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O2 Sensor Voltages - Ahead of Cat

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Just got myself a durametric and been doing a bit of playing with the actual values. Have been looking at the O2 sensor values and am a bit puzzled.

From what I understand there are 4 o2 sensors, and this seems to match the options on the Durametric. I have recorded values for "Oxygen Sensors Cylinders 1-3", "Oxygen Sensors Cylinders 4-6", "O2 sensor voltage ahead of cat. c." and "O2 sensor voltage ahead of cat. c. bank 2".

The first two started recording values slightly either side of 1.0 (0.9 to 1.14) and averaged 1.0. The values for the two ahead of the cat converter both averaged around 0.4 and varied between 0 and 0.9. I had expected these to also be averaging about 1.0 and not moving too far from 1.0.

Have I misunderstood whats going on here?

Note that when I first plugged in the durametric I had code P0134 (Porsche fault code 10 - O2 sensor ahead of cat conv bank 1), but I have cleared this and so far it hasn't come back.

Grateful for any advice.



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I have no knowledge specific to the Durametric software, but the reading on the before sensors is well within range. The after cat sensors should also be within the same range. The precat sensors measure the air:fuel mixture as it comes from the engine and reports the level by way of a voltage. The range is between 0 - 0.90 volts. (+/-). The target for the precat sensor is 0.45 volts which is the targetted air:fuel ratio of 14.7:1). Voltage below 0.45 signals the computer that the engine is running lean and the computer will compensate by adding fuel. Voltage above 0.45 and the computer will reduce fuel.

The aftercat sensors read the air:fuel mixture after it has passed through the CATS. The computer does nothing with the reading except report an error if the reading is out of a predetermined range. The voltage range is also the same as the precat sensors, 0 - 0.90 volts with 0.45 volts reporting 14.7:1.

In your case, check the settings on the Durametric. I don't know if they are adjustable, but it appears you are not reporting voltage on the aftercat sensors. Many scanners can also show LAMBDA numbers in which "1" represents a 14.7"1 air:fuel ratio. Lower = richer and higher = leaner. This style of reporting can easily be used to determine your air:fuel ratio by taking the reported number and multiplying it by 14.7. i.e. a reading of 1.02 would mean that your engine is running lean with a air:fuel mixture of 15:1 (14.7 x 1.02) IMO, reading the voltages is much easier.

Edited by 1999Porsche911
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