TDI 75 not warming up and losing power

L

LordTJC

Member
I’m having two issues with my 2001 TDI A2 currently that may or may not be linked.

1. The temperature never gets above 70 degrees on the gauge. I have changed the thermostat and nothing appears to have changed.

2. Under hard acceleration, there is a sudden loss of power. It feels like the turbo is being switched off. I believe it is going into limp mode? Stopping and starting the engine appears to fix the broblem until accelerating hard again.

I’ve searched and found others that have had similar problems. I will be getting the car vault scanned soon and report back. Until then, any suggestions of what might be the cause(s)?

Thanks
Tim
 
1. Have you changed or checked the temp sender.
2. Fuel filter causes similar issues, when was it last changed.
 
As above

1. Fuel temperature sender
2. Likely to be a boost leak on one of the pipes or intercooler
 
Just got back from having the car scanned. Relevant fault codes as below:

17571
Fuel temperature sensor
Faulty signal

17664
Coolant temperature sensor
Interruption/Short circuit to positive

17965
Boost Pressure
Intake pipe pressure too high

I think my next step will be to replace both of the temperature sensors. When revved we discovered that the turbo actuator is not working and there is no vacuum in the pipe that activates it. We think there is a leak somewhere in the system.

Tim
 
I’m going to try and check for any leaks in the pipes. Can anyone explain which ones I’m supposed to check?
 
To follow this up, recently the temperature gauge has been upto 90 and stayed there on a couple of long journeys (1 hour). On short journeys (about 20 mins), it gets to about 70. I think it may be worth changing the sensors that are on the fault scan anyway.

I'm still having limp mode problems. I can hear turbo noises when driving at low speed with the windows down, but I can't tell if its normal or not?
 
For the hoses you need to check, there's the vacuum hose connections diagram here which should give you a good start. There's a good chance that the issue is the intercooler located at the front of the car, driver's side (assuming UK) next to the radiator - forum members have indicated that they are prone to failure.

Replacing the coolant temp sensor is a bit of pain but doable by anyone with the time. Not sure about the fuel sensor.
 
The 17965 fault suggests the limp mode is caused by too high a boost pressure - in other words the wastegate isn't opening properly. A leaky intercooler would cause a loss of boost pressure so I think part of your problems are likely to be the vacuum pipes either mis-connected or leaking preventing the wastegate from opening.

Simon.
 
Thanks for the advice. I had a look at the pipes while doing the service but couldn’t see anything untoward. I’m going to try and change the N75 valve before giving up and sending the car to a garage. I can’t find one on Euro car parts. Anyone know where I can get one from?

Thanks.
Tim
 
I just fixed my limp mode issue and it was as simple as re-connecting a little pipe coming from the N75 valve back to the turbo housing.
I say "simple", but it was difficult to see as a visual check and to get at but it's worth checking that.
See here:-

limp mode after aggressive acceleration

OK, after re-setting the codes and a short gentle drive - no fault codes appeared on an autoscan. After another drive where I accelerated hard up a hill and the power dropped I got:- 17965 - Charge Pressure Control: Positive Deviation P1557 - 35-00- - Sorry about the red herring of the...
a2oc.net
 
LordTJC said:
To follow this up, recently the temperature gauge has been upto 90 and stayed there on a couple of long journeys (1 hour). On short journeys (about 20 mins), it gets to about 70. I think it may be worth changing the sensors that are on the fault scan anyway.

I'm still having limp mode problems. I can hear turbo noises when driving at low speed with the windows down, but I can't tell if its normal or not?
Click to expand...
My 2000/2001 AMF engine turbo wastegate was seized at the pivot point this was cleaned & polished with scotch Brite pad & then relubricated with high temperature grease before reassembly.

Keith
 
The thermal efficiency of the tdi lump is well known. The one area where is bleeds heat is the turbo, the lubrication dries out bearing surfaces rub and as Keith said pivot pins seize up and wastegates "fail". To make things worse the turbo is not very accessible for routine maintenance. I would even say very few even think about it until there is some sort of issue. Got to be worth trying Keiths @kp 115 clean / lube repair.
 
LordTJC said:
Thanks for the advice. I had a look at the pipes while doing the service but couldn’t see anything untoward. I’m going to try and change the N75 valve before giving up and sending the car to a garage. I can’t find one on Euro car parts. Anyone know where I can get one from?

Thanks.
Tim
Click to expand...

Hi there, did yoy manage to sort the boost issue?
 
Abe123 said:
Hi there, did yoy manage to sort the boost issue?
Click to expand...
Yes I did indeed. I thought I updated this thread when I got it sorted but obviously I didn’t.

I ordered a new N75 valve. When I went to remove the pipes from the existing valve I noticed the one on the top was just resting on the valve, not actually connected (see picture).

Couldn’t believe I never noticed it before. Even had my mechanic friend look over everything. I plugged the pipe in and all was fine. Cleared the codes with VCDS and no issues since. I suspect the pipe might have got pulled off while replacing my spring and top mount.

If your having the same issue it’s worth checking all the vacuum pipes that connect to the valve. If I remember correctly a couple of them go down the back of the engine. Very tight but I did get my arm down to check them (before I discovered the loose pipe at the top!).
 

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LordTJC said:
Yes I did indeed. I thought I updated this thread when I got it sorted but obviously I didn’t.

I ordered a new N75 valve. When I went to remove the pipes from the existing valve I noticed the one on the top was just resting on the valve, not actually connected (see picture).

Couldn’t believe I never noticed it before. Even had my mechanic friend look over everything. I plugged the pipe in and all was fine. Cleared the codes with VCDS and no issues since. I suspect the pipe might have got pulled off while replacing my spring and top mount.

If your having the same issue it’s worth checking all the vacuum pipes that connect to the valve. If I remember correctly a couple of them go down the back of the engine. Very tight but I did get my arm down to check them (before I discovered the loose pipe at the top!).
Click to expand...

Thanks! I have replaced my n75 valve with all pipes connect properly. I managed to take a photo of the turbo earlier.
 
LordTJC said:
Yes I did indeed. I thought I updated this thread when I got it sorted but obviously I didn’t.

I ordered a new N75 valve. When I went to remove the pipes from the existing valve I noticed the one on the top was just resting on the valve, not actually connected (see picture).

Couldn’t believe I never noticed it before. Even had my mechanic friend look over everything. I plugged the pipe in and all was fine. Cleared the codes with VCDS and no issues since. I suspect the pipe might have got pulled off while replacing my spring and top mount.

If your having the same issue it’s worth checking all the vacuum pipes that connect to the valve. If I remember correctly a couple of them go down the back of the engine. Very tight but I did get my arm down to check them (before I discovered the loose pipe at the top!).
Click to expand...
I think I’m right in saying the waste gate is operated by air pressure rather than vacuum to operate . (AMF 75)
Hth
Keith
 
kp 115 said:
I think I’m right in saying the waste gate is operated by air pressure rather than vacuum to operate .
Hth
Keith
Click to expand...

I will have to check any pipes from the wastegate at the top of the engine. Ive been reading and i have been having the exact same problem. Code 17965 boost fault.
 
Abe123 said:
I will have to check any pipes from the wastegate at the top of the engine. Ive been reading and i have been having the exact same problem. Code 17965 boost fault.
Click to expand...
I replaced all mine with new Audi vacuum hoses for guaranteed future performance & piece of mind.
Hth
Keith
 
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