[tomj76]

I have a '96 with the 3.8L V6 Engine. I have 315k on the engine.

When running at idle, the scan tool shows a "normal" trim, slightly lean (+5%). However, at 2000 rpm it changes to a negative trim (-15%) to compensate for a very rich condition. I've been getting bank 2 rich codes. It also blows black soot from the tail pipe at 2000 rpm.

I know that I'm burning oil, at about 1 qt every 200 miles. There is oil found in the pleats of the plenum between the throttle body and the PCV pipe. This could account for the rich reading, if the oil is "counting" as fuel by using a portion of the O2 entering the combustion chamber. I've also found severe oil deposits on the plugs in cylinders 4, 5 & 6 to the point of causing misfire.

I use it mostly for short trips, which probably is a factor in the amount of oil used. I've switch to 10W40 to improve the oil consumption somewhat.

Although I'm planning a complete overhaul of the engine (why wouldn't I at 315k miles?), I'd like to identify the "big pole in the tent". I tested compression and saw good wet/dry compressions (in spec) of ~190 psi dry, ~210 psi wet. Cylinder 2 was a bit low the first time I tested is (150 psi dry), but I reteseted it the next day and it was better, even better than the wet test than the previous day.

I also measured leak down, and found that all cylinders were better than 20%, with most of the leakage detected on the oil dipstick tube.

While I suspect that the problem is likely valve guides & seals, I'm wondering if anyone can explain why it runs rich at high RPM. Is this evidence of a bad oil ring, or something of that nature?