Limp mode after 60 mph???

[tdiestate]

Hi all,

I have a superb tdi pd100, 2004 as a taxi

Drives fine around town turbo comes in no problem, soon as you go over 60 it knocks into limp mode, restarting the ignition takes it off again and sometimes after that it will go over 60. vag com brings up:

17964 charge pressure control, negative deviation p1556-35-10 intermittent

the engine management light comes on when it happens but a bit more urban driving turns it back off again

I've unplugged the MAF sensor as per some other posts but that brings the limp mode in at 50!!!

Its an AVB engine if thats any help

Any help would be much appreciated!

[rotodiesel]

Probably sticking VNT vanes in the turbocharger, leaking vac pipes or possibly N75. As a rough and ready VNT check (quite effective though):

Disconnect vac pipe to VNT actuator, fit a length of tubing and suck hard. Feel underneath for the actuator rod and check that with strong mouth vacuum it moves smoothly about 20mm. Put your tongue over the pipe and check that it holds vac - ie doesn't move back. Then release vacuum and check for smooth return. Finally blow down pipe and check that the actuator rod does not move, ie. it's on its stop.

If the VNT is sticking it can be freed off. Don't fit a new turbocharger.

How many miles has it done, how often do you change the air cleaner element and has it ever been overfilled with engine oil? (I'm investigating VNT stiction for another job - non VAG).

rotodiesel.

Edited 24 November, 2008 by rotodiesel

[Supurbia]

Do they actually go into limp mode? I notice no difference when I've had eml showing.

[rotodiesel]

If they ever see overboost they go into limp mode to safeguard the engine.

rotodiesel.

[tdiestate]

Hi there a bit more info:

the car has done 150,000 miles and is regularly serviced, i will try the pipe on the actuator soon as i get time, could that mean a leaking diaphragm??

i can get the car past 60 without going into limp mode by really revving it through the gears, but not a good look with passengers:D

[Lukey1965]

Hi, Had the same symptoms on my Mondeo TDCI recently (taxi as well !!). Changing the fuel filter cured the problem.

[Taxi 219]

A cheap easy result there

[tdiestate]

just to update:

Tried moving the actuator with some pipe, seems to hold its pressure ok, havent done the fuel filter yet! many thanks