No turbo boost when car is warm (1.4TSI)

[Mattlock]

Hi everyone,

About 2 weeks ago my car suddenly decided not to provide turbo boost once it had been driven for about 20-25 minutes. At 3,500RPM, the supercharger disengages and the turbo doesn't cut in. This results is a sudden, noticeable reduction in acceleration and the boost gauge on the dash drops from full boost to about 25%. When cold, it works just fine.

I took it to my mechanic and he ran the codes and it identified an N249 diverter failure, which he replaced with a new part. He said it was a newer revision of the part too. However, the problem still remains, although once in the last 3 days, it failed to have supercharger boost as well.

The fault can be reproduced each and every time and the turbo doesn't return until the car has cooled down.

Interestingly, when it works as normal the car seems to accelerate a bit harder than before maybe as a result of the updated/improved N249.

It's booked in for next week to have another look but I was just wondering if anyone else has experienced similar issues and how easy were they to resolve.

[mythik]

Experienced the very same problem - the root cause was the supercharger clutch was slipping when it was warm. Replacement clutch fixed it right up.

[h100vw]

Why would the supercharger clutch stop the turbo from working???? I am not seeing that....

[Mattlock]

No turbo boost when car is warm (1.4TSI)

Why would the supercharger clutch stop the turbo from working???? I am not seeing that....

Yeah, I was in the middle of saying the same thing!

The supercharger works fine. It provides boost up to 3,500RPM regardless of the operating temperature. The boost is missing from 3,500 upwards.

I wonder if I have a vacuum hose not sealing properly and expanding when hot.

[mythik]

Why would the supercharger clutch stop the turbo from working???? I am not seeing that....

I know. I said the same thing at the time. the two are not connected. dead spot after supercharger should disengage.

the invoice for repair cited a replacement clutch for the supercharger and the problem was gone! go figure.

[Mattlock]

No turbo boost when car is warm (1.4TSI)

I know. I said the same thing at the time. the two are not connected. dead spot after supercharger should disengage.

How odd. Every time it's done it in the last 2 weeks, there's been no dead spot, the turbo is just MIA! However on the drive home tonight, I had a dead spot; no boost between 3,500 and 4,000 and then it suddenly came back and surprised me and nearly caught me out!

You could be right...

[Mattlock]

No turbo boost when car is warm (1.4TSI)

the invoice for repair cited a replacement clutch for the supercharger and the problem was gone! go figure.

Out of interest, was that all that was changed? Do you mind if I ask How much it cost to fix?

[Paul_OH]

Try the N75 valve also, I had the same symptoms, changed both and all was sorted (N75 should be well under $100)

[Mattlock]

No turbo boost when car is warm (1.4TSI)

Try the N75 valve also, I had the same symptoms, changed both and all was sorted (N75 should be well under $100)

OK. So what does that one do? I assumed it was the diverter for the supercharger and as it is working fine wouldn't need to be touched.

The only fault code when it did it before the N249 replacement was for the N249. Are the codes cascaded with the most important only showing and secondary codes suppressed?

The mechanic is going to take another look at it on Tuesday so I'll report back after that.

[h100vw]

OK. So what does that one do? I assumed it was the diverter for the supercharger and as it is working fine wouldn't need to be touched.

The only fault code when it did it before the N249 replacement was for the N249. Are the codes cascaded with the most important only showing and secondary codes suppressed?

The mechanic is going to take another look at it on Tuesday so I'll report back after that.

All faults will be held until deleted.

[Paul_OH]

The N75 is the charge pressure control solenoid. I'm not exactly sure what the correlation is between the 2 but when I had the N249 error code, replacing that valve only didn't solve it - only when the N75 was changed also. My N249 Diverter valve was completely screwed though with a torn diaphragm - make sure that the new one fitted is the newest type with a piston instead of diaphragm (VW upgraded it a couple of years ago).

[Mattlock]

No turbo boost when car is warm (1.4TSI)

The N75 is the charge pressure control solenoid. I'm not exactly sure what the correlation is between the 2 but when I had the N249 error code, replacing that valve only didn't solve it - only when the N75 was changed also. My N249 Diverter valve was completely screwed though with a torn diaphragm - make sure that the new one fitted is the newest type with a piston instead of diaphragm (VW upgraded it a couple of years ago).

Ok. This makes a bit more sense and matches with the reading I've been doing. Forge Motorsport make a valve-based replacement that still hooks in to the stock ECU and it seems to only replace the N249, supposedly eliminating the N249 failures.

My mechanic went out of his way to tell me that the part had been revisions by VW and I had that newer part fitted last week.

[Mattlock]

So, my mechanic has been through the car again and cannot find any fault codes for the problem but on a test drive with me acknowledged that the problem is still there (can't really miss it).

He ran some specific diagnostics on the N75 and in isolation it appears to be playing up. He wants to understand why there's no fault code for it so he's going to play with it next week whilst I'm overseas before simply replacing the N75.

[Mattlock]

No turbo boost when car is warm (1.4TSI)

He ran some specific diagnostics on the N75 and in isolation it appears to be playing up.

The car is back after a holiday with the mechanic (I was overseas all week anyway). They confirmed it was the N75 that was causing the issues. They replaced it and drove the car cold and hot to make sure it was well and truly fixed.

They said that for some reason the TSI doesn't report in as much detail as the GTI and that apart from voltage nothing else about the N75 is reported up as a fault code. Therefore you only find it's faulty when you run specific diagnostics against the unit.

So it's ended well with the car being returned to full boost after replacement of both N249 and N75. Now for the APR Stage 1 tune...

[The One]

The car is back after a holiday with the mechanic (I was overseas all week anyway). They confirmed it was the N75 that was causing the issues. They replaced it and drove the car cold and hot to make sure it was well and truly fixed.

They said that for some reason the TSI doesn't report in as much detail as the GTI and that apart from voltage nothing else about the N75 is reported up as a fault code. Therefore you only find it's faulty when you run specific diagnostics against the unit.

So it's ended well with the car being returned to full boost after replacement of both N249 and N75. Now for the APR Stage 1 tune...

APR stage 1 tune on the 1.4L Twin charged... People are mad.