Random loss of boost

[Greggo]

I was doing my 20 mile commute to work this morning, and was on motorway and put my foot down to get on to the slip road, probably 3rd gear (around 2k revs) expecting the normal turbo boost to propel me up the slope and to join the main traffic, but there was no turbo boost? I thought that it may just need to have full throttle held down longer, but there was nothing, almost like driving a normally aspirated diesel, except I could hear the actual turbo whistling sound which sounded normal.

All the way, when i had the throttle open it didn't seem to be boosting at all. I parked up puzzled and on the drive home i throttled it a few times and the boost seemed to return, albeit as first not as strongly as normal.

Did a drive before and the boost is back to normal.

Could this random loss of boost be that there was a blockage somewhere that needed clearing? I don't always use the boost that often in normal driving, just the odd blast up the slip roads and when on motorways or the a-roads..

Perhaps Im being too soft with it?!

 

[zach225]

could be a faulty maf sensor, there isnt really anything to get blocked and even if you dont boost it if a long time the car will still have boost there ready,

might be worth a vagcom scan

 

[Brazzer71]

my car (leon 140pd) did this recently, apparantly its the variable vane turbo not changing over to lower pressure as the engine revs increase, and so the ecu see's over pressure and opens the waste gate to stop the boost. it then all resets when you switch it of and on again.

easy fix though, added two bottle of forte fuel treatment to a quater tank of fuel and took it for good blast, that cleaned every thing out and its been fine since, even doing more mpg now.

 

[coolypops]

This is commonly referred to as "limp mode" here.
If you do a search you'll get loads of results.

It is a setting which the ECU sets itself to, to protect the tubo from damage.

The most common causes are:

1. boost leak
solution - find and repair boost leak.

2. dodgy MAF sensor.
solution - change sensor.

3. vanes in turbo sticking.
solution - clean/recondition/replace turbo. (Google innotec turbo cleaner/ go here http://forums.tdiclub.com/showthread.php?p=1340914)

4. VNT actuator on its last legs (although not as common as the other three)
solution replace VNT actuator.

It might be a good idea to get the car diagnosed on VAG-COM before doing any work...



Also as regards being too soft with it the recommended way to drive a TDI is:

Start it and give it 20 - 30 secs to let the oil pump around the engine,
Drive it up to 2500 rpm before changing gear, until you reach the line on the temp. gauge before the one which the needle rests at,
Then drive it up to 3500 rpm before gear changes.
When stopped let the car idle for 10 - 30 seconds to let the turbo spool down as they spin at over 100,000rpm under boost and just knocking the engine off stops the oil flow, causing excessive wear and premature turbo failure.

This method of power cycling prevents soot buildup on the turbo vanes and catalytic converter and leads to long engine life.
Babying them only leads to excessive soot buildup.
This is recommended by some of the 250k+ milers on TDIClub and I'm on 130k miles and she's still purring like a turf burning kitten...



And with regards to Brazzer71:

my car (leon 140pd) did this recently, apparantly its the variable vane turbo not changing over to lower pressure as the engine revs increase, and so the ecu see's over pressure and opens the waste gate to stop the boost. it then all resets when you switch it of and on again.

easy fix though, added two bottle of forte fuel treatment to a quater tank of fuel and took it for good blast, that cleaned every thing out and its been fine since, even doing more mpg now.

This would most likely be the beginnings of your turbo vanes sticking, so I'd recommend cleaning your turbo before you do have problems... see above...


Whew, long post...

 

[Greggo]

Cheers for the info thats really useful to know, because im a noob to the TDi world!

Must have been restarting the engine that helped reset it, and when driving it today the boost is back and feels better than before almost.

Its on nearly 165k too (bought it cheap for an 02 FSH new cambelt clutch), and certainly doesnt feel it.

Had the car a month and yesterday was the first time its ever done that, but will certainly take the advice given... im wondering if it was a hot switch off the night before that may have upset it?

Will keep an eye anyway in case it happens again.

 

[coolypops]

I doubt that would cause it, but maybe...

Hope it doesn't happen again, but it more than likely will.

On that mileage it's quite probable that it's soot buildup on the turbo vanes so it might be a good idea to give it a clean out anyway.
Or at least give the car a few hard runs to try and blow off as much buildup off as possible.

And a couple of other tips for improving/sustaining the motor are to either run the car on good fuel (Vpower, etc.) or use a fuel additive such as millers
and also to give the air intake and EGR(exhaust gas recirculation) valve a clean out as they get caked in carbon over time.

 

[Greggo]

This problem occured again yesterday - was pulling onto motorway from a roundabout and when i got to 5th gear the power went and couldnt get above 60 for ages.

Restarting and giving some welly on the gas seemed to do the trick. I havent got round to putting a full tankful of good fuel in recently cause ive been skint and I've only been able to afford asda fuel lol, but i bougt some redex on offer, so will try and get some quality fuel in on payday and give it a good clean out!

 

[onesh0t]

Happened to me the other day after a few weeks of town driving with little boost. I planted the car, because I was getting on an A road and after I got through 2nd gear - BAM! - limp mode

Gave the engine some heavy work under load and it's working like new again (132k).

 

[Greggo]

Yeah, I think my car doesnt seem to like it when I hardly use the boost, as when I do get chance to give it some, it stutters and then limp modes until I re-start and even then takes a few gradually increasing blasts in 2nd and 3rd gear to get it pulling as normal.

 

[jerryf70]

Another one to try

I'd add a 5) to the list above. Probably not very common but easy to check:

5) Pipe from N75 to turbo vane actuator holed

Happened to me because somebody had routed it wrongly at some point in the past and it had eventually melted on EGR (I think). Same symptoms as you describe, the only diagnostic message was "low boost". This made the turbo run at a lower boost than the management system was demanding, which in turn gave up and commanded "limp home" mode at random times (for me normally at 70 in top gear). Easy to check, just do a visual on it from N75 (top LHS of bulkhead as you look at it) down to the turbo.

Hope this helps