Power Loss / Safe Mode? 2.5Tdi

[JamoJ]

After driving my 2.5Tdi Avant happily for several months, I'm now experiencing intermittant power loss, during said power loss the engine will not rev above 2800-3000 Rpm, even in neutral. The power loss lasts for an indeterminate amount of time and then clears.

No warning lights, not shuddering/juddering... nada... garage gave it a clean bill of health during last sevice two weeks ago.

Any ideas welcome as I'm stumped! :confused:

[drpellypo]

Check for fault codes first off as it could be a whole range of things. Mine recently did it and VCDS flagged up manifold problem which pointed to N75 failure or Sooted up Turbo. Replaced the N75 valve last night (£72 from Cheshire Audi) and it seems to be OK thus far. Will see how it is over the next few days.

[JamoJ]

Where about will I find the N75 valve?

[Crasher]

It is extremely unlikely to be a faulty N75 valve. Don’t go changing this first; you should do what drpellypo says and have a fault code read first. The symptoms sound like the turbo needs rebuilding.

[quattrogary]

This might sound silly but you might have water in your fuel.Highly unlikely,but it did happen to me a few years ago.If this is the case,she might smoke a bit when shes cold.

[drpellypo]

As crasher says the n75 valve went on mine but it's very very rare for this to happen. The parts guy at Audi said they had one in for two years and didn't sell it. It seems I struck the once in a blue moon statistic. If you put it on VCDS it should give you an indication of the problem. No amount of posting on forums is going to help you to be honest without a fault code because as you've already seen, the list of possible faults are endless.

[dan.taylor.1]

Id go for a few simple checks first, have the air and fuel filters been changed recently? as a blocked/water logged fuel filter could cause power loss like that say after a hard corner. simple check really before jumping in to codes and changing expensive bits!

[JamoJ]

Spent some time on this now, I've resited the urge to change the N75 valve... I've checked over the Vaccum pipes and the fuel has been used and re-filled since the fault appeared so I'm confident it is water and debris free (new filter during recent service). The problem has worstened now though and the car has finally reduced itself to more limp than leg and now the emission warning lamp is lit!

I dropped the car into VAG and asked them to do some diagnostics as I'm currently posted in Germany (The Cars mother land).... Fortunately I was sat down when they called. They want to replace the Turbo as the STARTING point! "are you flapping serious????" was my response.

Ya dat vill be oooh - two towzand euro Ya....

Crasher could well be right from the outset... turbo rebuild. However, the only diagnostic they seem to have performed is a boost pressure output test though. Surely there is more they can do? :(

[JamoJ]

Crasher could well be right from the outset... turbo rebuild. However, the only diagnostic they seem to have performed is a boost pressure output test though. Surely there is more they can do? :(

How much should I be looking to spend on a turbo rebuild? or a replacement exchange unit?

[accy]

For the last 3 days i have been lossing boost now and then

17957 control valve boost pressure - n75 open circuit / short with ground. p1549 intermittent

Would i be right in thinking a new n75 valve is required?

[Crasher]

I get the price of your turbo to be €1416.10 + 19% MwSt (VAT) and plus fitting which is relatively simple. Personally I would suggest taking it to a good recommended garage (there are not many dedicated independent VAG specialists in Germany as they are domestic cars and seen as run of the mill) who will have yours rebuilt for at least 1/2 of the cost of a new VAG unit. Reconditioning companies that spring to mind in Germany are BU (http://www.go4turbo.de/cms/front_content.php (http://www.go4turbo.de/cms/front_content.php)), BTS Bauer (http://www.btsturbo.de (http://www.btsturbo.de/)) and Motair (http://www.motair.de (http://www.motair.de/)) to name just three of many.

[Crasher]

For the last 3 days i have been lossing boost now and then

17957 control valve boost pressure - n75 open circuit / short with ground. p1549 intermittent

Would i be right in thinking a new n75 valve is required?

Which year and engine code?

[accy]

sorry should have mentioned this
A4 1.9tdi 130 bhp 2004
Also been remapped

[Crasher]

That will be either a broken/corroded wire or a faulty N75 valve. I would plug a new N75 in and hope the code clears, unless a wire to the N75 is obviously broken.

[accy]

Thanks for the reply crasher
Just rang audi for the n75 valve....They say that there are 2 n75 valves on my car and asked which one i wanted.
One near the turbo or one near the exhaust.

Would you know which one or even better the part number?
A4 1.9tdi 130bhp avf 2004

thanks

[Crasher]

There is actually only one N75 valve on the car but they will have done an SDC code search which brings up the wrong one in my opinion, you want the one that is on the bracket below the turbo on the side of the engine near the vacuum accumulator which I get as being 8E0 906 627 C. I think it will be a broken wire near the N75's plug.

[accy]

thanks for the advice crasher
Will buy/ install tomorrow

[accy]

Hi

Installed the new n75 valve ...the car drove great for a couple of days, but today lost boost again..no managment light on but did show codes

17957 control valve boost pressure - n75 open circuit / short with ground. p1549 intermittent

18027 glow plug relay (j52) openor short to ground

Surprised the glow plug relay always comes on as well when i lose boost..
Checked the n75 plug wires before replacing n75 and seemed ok

Any help would be appreciated

[Crasher]

Looks like a wiring fault.

