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re- oxygen sensor

> Fred Hu writes
> What will go wrong if it is not replaced?

Primer:  The oxygen sensor measures the amount of oxygen in the exhaust
    gases.  The Motronic unit uses this (and several other things) to
    adjust the duration of time the fuel injectors are open.  This causes
    the fuel/air mixture to increase (richer) or decrease (leaner). 
Oxygen Sensor:  The sensor uses a platinum coated electrode to obtain these
    measurements (which explains their expense).  The electrode is
    extremely sensitive to everything, so it is very easy to ruin a new
    sensor by getting sloppy with the antiseeze.  The signal produced by 
    the sensor is super low, so periodic cleaning of the contacts and
    terminals is a must.

The way to check the O2 sensor for proper operation is to connect an ohmmeter
across the sensor and compare your results with the specs given by the factory
(Just bug a BMW dealer for the specs and which terminals to connect to).

When the O2 sensor fails, the Motronic unit interprets the signal as a mixture
which is too lean (not all of the air is being burned).  It tries to adjust by
increasing the amount of fuel to the cylinders.  This could result in several
things.

    - Uneven idle when warm (The O2 sensor signal is ignored when cold)
    - Firing back through the intake plenum (Especially during coastdown)
    - Overall decrease in performance/efficiency

The motronic engine map for timing and fuel/air ratio vs engine load and
engine rpm is very elaborate and depends on everything working properly.

To whom it may concern, I am intimately familiar with the Getrag 5 speed in
the E30's.  You don't need to buy expensive BMW tools to rebuild the tranny
when you can easily fabricate them.

R/
85 318i
95 M3 shaped space in the garage