newb with a A4 1.9tdi and power problems

[daron]

Hiya,

i've just bought a 1.9tdi, it's a great car, and a bit of a step up from my usual bangers!

However it does suffer from the "power loss" problem - occasionaly the the power will drop off - it still runs smoothly and without any extra smoke or noise but it feel like its lost the turbo?

The guy i bought it off said that he had had this problem, replaced the MAF sensor and that had sorted it, he was advised at the time that it could also be the boost control valve

He told me that when the power does drop off, turning the ignition off and back on again whilst driving sorts the problem. I have tried this and it does work.

I know there may be many causes for a power loss problem, but does the fact that i can cure it by turning the ignition off and on again help to diagnose what and where the problem may be?

Thanks for reading this

D

[ini]

Is your car the 110 version?

Does the powerloss occur under load on hills or on the motorway, in third gear and above at around 3000rpm?

Could be a few things, but generally it is a sticky turbo VNT mechanism on the 110's (sooted up turbo internal wastegate). This can be cleaned in a few ways.

Failing that it could be a worn MAF, or N75 boost control valve, or leak in a control tube.

[daron]

that was a quick reply!!

Yeah, its the 110

To be honest i've not driven the car enough to say for definate what condition the fault occurs under, i would say that it's not just happening at hills

Why would turining the ignition on and off, whilst driving, cure the problem as it does? (i'm not that clever when it comes to cars!)

I'll do a search on here for how to clean the "vnt mechanism"

Cheers

D

[avspider]

Is your car the 110 version?

Does the powerloss occur under load on hills or on the motorway, in third gear and above at around 3000rpm?

Could be a few things, but generally it is a sticky turbo VNT mechanism on the 110's (sooted up turbo internal wastegate). This can be cleaned in a few ways.

Failing that it could be a worn MAF, or N75 boost control valve, or leak in a control tube.

here we go again....

[ini]

Big breath.....

If the car detects an engine parameter which has a large difference from that expected, (in this case the boost pressure is most likely out of range, and is much higher or much lower than expected) it puts the engine into 'limp mode'.

This is a safety precaution that reduces fueling, rev's and boost pressure, limiting possible engine damage incase something major has gone wrong, and still allowing you to drive to a garage.

A VNT turbo has a number of small pivoting aerofoils around the turbine, which regulate boost by altering the angle that the exhaust flow hits the blades and changing the 'aspect ratio' of the internal geometry. This helps to eliminate lag at low engine speeds and regulates boost faster/more efficiently than an external wastegate.

On cars that are mainly used to make short journeys, the variable geometry mechanism can become jammed up with crud, and instead of the vanes pivoting smoothly, they start to stick, mainly they stick in a 'high boost' semi closed position, never opening far enough at high rpm.

The car see's the 'overboost' or 'underboost' as deviating from the range expected in the ECU MAP's, and triggers 'limp mode'.

Cycling the key in the ignition cures the problem, as 'limp mode' is generally only a temporary measure.

It may not be a 'sticky' vnt mechanism, as problems with the N75 control valve, vacuum control tube leaks, defective MAP pressure sensor, and a failing MAF can all cause the same 'pressure difference'.

[daron]

Thanks for all your input with this,
It's great to be able to ask experienced experts about a problem and get a detailed, informative response!

cheers

D

[SS069]

mine too is underpowered, but as ini says, could be a few things, I'm gradually working my way through what it could be.

Messed with the EGR yesterday, but made no big difference, so going to replace a few of the vacuum pipes to the turbo actuator & the EGR to see if that makes any difference.

I'm wondering if it could be the pressure control valves for either the EGR, turbo actuator or both - are these a common failure ?

The next step after the above would be to go down the MAF route, but mine smokes alot under heavy acceleration.

How do we clean the variable geometry mechanism ? - I have read it somewhere on here, but cant find it again......:confused:

[SS069]

found the turbo cleaning thread - Mr Muscle foam oven cleaner squirted into the turbo once the cat pipe has been removed & then play with the actuator arm for an hour or so & then give it a general clean out............;)

[daron]

SS069 - did you notice an improvment after the clean out? i'm assuming from the ";)" that you had some success?

[SS069]

SS069 - did you notice an improvment after the clean out? i'm assuming from the ";)" that you had some success?

Just cleaned the turbo with Mr Muscle as suggested & checked all the vac pipes, built everything back up as it was/should be, but there was no noticeable difference..........

Just been out in the car this afternoon & done approx 260 miles in the car - the turbo is trying to boost, but pushed lots of soot (black smoke) out of the exhaust.

The turbo appears to be coming back to life, so I'm going to run the car for a while to see if the power improves - the car is rather economical as it is though ;)

[daron]

I've not done anything about this problem with my audi - i've just been using the "turn the ignition off and on again" trick for the last few months. I've just been searching around about this problem and found a link to this "Inotec turbo cleaner" - has anyone tried this?

D

[chillin_uk]

Think im having exactly the same problems, black smoke under heavy acceleration, and loss of power sometimes, the key trick works for me aswell,
Im not able to do the work on car myself, so anyone got any idea how much i could expect to pay for the diffrent parts it could be or what i should try first? thanks..

[john davis 100]

Hi
I have had this problem for about 2 months but without the black smoke, I have changed the MAF sensor,N75 valve,pipes and the ECU and if my mechaic had done what these guys suggested and just cleaned out the turbo as I asked,I would be a lot better off both financially and mentally!!
I am going to have a go at the cleaning job at the weekend and I hope this cures it,so fingers crossed and I will let you know,however someone did suggest loading the car up with 4 adults and a boot full of luggage and giving it a really good run to get the exhaust hot and it may reak down the carbon.I will keep you posted.

[steeevo]

i had that with the black smoke only when i accelerated and it felt like the turbo had broke, my mechanic found it to be a split turbo pipe? he replaced it and it was good as new.