A4 1.9 TDI Motorway Speed Limp Mode

[inigoj]

Recently my 97 A4 TDI 110 has started to go into limp mode when accelerating over 80mph.

There are no problems accelerating uphill etc at lower speeds, just seems to be 5th gear?

I have just been checking all the hoses and found that the small diameter tube from the inlet manifold to ECU pressure sensor was full of liquid. Could this affect anything?

I have already changed my maf and boost N75.

 

[Caesium]

If the engine went into limp you'd only be able to do about 15-20mph.
the liquid in this tube, what was it? whatever it was, its certainly not right.

 

[inigoj]

When i say 'limp mode' i mean it is overboosting and shutting off the turbo.

It will still accelerate but just as a non-turbo lump.

Cycling ignition does reset it.

 

[Mcgough]

Recently my 97 A4 TDI 110 has started to go into limp mode when accelerating over 80mph.

There are no problems accelerating uphill etc at lower speeds, just seems to be 5th gear?

I have just been checking all the hoses and found that the small diameter tube from the inlet manifold to ECU pressure sensor was full of liquid. Could this affect anything?

I have already changed my maf and boost N75.

yea my last 130 Q did this when accelerating past 100mph, at exactly 100 it would go into limp mode,

it went back to audi several times, they changed the Maf, the valve, then re-programmed Ecu, finally replaced Ecu, then eventually found the vane was sticking open on turbo, so they replaced it had no bother after that.

you still under warrenty??

 

[Caesium]

then eventually found the vane was sticking open on turbo, so they replaced it had no bother after that.

Do you mean Wastegate?

 

[Mcgough]

?????i got told Turbo Vane?? thats audi for you make special names up

 

[mattc83]

the tdi have a varable vain turbo. bascally it is little flaps in the exshaust section of the turbo. they move to alter the angle of flow on turbine blades to reduce turbo lag

 

[Mcgough]

.......thats the little buggers!!

 

[Caesium]

I have seen what you mean now, they're lots of small vanes that adjust angle to control flow of exhaust gas onto the turbine blades. This technology does not need a wastgate.

I'll hold up my hands and say I have never seen this in a turbo, but then again I've only ever had the turbo on a petrol engine apart, and apparently this technology is rare on petrol.

See here http://www.autozine.org/technical_school/engine/tech_engine_3.htm#VTG

 

[inigoj]

After towing a car on a very heavy twin axle trailer 500 miles today, my overboosting problem has vanished.

Infact my car seems more powerful than it did when i first bought it, accelerates well, right through to 5k, pedal to the metal in every gear.

Does this mean that the problem was a sticky VNT mechanism?

 

[Mcgough]

...possibly. but possibly not apparently mine was sticking in the max/open position which made the car overboost while changing from 4th to 5th.

possibly you had a diff problem which, now with a bit of italian tune, you have rectified!!!