Over/sluggish boost problem - vagcom logs attached

[Froggy_130]

Hi All,

I'd be really grateful if you could help me with a boost problem I am having at the moment.

Car is a 2001 Passat 130 PD, engine code AVF, kerma/alligator tune.

The car has gone into limp mode a couple of times with the error 17965 - Charge Pressure Control: Positive Deviation, graphing actual versus specified boost shows the actual is quite sluggish to follow specified particularly coming off boost. I've graphed a run this morning here:

http://www.mediafire.com/?mjrzkmri15y

It's an Excel spreadsheet, I did try to use google spreadsheets to make things easier but the graphing isn't up to much!

Yellow line is specified boost, light blue is actual boost. Duty cycle is dark purple.

Notice quite a scary boost spike at around 540 seconds!! Also whenever I come off boost/slow down or at idle specified can take a long time to get back to actual - i.e. a good example in the graph between 640 and 670 seconds!

I guess prime suspects are worn vac lines, faulty map sensor, N75 valve or stuck VNT vanes. I've replaced most of the vac lines and have a new map sensor but it hasn't made any difference. I'm not convinced about stuck VNT vanes as actuator movement is smooth over about 2 cms, and if I pull the vacuum hose whilst coming off boost the boost immediately drops.

Do you think next step is the N75 valve?

Its only recently started to do this by the way, has been fine with this tune for nearly 2 years now. I have noticed recently mpg has dropped a fair bit (I know it usually does over winter but this seems a significantly bigger drop than usual), and the turbo whistle has seemed a lot louder lately - maybe a leak somewhere but would this cause over/sluggish boost? Performance is top notch as ever, still pulls like a beast!!

Again, really grateful for any help!

Cheers,
Dave.

[martin1810]

Watch the actuator when someone starts the car. Does it move 20mm. This means the vacuum part of the actuator is working and suggests that the N75 valve is working. You have changed the MAP sensor , so it shouldn't be that. Everything points to stuck vanes in the turbo. Seeing the actuator move, doesn't tell you anything about the turbo vanes. It is possible the N75 valve is stuck and cannot bleed off pressure. Another silly fault is a blocked pipe running from the N75 valve to the air filter. GIven the cost, I would change the N75 valve and then budget for removing and cleaning the turbo.

[Froggy_130]

Hi Martin, thanks for the input and apologies for the late reply - tinkering and surfing time is severely limited these days with a 5 month old baby

Changed the N75 and still got the same problem so I guess next step looks to be cleaning the vnt mechanism.

There is quite a long running thread on tdiclub.com that discusses cleaning the turbo chemically with no less than oven cleaner

http://forums.tdiclub.com/showthread.php?t=246287

Looks like it works in a similar way to innotec turbo cleaner, I guess I've got nothing to lose giving it a try!

One other thought I did have was whether a blocked cat could cause the problems I am seeing - poor mpg, turbo whistle much louder than usual, this morning it seemed to drive terrible with lumpy acceleration and lumpy when slowing down like something was holding it back. If I blip the accelerator at idle I hear the turbo whistle and actual boost rise quickly but take 2-3 seconds to drop back down... Anything I can do to check the cat? I did wonder about unhooking it from the turbo and blipping the accelerator a few times at idle - if the whistle/actual boost drops immediately then would this indicate a blocked cat?

Sorry for all the questions and appreciate any response!

Cheers,
Dave.

BTW in answer to the questions in your post the actuator does move about 20mm when the car starts, I've also replaced all pipes between the n75 valve and air filter so that isn't blocked.

[martin1810]

17965 is often due to stuck turbo vanes. If you don't mind some time and effort ( I know, baby), you can take the turbo off and clean it. It is only carbon so oven cleaner is ideal. There are a number of instructions on the web if you google. One particularly good set of instructions is from a guy doing a rover turbo. I wouldn't bother with trying to clean the turbo whilst on the car, but that's up to you. I doubt the problem is a blocked cat. That really is quite a rare event and I can't see it producing the 17965 code.

[cazyp]

Mine is a taxi and over time with lots of city slow snail like driving I get 17965.
I have cleared it twice now by filling an almost empty fuel tank with a bottle of Forte diesel treatment (approx £10) and £20 of Shell Vmax.
Drive it around until warm and take it for an italian motorway tune up. May drop into limp mode a couple of times over the first couple of days.

I done mine again a few weeks ago after a lot of slow driving in the snow and now running as good as new again over a 12 hour shift with little or no soot from exhaust and no limp mode.

Well worth a try before getting down and dirty with the turbo off (esp' with your limited time!)

[passat 130 tdi]

mine was the map sensor - HTH .

[Froggy_130]

Thanks for all the replies guys.

passat 130 tdi - had a new MAP sensor (plus vac lines + N75!), made no difference unfortunately.

cazyp - tried a bottle of forte + £20 quid shell vmax last week (saw your post on another thread suggesting this!), been for a few blasts up the motorway in 4th but doesn't seem to have made much difference.

martin1810 - looking like turbo off is the way to go then, ah well! Got a weeks leave booked soon so I'll set aside a couple of days for it. Any idea if it is possible to remove without moving the front lock carrier into the service position?

I'll let you know how I get on!

Cheers,
Dave.

[martin1810]

You don't need service position. Most important thing is make sure turbo is full of oil when you put it back on and don't rev the engine for a couple of minutes to get the oil well circulated. It's basic nuts and bolts job. Just go slowly and take it easy.