'99 996 - Is o2 sensor ahead of cat pre or post?

[Lamplighterson]

http://thumbsnap.com/euecD44s

Need to replace the o2 sensor with an oem part.

o2 oxygen sensor "ahead" of catalytic converter.

Is this considered post or pre cat?

http://www.ebay.co.uk/itm/350713832985?ssPageName=... : post

http://www.ebay.co.uk/itm/230927927761?ssPageName=... : pre

So which one is considered "ahead?"

My 996 is an early one so only has 2 o2 sensors in total rather than 4 on the later models...

[Rockster]

Pre is considered the one ahead of the converter. Early Porsches (and some sold in various regions) only came with the pre-converter sensors. These sensors are used to monitor the oxygen content of the combustion gases to know the DME has control of the fueling.

The post converter sensors are used to monitor the performance of the converters, when of course the post converter sensors are present.

Handle the new sensors with extreme care. Do not touch the tips. Do not use any thread lubricant. Make no attempt to measure electrical resistance between the tip and anything else.

Be careful with the wiring harness electrical connectors. They are getting on in age and are fragile. Route the sensor wiring just like it came from the factory.

Be sure the connector seats completely into the wiring harness connector.

[Lamplighterson]

Fantastic. Many thanks for the comprehensive reply.

All the best.

[996TT02]

Rockster said:

Do not use any thread lubricant. Make no attempt to measure electrical resistance between the tip and anything else.

Normally recommended to use anti-seize on the threads, don't get this. Just bought a new Denso for my MX5 and it even comes with it, in a little "pillow" pack. Certainly, with instructions to keep it OFF the sensor itself i.e. only use on the threads.

[Sump]

i used Bosch universal ones and it worked great!

Just need to solder the old connection onto new one. Very easy just match the wire colours!

[Rockster]

996TT02 said:

Normally recommended to use anti-seize on the threads, don't get this. Just bought a new Denso for my MX5 and it even comes with it, in a little "pillow" pack. Certainly, with instructions to keep it OFF the sensor itself i.e. only use on the threads.

Anti-seize is seldom recommended by the factory for use anywhere.

Even though one might be careful and not get any anti-seize on the sensor tip, as the sensor heats up this forces the stuff out through the threads towards the tip where the stuff ruins the sensor.

There is supposedly O2 sensor safe thread lubes (primarily no silicon) but the sensors -- at least the ones from the dealer parts counter -- already come with thread lube safe to use with sensors.

[Rockster]

Sump said:

i used Bosch universal ones and it worked great!

Just need to solder the old connection onto new one. Very easy just match the wire colours!

Do not solder the O2 sensor leads. The solder biases the voltage reading and this can affect fueling. If the leads must be connected one should use proper crimp connectors. Better still is to simply buy sensors that have the proper length leads with the vehicle wiring harness connector already attached.

[Sump]

Well I don't even know why I said solder as I didn't even solder mine.

According to durametric it's all good.

[Rockster]

Sump said:

Well I don't even know why I said solder as I didn't even solder mine.

According to durametric it's all good.

Durametric is not able to detect bias. The DME would just use the biased readings and end up fueling the engine sub par.

[996TT02]

http://www.renntech.org/forums/topic/19211-solderi...