull the whole turbo apart then?

 

[oilhammer]

Replace the turbo. You can certainly try to free it up, if you place a very low value to your time. But... the turbo may not even come apart (bolts break, housing won't come out... because it's spent 20 years and who knows how many kilometers in Canada), then even if you DO manage to get it apart, the actual ring inside may be so worn that it won't really matter.

Up to you. If I could not free the mechanism up from the underside with the assembly all on the engine, then I'd plan on getting a new turbocharger.

 

[03_JettaTDI]

Okay good to know. I don't know if I can warrant changing the turbo without first seeing if I can free it up, they're not all that cheap up here for a stock turbo. But thanks

 

[oilhammer]

I use one of these tools:

https://www.grainger.com/product/2TVX1?gucid=N:N:PS:Paid:GGL:CSM-2295:4P7A1P:20501231&gclid=Cj0KCQjw9rSoBhCiARIsAFOiplmyWdoDs_lWn48D1daxskFFLyWrsLZ5iRnteMtwHLSvxqPyLpcBshkaAvYLEALw_wcB&gclsrc=aw.ds

Go up from underneath, behind/over the steering rack, and you can manually move the end of the VNT actuator (where the rod attaches) up and down, and spray some penetrating oil up there while doing it. I then use a hand vacuum pump directly attached via a small section of vacuum line to exercise the actuator. When vacuum is released, see if it goes all the way back to rest (use the tool to push it back up). If it doesn't, then that is the problem.

 

[J_dude]

Where in Canada are you located? You may be able to get access to VCDS from another member here.

 

[snakeye]

Replace the turbo. You can certainly try to free it up, if you place a very low value to your time. But... the turbo may not even come apart (bolts break, housing won't come out... because it's spent 20 years and who knows how many kilometers in Canada), then even if you DO manage to get it apart, the actual ring inside may be so worn that it won't really matter.

Up to you. If I could not free the mechanism up from the underside with the assembly all on the engine, then I'd plan on getting a new turbocharger.

Yup pretty much this. If the vnt control ring is worn, it'll seize up again in no time. My rule is if you're buying an ALH, get a new turbo. Installed one on my latest car after purchase; best thing I could've done. It's been running trouble free for the last 100k km, which certainly wouldn't have been the case had I kept messing around with the old turbo. Idparts has remanufactured ones, which are basically new, at decent price.

 

[pkhoury]

Okay good to know. I don't know if I can warrant changing the turbo without first seeing if I can free it up, they're not all that cheap up here for a stock turbo. But thanks

If you're 100% stock, you can get a new Melett turbo from darkside developments:
https://www.darksidedevelopments.co...r-for-1-9-tdi-vw-golf-mk4-90-100-110-115.html

I've used both the VNT17 equivalent and a Garrett VNT17 I've found at the junkyard that was like new (I got lucky several times).
Just like how Garrett is owned by Honeywell, Melett is owned by WABTEC (think Westinghouse air brakes). They're supposedly made in China in an ISO facility but assembled in the UK. Never had a problem with them and it beats trying to waste time fixing an old worn out turbo or shelling out $800+ for a new VNT15.

 

[Mpaw]

they are probably right (turbo is kaputt). But you can quite cheaply completely test the N75 etc first if you are really skint

 

[P2B]

OK, overboost is almost always a sticking turbo.

Not in my experience here in the salt belt, half the time it's just a rusted out actuator.

OP needs to disconnect the actuator arm from the turbo to determine which is the issue.

 

[oilhammer]

How does a rusted out actuator enable the VNT rod to move into the boost position if it cannot hold vacuum?

 

[DuraBioPwr]

Turbos are service items. I would just put a new one on it. Mine was sticking too. The ring was warn in one spot and would stick there.
At 322,000KM its done its time and owes you nothing.

 

[P2B]

How does a rusted out actuator enable the VNT rod to move into the boost position if it cannot hold vacuum?

Rusted out might be the wrong term. They get partially filled with rusty looking dust. You can hear it when you shake them and it falls out the vent hole. They usually still hold vacuum but rod movement is limited and causes an overboost code.

 

[oilhammer]

Ah, OK, that sort of makes sense. Also possible that the N75 is ingesting a bunch of debris, which could cause the vacuum to not release properly. I've seen that, too. You guys certainly see more rusty turbo bits than I do.

 

[snakeye]

Ah, OK, that sort of makes sense. Also possible that the N75 is ingesting a bunch of debris, which could cause the vacuum to not release properly. I've seen that, too. You guys certainly see more rusty turbo bits than I do.

Had a brand new Garrett actuator rust out in a 2-3 years, just as described above. Really sucks up here in the rust belt. On my latest turbo which I purchased new, I added a rubber boot that covers the hole on the top, which came off a "cheaper" non oem actuator. We'll see if that makes a difference.

 

[wonneber]

Rusted out might be the wrong term. They get partially filled with rusty looking dust. You can hear it when you shake them and it falls out the vent hole. They usually still hold vacuum but rod movement is limited and causes an overboost code.

VW had a bulletin about the actuator rusting internally.
I had mine replaced under the emissions warranty.

 

[03_JettaTDI]

Sorry for the delay in response, but I will look into replacing the turbo. It does however spool relatively quick and sounds good the way that it is. I tried the oven-cleaner trick to remove most of the carbon from inside the exhaust side, and the vanes did free up but now the car is more gutless than before. In which case it would be easier to change the turbo.

 

[P2B]

In which case it would be easier to change the turbo.

Actually it would be easier (and a lot cheaper) diagnose the issue before replacing parts.

Did you test the actuator and N75?

 

[03_JettaTDI]

Actuator is good, and from what I can see the N75 is actually operating as intended. However as I'm just grasping at straws I'm thinking I might have an underfueling problem, if such a problem exists.

 

[LeisureDave]

Actuator is good, and from what I can see the N75 is actually operating as intended. However as I'm just grasping at straws I'm thinking I might have an underfueling problem, if such a problem exists.

I had intermittent power loss in my alh from air bubbles in the fuel system

 

[03_JettaTDI]

That could be something to check. I did notice my turbo does leak a little bit of oil so could that be a possible loss of boost?

 

[03_JettaTDI]

Nevermind I found my problem. MAF sensor was dirty, and had way more power when I unplugged it.

 

[wonneber]

Long shot if you haven't replaced the turbo.
When I had over boosts for a while I would drive the car on the highway going to work.
When the engine temp was up I would pull over to the shoulder for a few minutes and when it was clear I would start going and give it an Italian tune up.
Not to red line though.
Took a week or so doing this both ways to straighten out.
Did the tune up once or twice a week getting on to the highway to keep things working.