[accy]

thanks crasher...would i assume the wiring fault be with the relay

[Crasher]

Not sure, nudge me later and I will follow the wiring diagram and see if I have any ideas.

[accy]

Hi Crasher

Drove home from work last night ....the engine light came on, following codes

17932----fuel pump relay
17996----engine mount solenoid valves (n144/145)

engine vibrates heavily at idle and when i turn the ignition off you can see the gearknob shaking

Brief history
Since iv had the car i have had the following codes

17932 (p1524)........fuel pump relay
18027 (p1619)........glow plug relay
17957 (p1549) boost pressure (n75)
17996 (p1588) engine mount solenoid

The fuel pump relay turned out to be a faulty wire (fixed) thanks to your helpful advice.

The boost pressue n75 vavle was replaced.

Do you think all these faults are connected? maybe wiring?

Really surprised to see the fuel pump relay fault show its ugly head again.

[Crasher]

PM me the cars reg number please.

[Crasher]

Accy, theN75 and N144 are on the same fuse (228) but a fault with the supply to these would lead me to expect an EGR solenoid, brake and clutch switch, hall sender G40 and N239 anti shudder flap solenoid error codes. I would start by opening up the plenum chamber electronics box and checking for water damage

[accy]

Thanks for the help/advice Crasher always appreciated

Will check the plenum chamber electronics box for water damage

Would i be right in thinking the engine mounts are hydraulic ?
Can't help but thing with the engine heavily vibrating (most of the time) it is some how putting stress on wire connectors possibly linked to the faults im getting

[Crasher]

Only the mount on the cars left hand side is electro hydraulic.

[JamoJ]

I get the price of your turbo to be €1416.10 + 19% MwSt (VAT) and plus fitting which is relatively simple. Personally I would suggest taking it to a good recommended garage (there are not many dedicated independent VAG specialists in Germany as they are domestic cars and seen as run of the mill) who will have yours rebuilt for at least 1/2 of the cost of a new VAG unit. Reconditioning companies that spring to mind in Germany are BU (http://www.go4turbo.de/cms/front_content.php (http://www.go4turbo.de/cms/front_content.php)), BTS Bauer (http://www.btsturbo.de (http://www.btsturbo.de/)) and Motair (http://www.motair.de (http://www.motair.de/)) to name just three of many.

Crasher,
Thanks for the direction... as it happens I've found a local independant that has been able to replace the turbo with new at a slightly lower than extortionate price. The sago continues as it's made no appreciable difference to the cars performance.

Currently running 16.3 horses instead of 163! Getting dis-heartened now as I'm in the middle of Germany surrounded by VAG agents on home ground that can't identify the fault. If you can suggest anything else I'd be extemely grateful!

JamoJ

[Crasher]

It reminds me of one I did that had six blocked injectors, I have no idea how all six became blocked but I took them to a local diesel specialist who is very good and he fitted new nozzles and this transformed the performance. Other possibilities are a faulty Air Mass Meter and the cams could be worn depending on the year and engine code, what is it?

[JamoJ]

Its a late 2004 (54), not sure of the engine code... BDG? WAUZZZ8E05A079525

[Crasher]

A 2005 model with a BDG engine, try a new Air Mass Meter first, genuine Audi ONLY!

[JamoJ]

At last I've found someone with VAG-COM .... ooorah. It's owned by a Polish guy and is operating in German but the vital numbers are the same. Low and behold, N18 Valve giving some strange readings at full throttle and the Air Mass Meter is giving readings that would suggest that it's sha***d. Both ordered today and arrive tomorrow, to be fitted instantly. Will update on the results!

Let there be light...

[JamoJ]

Ok, new turbo (VW's idea) new air mass meter, new n75 valve and n18 valve... and... no change! Getting threaders now. Have checked the vacuum system pipes for correct connections, all appears ok. Where does the vacuum pipe go that disappears under the NSF wing?

Tick over is approx 40rpm low, air pressure output from the air mass meter is low, the turbo output pressure is low (and only reaches half of expected value at full throttle at best), Cat has been checked by VW and given a green light, vacuum is good. The car will tick over lovely and will reach full throttle without load... albeit slowly, under load the acceleration is very sluggish (ie no turbo assistance) the economy reflects this (approx 28mpg when it used to do approx 40).

Any ideas welcomed. Even the German VW guys are scratching their heads now!

[JamoJ]

Another update... had a look at the old turbo, it appears the seal has been blowing through quite a lot of oil, and guess what... the CAT is completely ruined giving too much back pressure. The Lambda sensor is also completely goosed. So, new turbo, new CAT, new Lambda sensor, new n75, new n18 valve and a new MAF. Should get the car back this week. After paying for this little lot though... I can't afford the fappin fuel!!

Thanks to everyone that had some useful input!

[Crasher]

Lambda sensor? What lambda sensor?

[machinedred]

ihas this been resolved ? mine does this too , i think its the auto box putting the engine into limp ??!! either way its frustrating