Power loss/limp problems. Please help meeee!!

**Bodevo** · 28-08-2018,04:41 PM

Hi all
I am hoping you clever people will be able to help me, please.
I know this is a subject discussed at length and I have searched, read and tried all sorts of suggestions but can’t seem to get to the bottom of it.
I have 2003 VW B5.5 1.9tdi 130 (AVF engine) auto.
First had intermittent power loss/limp mode then after a few days became permanent.
Diagnostic code showing as 17964 - Charge pressure control; negative deviation – permanent.
I have changed the Solenoid Valve for Boost Pressure Control (N75), no difference.
Checked all vacuum hoses, replaced a couple of suspect ones and am pretty sure I have no leaks and all correctly connected.
Vac pump pulling plenty out (-23/24 inHG ((-600 mmHg))
VNT seems free and seems to operate normally. (Fully up on idle then moves up and down when revved up).
Have read that sometimes the VNT gets carboned up and needs removing to clean but the lever seems to operate freely.
Really scratching my head now.

Any suggestions very much appreciated.
Cheers
Nigel

**Bodevo** · 01-09-2018,03:08 PM

OK just to update in case anyone would like to help me.
Just changed MAF and that has made no difference.
Help me plzzzzz
Thanks
Nigel

**Rob69** · 01-09-2018,04:26 PM

It could be the manifold boost pressure sensor but more than likely to be the VNT gummed up or sticky, when you see it operating visually by revving the engine there is no load on the engine, once it is driving along, loaded up with the turbo red hot and actually doing some work I suspect the movement is not as smooth or complete as it seems. if you can get vcds and run live data while driving you can compare boost required to boost actual and this would prove the vnt operation.
Good luck - stick with the B5 if you can, difficult to find something to replace it with, as I've recently found!!

**Bodevo** · 01-09-2018,04:45 PM

Ok thanks for that Rob.
I dont have access to a vcds, just a dephi diagnostic but I cant see a measurement for turbo boost on it.
I will give the mr Muscle thing a try and see if that helps. The only problem I see with the diagnosis of the vnt is that when it first did it I switched the ignition off and back on and it cleared. Would it do that if the vnt was sticking? Now it is permanent. I have code 17964 - Charge pressure control; negative deviation - Permanent. I clear it then drive and it comes back. Before I clear it the vnt control rod doesnt move, when I clear it or turn ign off and on again it does move.
I really like my B5 I have to say, had very few problems with her up until now. Although she has nearly 300k km on her she normally runs great and uses very little oil.
Thanks again for your input
cheers, Nigel

**A55** · 01-09-2018,08:28 PM

17964 - Charge pressure control; negative deviation, looks like its taking too long to reach requested boost-which is causing your limp mode, any leaks in the pipe work-from turbo to manifold ??? not always easy to see but when driving have you heard any whistling ??? or weeps of oil from intercooler ?? had same prob-limp key of then on it came back on boost, them limp again, turns out that intercooler was leaking-just a tinny weep of oil from corner it was quite old tho, failing that sticky vains on turbo would be next best bet !! since you have checked the vac lines an they ok -23/24 inHG on the vac gage seems high tho- usualy fully open by 17-18, and starts to open at 3-5 that said tho if it was ok before then that must just be how it was set--unless vains are sticking and thats why its taking so much vac to operate it ?? just a thought !!

**Bodevo** · 02-09-2018,12:05 PM

Thanks for that.
I can hear a very faint hiss on acceleration but not when I rev the car when stationary.
I think I am going to have to look more closely at the intercooler and pipes. I replaced a split booster pipe a few months ago (the one from the bottom of the turbo). I will investigate further.
Thanks again
Nigel

**A55** · 02-09-2018,12:47 PM

you wouldnt hear that much of a leak just reving unless it was a big one-as it not under load so no great build up of pressure. A faint hiss dont realy sound that much to worry about (you can usualy hear some turbo-air noise anyway-but it just could be enough of a leak to cause slow build up of boost giving you limp mode. Have you def checked all vac pipes ??? one small leak would allso cause slow to activate turbo giving slow uptoo boost then limp !!!

**Bodevo** · 02-09-2018,01:14 PM

OK thanks again.
I have used a vacuum pump on all the vac pipes and they all seem to hold the vac but I think I will get some new silicone vac pipe and replace the lot to be on the safe side. The faint hiss is something that wasnt there before (I dont think)
cheers
Nigel

**A55** · 02-09-2018,01:32 PM

Other places to check (since you think Hiss not there b4)-look at- feel-under inlet manifold for weeps of oil-not sure on the setup of your car-ie-dose it have the plastic pipe running along the underneeth of the rad going to intercooler ? I'v seen them get cracked and it not realy show drips of oil unless it very bad.

**Bodevo** · 02-09-2018,01:36 PM

Actually there is a little bit of oil under inlet manifold. I noticed it smoking bit the other day when it was hot. I thought it was coming from the egr. Where could that be coming from? Difficult to see for the egr though.
cheers
Nigel