I've attached a file of data I logged on my 1998 M3. I've been getting a CEL after replacing the head for the second time. The thrown codes are:

P0170 - Fuel Trim Bank 1
P1188 - Fuel Control Bank1 Sensor1

Looking at the data, the B1S1 voltage hovers around 0.98, and the B2S2 voltage jumps around a lot more, centered around 0.45v as expected. Here's a link to the zipped data file:

http://standingwave.org/dump4.zip


http://standingwave.org/o2_data.gif

I checked, and the O2 sensors are connected to the right connectors on the fuel rail.

Bad B1S1 O2 sensor? Vacuum leak in the B1 side of the intake manifold?

Thanks.

-HoB

What did you use to log this data? Are you logging over the OBD port, or directly logging the voltage of the sensor? If you are logging over the OBD, it would be interesting to now the injection quantity for both banks.

To test the O2 sensor, you could just switch the sensors from either bank because B2S1 is working well. What does the post catalyst sensor (B1S2) indicate? Does it confirm this lean condition? If the post catalyst sensor indicates rich, then the B1S1 sensor is bad.

A vacuum leak would probably cause misfire as well which would cause a misfire code. The engine will probably also run rough if this is the case. At wide open throttle, you should be able to make the sensor go to a rich state, because the effect of a small leak will be very small at WOT. If you have a vacuum leak it is probably at the intake manifold gasket or it would affect bank 2 as well.

The data was logged with my AutoEnginuity OBD-II scan tool. I will try to sample the injector flow data. I will also look at the post-cat data.

Yeah, first test is to swap the O2 sensors. Whee. Love trying to get those things out of the headers. :eyecrazy

-HoB

That sounds like no fun

It looks to me that your pre-cat bank 1 O2 sensor is bad.

So I swapped the B1S1 O2 sensor with a different one. So far the problem has not returned. Looks like it was a toasted sensor.