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Re: Testing Oxygen Sensors

OK Gang, been lurking long enough...

Oxygen sensors are defineitely to be tested for accuracy, as the computer will
use this information to establish proper fuel mixture.

This testing is to be done (as others have mentioned) with a high impedence
digital instrument. A voltmeter will allow partial testing, but a lab scope
will allow full evaluation.

Now let's talk specs...all tests must be performed on a sensor at normal
operating temp.

1. Voltage must exceed 825Mv with engine artificailly enrichened (w/propane)
2. Voltage must read less than 175Mv with engine artificially enleaned (large
vacuum leak)
3. Voltage should never exceed 1 volt, nor drop below 0 volts EVER!
4. Switch time (here's where the lab scope comes in) must be less than 100Ms

These specs are there to verify that a sensor has the ability to report the
existing conditions accurately and in a timely fasion.

The computer system must have accurate inputs in order to maintain proper fuel

A biased oxygen sensor (one that does not swing to full values) will cause the
computer to chase mixture to undesireable levels. Since this is a primary
input for fuel control, proper test methods must be used to determine sensor

Just my .02 (Yeah I know, I'll figure it out sometime).

Mike Bywater

1988 80 Quattro (Lovin' every minute!)