Upgrade Work

Even more perplexed

To recap:  I began by doing some pulls to check out a new software tune and verify the calibration on some pressure sensors was correct.  During a third gear pull something went wrong and the wastegate duty cycle dropped to zero and the tone of the vehicle changed.

I found a wideband O2 sensor plug had come out of the downpipe changing the tone but I still couldn’t figure out why the boost had dropped so suddenly:

event_boost_log

I was able to determine that the sensors were generally within 1 psi of the vehicle map sensor – shown above.

I disconnected the compressor signal lines from the N75, separated the individual lines from the tee, and attached a sensor to each line to monitor the pressure in the housings independently.  Those results were not good, one K03 was boosting to almost 25 psi and the other not at all.

compressor_comparison

I started the disassembly process to try and find the source of the problem.  After looking in the charge pipe and exhaust pipe I moved onto taking the motor out to inspect the turbocharger.  After taking it off I cannot find anything wrong with it.

BorgWarner K03 Turbocharger
BorgWarner K03 Turbocharger

I’m thinking of having it rebuilt just for the sake of it, ‘while I’m in there’, and if I do will send this ones partner along with it for the service as well.

brother_k03

Turbocharger

Still digging for answers

After pulling off the passenger side intercooler the charge pipe coming off the compressor housing looks fine:

clean_outlet_pipe

And looking at the catalytic converter for the passenger side it’s looking fine as well:

clean_catNext up is the motor coming out so that I can visually inspect the passenger side turbocharger.

 

Testing

That’s not good

While driving the other night I heard a bang sound followed by a drop in power.  Subsequent the car sounded a bit different.  Initial investigation showed that one of the two wideband O2 sensor bung plugs in the downpipe had come out.

That plug coming out seemed like an odd cause for dropping power so I continued to investigate.  An intake pressure check was good, I tested the wastegate lines and they were good.  When the car was idling there was no smoke or visible water vapor coming from the tail pipe.

I was still suspicious of a possible turbo problem so I hooked up separate pressure sensors to each compressor housing signal line and then went out to record the pressure in the turbo compressor housing.

compressor_comparison

The results are shown above.  The great disparity between the driver side and the passenger side (driver side is blue and passenger side gray), and neither matching the MAP sensor, has me concerned that the passenger side turbo may have failed.

Audi B5 S4 Information and Testing