Hello all,

I originally posted this on the 991 forum by mistake - woops.....

This is one of my first posts to this board although I've been lurking for a while.....

I plan on carrying out a 60k mile service on my '90 C2 next month. This will be my first 911 service and I've been reading everything I can on valve adjustment and all of the other items that I need to do.

I have one question that I still need to answer - should I replace the O2 sensor as a matter of course or should I wait until the unit fails? I understand that these units fail progressively which makes me think that I should just replace it at the 60k mark.

Will a failing O2 sensor show up as a fault - will it cause the warning light to come on? If so, can I wait until it does before changing it?


TIA,


Doug

 

Actually, you also posted it on the 911 forum, where one person responded.

 

Bill,


Yes - I posted it on the 911 forum originally but couldn't figure out how to remove it or move it to this forum - these options need admin privileges..... Do you know how?

Yes, the service interval is 30k - that's why I'm looking at replacing it but since it's a relatively expensive component and the downside of failure is mild I was wondering if I could wait until it fails and replace it then.

Any ideas?

 

[quote]<strong>I posted it on the 911 forum originally but couldn't figure out how to remove it or move it to this forum - these options need admin privileges..... Do you know how?</strong><hr></blockquote>

Ask and ye shall receive: Poof! Gone!

I believe the recommended service interval on the O2 sensors is every 30K, which would target it for replacement at the 60K service. Since DME relies on the O2 sensor as a major input (and since I don't like driving in limp-home mode) my two cents would be to replace it. You can buy generic Bosch multi-wire O2 sensors at a savings over the Porsche boxed variety. I believe the only difference is that the Porsche boxed variety comes with a cover over the top of the O2 sensor, which can keep water out of it.

 

Dear Scotsman60,
Your 1990 model 964 will switch into limp home mode once. If you shut the engine off and restart you will stay in open loop mode and will run rich. You will fail an emissions test with a failed O2 sensor.
I personally believe with such things to let them fail then replace them. However that is only my way and if you feel prevention is better than cure in this circumstance it is up to you. I am afraid I have to disagree with Bill on the O2 sensor purchase. I recommend the extra dollars are worth it for the Porsche version. If you never drive in the wet or wash your 964 the cheap ones are okay but they really do not like water and their location on the 964 is not good unless sealed properly. Please do not use sealant on them either. There is a inconvenience risk and lower reliability risk with these cheap versions,
Ciao,
Adrian
911C4

 

Bill, Adrian,

Thanx for the input. I think that I will replace the unit with a Porsche one during the 60k service. I checked the 30k service record and could find no record of it being replaced at that time. I'm aslo concerned that the unit can fail progressively - reacting slower and slower to the exhaust gas content and with the voltage/resisitance values gradually wandering out of spec.

I don't have the tools to test the unit so I'll pay the money and replace it next month.


Thanx!!!!


Doug

 

What I do as a test: Pull a few spark plugs and check the colour. If its fine, its fine, why bother. I would never replace such an expensive part if I know it is still good. You should rather spend the money on spark plug wires, caps and rotors (expensive too).

 

[quote]<strong> I am afraid I have to disagree with Bill on the O2 sensor purchase. I recommend the extra dollars are worth it for the Porsche version. </strong><hr></blockquote>

Actually, I agree! When I replace mine in another 10K miles, I'll use the Porsche version. I was just suggesting that there is an option, and with all options you need to consider the pro's (less expensive) and cons (engine performance may suffer in the rain/others).