Jerry Garwick

Sorry if this is a beat-up question. I found a reference to the check engine light in the tech site but have a question regarding the oxygen sensor. I recently had my check engine light come on returning to California from a 3000 mile trip. I called a local Porsche shop and they told me to go home and have it checked upon my return, as it was a smog related problem. They said it may be the O2 sensor. I subsequently read in an magazine article that I should replace my O2 sensor every 50,000 miles. Is this so? Should I replace it out of principle prior to checking the codes or taking it in for a analysis? The car still runs great, by the way, but I am not pushing my luck until I get the check engine light straightened out.

Lorenfb

You should replace the O2 sensor even though the car seems to run OK
at 60K+ mileage. The sensor may cause the engine to run rich damaging
the cat.

You probably should have the DTC (diagnostic fault codes) read out using
the Porsche Hammer or using the blink code sequence. This should be part
of a regular service.

Good Luck
Loren

Adrian

Dear Jerry,
I agree with Loren that you can only have this confirmed by testing. There are DIY methods of checking the O2 sensor if you are a DIY person with knowledge about that the O2 sensor does and how it does it. The taking of the 964 to a Porsche shop is an option but there is another way that maybe cheaper. Here in Switzerland it is certainly cheaper. You have an emission test carried out. If the O2 sensor has failed you will fail the gas analyser check. It comes down to cost. I would do it the cheapest and easiest way.
As for replacing the O2 sensor on a regular basis this comes down to how often your 964 is checked. If you have like we do compulsory emissions tests I would only change it if I failed one of these tests. You have the check engine light and if the flashing codes is telling you that the O2 sensor has failed I would confirm and change it. If you do not have the check engine light, if you do not have compulsory regular emissions testing and you do not have the Bosch hammer used at service time then maybe a regular replacement interval is required.
Ciao,
Adrian
964C4

puma1824

Nothing like bringing back a 2 yr old thread.

Right now my car sits with a Check Engine Light (CEL) at the shop awaiting my answer on what I'd like to do.

Situation:
- Car originally in for clutch/brake bleed, replace brake lines with SS/Kevlar, and Shock/Strut replacement.
- Notified after job completed CEL on.
- Shop originally diagnosed with a loose plug/connector (not sure which one)
- CEL gone
- Went to shop to pick up and test drive. CEL initially off. ~3 miles down the road CEL on.
- Back to shop CEL on
- Diagnosed error code BAD KNOCK SENSOR

Shop Suggestion(s):
- Replace knock sensor(s)
- Replace O2 sensor (old)
- Replace MAF "looks old" <-- probably not nessary.

Car: 1991 964 C4 w/95K miles

Should I attempt to replace the knock sensor(s) and O2 sensor myself? Is this difficult? Anymore suggestions?

Marc Shaw

O2 sensor is easy to replace but can be very hard to remove the old one from the cat (the joys of rust) - are you handy with a propane torch?

Marc

Lorenfb

"Car originally in for clutch/brake bleed, replace brake lines with SS/Kevlar, and Shock/Strut replacement."

It's time to "back-track". If the problem wasn't there before the mechanical mods,
the problem was most likely "caused". Anytime a problem occurs, one needs to always
attempt to try and correlate with the problem what has recently changed.
Use this methodology versus the "shotgun troubleshooting" approach.

Check here ( www.systemsc.com/diagnostic.htm ) for more insights.

JasonAndreas

To replace the knock sensors you need to remove the entire intake manifold, even if you remove the cooling fan there isn't enough room to get a torque wrench onto the mounting screws (maybe with a tiny torque wrench but mine wouldn't fit). If the shop initially diagnosed the problem as a loose plug/connector and reseating it temporarily solved the problem I would try cleaning the pin contacts on the two green knock sensor connectors (first try the easy to get to connector on top of the engine). When your shop replaced the rear shocks they may have removed the left & right side of the intake manifold. So before you let your shop replace anything I would check all the connectors attached to sensors in the engine bay and maybe clean all the pin contacts.

puma1824

I'll definitely have them check this out first...wish me luck

puma1824

So I had inquired about the problem and they had indicated the knock sensor which was reporting the problem was the one that was harder to reach...anyways after a lengthy conversation about what I "need" and what I may want to do in the future, I decided to address the CEL/knock sensor problem AND do many things I was planning to do anyways within the next year. Here's the big $$$ list my car is being treated to right now:

- New knock sensors
- New MAF
- Engine drop to reseal engine -finally get rid of small leak(s)
- New clutch
- New engine soundproofing insulation thingy
- New wires
- New plugs

This BETTER get rid of the CEL and more!

-Puma

DarrylH

Ouch. It's gonna be fabulous afterward ! (BTW, I checked the dealer price on Saturday for an air flow meter: CDN$1700 so I'm gonna try cleaning mine again... .)

911nut

Puma,
I did the same...$3400....less the first two items. The clutch is great!
Jim