If my car is burning oil inside the engine with fuel ... ?

[cparke]

INTRO: My car (98 Audi A4 V6 - AHA - 123000 miles) has been running rich for some time now with an abnormal fuel trim and throwing the following fault code:

17535 - Fuel Trim; Bank 1 (Mult): System too Rich
P1127 - 35-00 - -

The fuel trim values creep up on both banks each day until the CEL finally lights and learning stops until the ECU is reset. Bank 1 is always consistently much higher than Bank 2. Here is a snapshot of my current fuel trim:

Measuring block group 32:
O2S control learning values (before Cat. Conv.) [B=Bank S=Sensor]
-4.7 % @idle B1S1 +/-10%
-16.3 % @part B1S1 +/-10%
-3.7 % @idle B2S1 +/-10%
-8.2 % @part B2S1 +/-10%

I have been unable to resolve this issue with the usual tests & fixes: MAF, plugs, wires, coil, fuel filter, fuel injectors, fuel pressure regulator, camshaft position sensor, engine coolant temp. sensor, small vacuum lines, cleaning throttle body.

Having eliminated all these possible problems, I'm left with the theory that maybe the car is burning some engine oil with the fuel, and this results in the O2 sensors reporting less oxygen than expected and the ECU cuts fuel and causes the engine to actually run lean.

MY QUESTION: If the engine is actually burning oil with fuel, what would need to be done to fix that? Other than noticing white smoke in the exhaust (I really don't see any), is there a scientific method to check if this is happening? Are there several points of failure inside the engine that could cause this, or is there just one definite thing to check/fix to stop it? How much oil do I have to be losing to prove or eliminate the possibility that this is happening?

BTW - the car also has a small oil leak, and in 3 months it has lost almost a quart of oil. After driving the car and then parking it, oil burning smoke starts to rise from underneath the engine (more smoke coming up from under bank 2 than bank 1, but definitely coming up from under both banks), we think that is the oil starting to leak out onto the side of the hot engine as it settles down. It has been suggested that changing the valve covers should stop that leak. Could the same leak of oil to the exterior of the engine also be the source of oil getting into the engine to burn with the fuel?

Much appreciation for your thoughts, as always.

[Nebone]

That quart of oil missing might not be just from leaking oil but also from slight burning oil. You can perform a leak down test on bak 1 (driver side I believe) cylinders to diagnose the quality of your piston rings.

[cparke]

That quart of oil missing might not be just from leaking oil but also from slight burning oil. You can perform a leak down test on bak 1 (driver side I believe) cylinders to diagnose the quality of your piston rings.

Bank 1 is passenger side actually.

About O2 sensors: could the oil burn smoke from the external oil burning under the engine, which then accumulates under the hood, cause the O2 sensors to give bad readings? (external oxygen compared to oxygen in the exhaust)

[jrock]

That quart of oil missing might not be just from leaking oil but also from slight burning oil. You can perform a leak down test on bak 1 (driver side I believe) cylinders to diagnose the quality of your piston rings.

How do you perform a leak down test to check piston ring quality?

[onemoremile]

Could also be a bad PCV valve, worn valve guide(s), or worn ring(s).

[onemoremile]

How do you perform a leak down test to check piston ring quality?

http://www.carcraft.com/techarticles...ter/index.html

http://www.automedia.com/Engine_Leak...cr20080301lt/1

http://www.wcengineering.com/articles/leakdown.html

[B5A4Kevin]

valve cover gaskets and/or tensioner seals or cam plugs are most likely causing the external oil leak; and no, the o2 sensors would not pick up on the smoke from an external leak unless you had a huge exhaust leak, and if you have that, you have bigger fish to fry. i would check the pcv system, and do compression and leakdown tests as previously stated. another cause could be valve guides. afaik, the only way to check that would be to remove the intake and exhaust manifolds and take a look.

also, have you tried swapping your primary 02 sensors around? if you swap b1s1 and b2s1, and the fuel trims follow the sensor, it could indicate a faulty one. if not, then atleast you eliminated it without replacing it. the primary sensors should have black connectors.
good luck and hope to hear some results soon.