Failed Emissions Illinois 98 M3

[GG Allin]

My car failed Illinois emissions due to two bad o2 sensors and the cam position sensor. My check engine light does not work either, I suspect the guy I bought the car from. I'd like to do the work myself, I have a few questions.

My mechanic/freind says only buy the sensors from the dealer. They're twice the price. He's had bad experiences with the aftermarket ones. Does anyone here agree?

How do I identify which o2 sensors to replace? There's four of them, I need to replace "bank 1 - sensor 1" and "bank 2 - sensor 1"

Is the camshaft position sensor a DIY job?

[Xiphos]

You need to replace the pre-cat o2 sensors. Emissions only checks the pre-cat sensors, not the post-cat.

Rmeuropean.com is a great place to buy them from.

And yes, camshaft sensor is a diy job.

[Stef4o]

My car failed Illinois emissions due to two bad o2 sensors and the cam position sensor. My check engine light does not work either, I suspect the guy I bought the car from. I'd like to do the work myself, I have a few questions.

My mechanic/freind says only buy the sensors from the dealer. They're twice the price. He's had bad experiences with the aftermarket ones. Does anyone here agree?

How do I identify which o2 sensors to replace? There's four of them, I need to replace "bank 1 - sensor 1" and "bank 2 - sensor 1"

Is the camshaft position sensor a DIY job?

When changing O2 sensors , all 4 must be changed. Go with OEM. CPS is also DIY job. Got to have 32 mm open wrench to disconnect vanos solenoid and then swap CPS.

[vinnymac]

Replace both pre-cat o2 sensors. Check the group purchase forum. CMUZZY has a great deal running on O2 sensors. I bought 4 recently and did all of them on my 98 M3. It's a simple job.

The cam position sensor is really easy. You'll need a wrench to remove the vanos solenoid and the cam position sensor is right behind it. One bolt and a connector and it's out.

[Xiphos]

When changing O2 sensors , all 4 must be changed. Go with OEM. CPS is also DIY job. Got to have 32 mm open wrench to disconnect vanos solenoid and then swap CPS.

Uh...no. Pre-cat O2 sensors should always be changed out together as they are an integral part of the engine, and will throw a CEL and cause issues with emissions. Post-cat O2 sensors do not need to be replaced with pre-cats, they should be replaced when they fail.

There is no reason why you should buy all 4 new O2 sensors when 1 fails.

[Stef4o]

Uh...no. Pre-cat O2 sensors should always be changed out together as they are an integral part of the engine, and will throw a CEL and cause issues with emissions. Post-cat O2 sensors do not need to be replaced with pre-cats, they should be replaced when they fail.

There is no reason why you should buy all 4 new O2 sensors when 1 fails.

Well, 98 year cars must be close or past 100,000 miles. BMW states that O2 sensors must be changed at that time. Since he will be changing both pre-cats , why not order post-cats as well and do all the required maintenance?

[GG Allin]

Are the parts the same for pre and post cat sensors?

[Xiphos]

Are the parts the same for pre and post cat sensors?


Yes

[vinnymac]

Well, 98 year cars must be close or past 100,000 miles. BMW states that O2 sensors must be changed at that time. Since he will be changing both pre-cats , why not order post-cats as well and do all the required maintenance?



...because, changing out the post-cat o2 sensors before they fail is just a waste of money.

[thejlevie]

While you can't pass an emissions test with failed post-cat sensors, they are merely to indicate whether the catalytic converters are operating and have no affect on engine operation. The environment of post-cat sensors is fairly benign and they rarely fail. The pre-cat sensors are a critical part of the engine management system, being in the feedback loop for mixture control. They do have a finite life and should be replaced every 100k, or sooner if additive fuel trim climbs significantly.

[GG Allin]

One more question: When these sensors (cam position & o2) are replaced will the car run better?

[Xiphos]

One more question: When these sensors (cam position & o2) are replaced will the car run better?

new pre-cat o2 sensors will absolutely make your car run better if they were not working before.