In a message dated 98-08-05 03:36:49 EDT, kayfremgen@JUNO.COM writes:

<< Went through the Digifant/Bosch system and came up with a O2 sensor
 question.  With O2 sensor unhooked from the computer the engine will
 accelerate fine under load (AC compressor on).With the sensor hooked up
 the engine has severe hesitation.  One would think: exchange the O2
 sensor and get on with your life, but here's the kicker.  With the volt
 meter hooked up to the now back inline O2 sensor I'm getting readings
 which to my knowledge are correct.  In idle the volt meter bounces back
 and forth between 0 and 0.6 volt.  During acceleration under load (A/C
 compressor on) the volt meter then drops to "negative" 0.1 volts for
 about 3 to 4 seconds which is approximately the same duration of the
 hesitation. Indicating a lean mixture.

 Question #1: Isn't this exactly what the O2 sensor is supposed to do?
 Question #2: Why is the computer not compensating for this voltage drop?
 Question #3: Why am I getting "negative" 0.1 volts for about 3 to 4
 seconds? (using analog gauge need to switch polarity to measure negative
 volts)
 Question #4: Will a new O2 sensor fix this problem?

 Additional data if needed, compression check #1: 150, #2: 175,#3: 135,
 #4: 165.  Vacuum test (intake manifold) at idle 14.5 in. at 1500 rpm 17.5
 in., at 2000 and up 20in. Hg (Live in Florida elevation 0) 135000 Miles

 Any help is highly appreciated, Thank You

 Kai  87.2 Westy >>
Kai, what matters is, what is the voltage reading from the O2 sensor  with the
O2 sensor wire disconnected. For the best results fuel mixture wise, you need
to adjust the fuel mixture so that you see an average of about .7 volts (700
millivolts) , wich would be about .8 to 1.0 CO at sea level. I know that .5
volts is perfect air and fuel mixture, but you need to adjust it this way for
best results, especially for the first few minutes of the cold start run while
it is still in open loop ( open loop = when O2 sensor voltage isn't being used
until engine is warm enough per the signal from the temp sensor ). Note that,
it is very important that your temp sensor for the fuel injection is new also.
A new O2 sensor isn't going to fix a bad temp sensor.  Good luck, and let me
know how it goes.
 Michael Modl
 87 syncro
\ 87 Quattro.