2008 Q7 4.2 TDI V8 Limp mode on hard acceleration after engine warms up

[Audi rocks]

Hi all

We are hoping someone can assist with this issue that occurs on hard acceleration / load but only after the car is driven for some time and the engine has reached operating temperature.

The limp mode is quite dramatic as car can still be driven but has very limited throttle response and sound of engine changes as if the timing is then retarded.

Car has DPF delete with stage 1 tune to ECU. No error codes being thrown.

Have cleaned the MAFs and disconnected the MAF sensors and it appears the engine then uses a set of default air flow values. The check engine light comes on and the engine performance appears restricted. The engine doesn't have the same acceleration and performance that it normally does but there is no limp mode as above.

People often talk of overboost causing limp mode. From what I can tell overboost does not throw error codes?

I understand this car has VNT turbos with actuators that are controlled by electric cable from ECU?

I also don't understand why the engine will pull great without issue until the engine reaches operating temperature. Does the ECU in some sort of safety measure limit boost or fuel until the engine reaches operating temperature and that is why we only possibly get issue when operating temperature is reached? Or is the temperature aspect mean something else is at play such as transmission? Or electrical sensor becoming problematic with heat?

Any help appreciated, thanks.

Hi in answring just in case you dident solve what i think is probably same probkem , in my case removing the catalitic converter interior as well as dpf solve the imparable values from maf sensors due to backpressure no egr as well , runs perfect since them.. cheers Mate hope it helps anibody

 

[Ulzyrakh]

I think I can remember that the problem came from the swapped diesel supply lines and return lines.

Wow. Maybe I’m connected lines wrong. Can you show me picture?

 

[tdi_my live]

Wow. Maybe I’m connected lines wrong. Can you show me picture?

No, unfortunately I don't have any pictures. At that time I had email contact with Big Lebowski and he had written to me that he had found the error because the lines had been mixed up.

 

[Ulzyrakh]

Hi all

We are hoping someone can assist with this issue that occurs on hard acceleration / load but only after the car is driven for some time and the engine has reached operating temperature.

The limp mode is quite dramatic as car can still be driven but has very limited throttle response and sound of engine changes as if the timing is then retarded.

Car has DPF delete with stage 1 tune to ECU. No error codes being thrown.

Have cleaned the MAFs and disconnected the MAF sensors and it appears the engine then uses a set of default air flow values. The check engine light comes on and the engine performance appears restricted. The engine doesn't have the same acceleration and performance that it normally does but there is no limp mode as above.

People often talk of overboost causing limp mode. From what I can tell overboost does not throw error codes?

I understand this car has VNT turbos with actuators that are controlled by electric cable from ECU?

I also don't understand why the engine will pull great without issue until the engine reaches operating temperature. Does the ECU in some sort of safety measure limit boost or fuel until the engine reaches operating temperature and that is why we only possibly get issue when operating temperature is reached? Or is the temperature aspect mean something else is at play such as transmission? Or electrical sensor becoming problematic with heat?

Any help appreciated, thanks.

Hello Big Lebowski. Can I contact with you by email? I want to share my car logs. I have limp mode problem. Still did not sorted. Audi A8 4.2 TDI 2010.
ulziibadrakh.e@gmail.com