Help is needed on this one.
Car 1996 A4, 200K miles, ran great uptil now.
While driving from LA to San Diego, code appeared.
Car was hesitating at high RPM, almost stalling out.

Here is what I have done so far:

1/ Replaced plugs - Bosch Platinum.
2/ Replaced O2 sensors - they checked out OK electrically but were very slow to respond so I changed the pre-cat plugs. Due to cost used the Bosch universal option.
3/ EGR - checked and verified correct operation
4/ Change over manifold - replaced, original part was damaged and leaking vacuum.
5/ Checked vacuum circuits, verified that I do have vacuum and not leaks - 15"Hg
6/ Replaced intake manifold gasket seals - possible root cause suggested by Audi mechanic when I left the car in for inspection
7/ Replaced fuel filter
8/ Replaced fuel injector o-rings
9/ Verified fuel regulator o-rings and seals

I have been working on the fir about 6 weeks and still no resolution.
When I check the car out after completing work it runs fine, when I drive at low speed it runs fine. I still have the codes and hesitation problem at high speed. I am looking for any information from some one who has dealt with a similar problem. Thanks

 

Replying for the record.
Installed a fuel pressure gauge to test if the O2 lean condition was caused by fuel starvation.
Test Results:
1 On starting car fuel pressure <5psi. Fuel line is empty.
2 Running at low speed fuel pressure is 30 to 40psi. Enough fuel gets to the engine to run.
3 At high RPM (3-4k) there is a small gain in pressure to 50psi and the engine runs for a while. After a short time the pressure drops to almost 0psi and the engine is fuel starved.

Conclusion:
Obtained replacement fuel pump and installed. Instal time <1 hour. Needed replacement hose clamps (5/8"). Replacement pump cost $140 at Vee Parts (San Diego).

Lesson Learned:
Fuel pressure is a key requirement to avoid lean burn.
ECM does not monitor fuel pressure.
Fuel pressure not listed on the fault tree I was using.


to make sure O2 lean burn was not caused by fuel starvation.
Testing showed that starting problem was due to low pressure (5psi) so the fuel was not getting to the engine. Hesitation problem at high speed was due to fuel pressure drop also. Work around: take foot off the gas, when RPM drops to 1k fuel will start to flow again.
Hesitation was due to pressure drop at high RPM