87 325 trouble passing smog test

[DaveInLA]

My uncle's 325 eta has been failing his smog tests the last couple times. Each time, he would replace the catalytic converter, which would allow him to pass, and then 2 years later, he would fail again, prompting a new cat. In another 2 years, he'd fail smog once more.

He's had this car for about 10 years, 100K miles and has not changed the O2 sensor. As far as I know, he still gets decent mileage with his car, and whether or not he's running rich isn't obvious.

Obviously, changing the cat every couple of years isn't the right thing to do-- does this sound like an oxygen sensor problem? What else could cause the failed smog tests?

[MA325is88]

I went through this with a 318ic last year. This can be caused by a faulty thermostat, faulty emissions canister, vacuum leaks, and also incorrect spark plugs and o2 sensor issues.

Its hard to believe though that someone would go through all the hassle of changing the cat, and not put a new o2 sensor in when you would have to swap it anyway.

[DaveInLA]

Its hard to believe though that someone would go through all the hassle of changing the cat, and not put a new o2 sensor in when you would have to swap it anyway.

I'm not too familiar with exhaust systems-- are you saying that you have to remove the O2 sensor when changing the cat? If so, I guess the people who worked on my uncle's car kept the same sensor in place.

[DaveInLA]

I went through this with a 318ic last year. This can be caused by a faulty thermostat, faulty emissions canister, vacuum leaks, and also incorrect spark plugs and o2 sensor issues.

Also, how did you finally fix your problem? What ws the cause?

[MA325is88]

The two main issues were the thermostat and the incorrect spark plugs. The thermostat was stuck open and the engine was never getting hot enough, and the plugs werent a hot enough plug.

Mass is as bad as Cali, and it finally passed.