Hello All,

I have been working with my new 2004 A4 Quatro 1.8T and have been experimenting with Vag Com. I have recently tuned up the vehicle in trying to get the fuel economy up to near 30 mpg on highway driving. I researched things on the forums and have done the normal things like cleaned MAF, AIT, replaced oxygen sensor, checked for leaks, seafoam.

I recently noticed that the requested boost vs. actual boost are not matching during normal driving on the highway. Is this normal? when not requesting boost or in small loads the actual boost is always much higher while logging block 115. See the attached chart with an example of normal highway driving.

Also - the multiplicative fuel trim on block 32 has always been high at around 8% to 12%. I believe this means the O2 sensor shows a lean condition and the fuel trim makes the system more rich to compensate.

I have a theory that this may be causing my reduced fuel economy due to the common use of turbo boost (and more fuel) when not really being requested by the driver/ECU.

Can anyone confirm this theory or suggest any other ideas? Also, what would cause the actual boost to be higher then requested? When I push the car the requested and actual seem to come together

 

when u say u played with VagCom, did u do anything with it? or just log'ed it?
i get like 24 miles per gallon on a hwy.

 

I logged all the normal channels to check out the engine. I also did the throttle body adaptation after cleaning it. My car is getting about the same at 24 mpg with stock everything. I was expecting the car to get around 30+ mpg based upon the EPA estimates and the reviews from others.

My question relates to whether it is normal for the car to have higher boost then the ECU is requesting at medium throttle levels. This is shown in the boost graph I uploaded in the original post. This shows the ECU is not requesting boost but when the car has medium load levels but the actual boost is around 300 mbar

I am wondering if the boost control valve (which I think is the N75 valve) could be causing this issue. I have not checked this part and hoses yet.

I wanted to make sure the car was working well before getting the ECU chipped with APR stage 1.

Any ideas or comments on the normal turbo boost requested vs. actual at normal highway driving levels would be appreciated.