CEL O2 Sensor

[Dussen]

So as the title states we have a CEL on due to O2 sensor. Now before I go into to much detail I'm going to start with the basics. We have tried a lot of different things and cannot get the light to clear. However every once in a while it wont even come on. The light has been in for about a month now and like I just stated, it's sporadic.

This is what we've tried:

replaced the O2 Sensor and no fix
checked fuses everything is good
checked relays all good
checked for a vacuum leak using a propane torch and nothing found

With the car cold the resistance on the O2 Sensor is less than 5 ohms as it should be but once the car warms up the resistance goes up over 5 ohms which would cause the CEL to energize. We have power to the O2 heater and it seems to be working correctly.

My question for you all is, What our we missing here? There must be something we have overlooked or just haven't tried. We are thinking about cutting the CAT open to see if that's clogged but we have not a clue where to go next. We kind of wanted easier measures first.

Thanks,
Dustin
and
Aaron

Oh before I forget this is for a 87 325iS.

[b*saint]

The o2 sensor could be working fine, just generating a signal due to something else making it give a reading which would result in a CEL.

i.e. a capacitive height sensor would give you a sensor fault if you were calibrating off a non grounded block. Its not the sensor's fault.

[jlevie]

My guess is that there are intake leaks. A smoke test is the only real way to find them. You should also check rail fuel pressure.

[Dussen]

The o2 sensor could be working fine, just generating a signal due to something else making it give a reading which would result in a CEL.

i.e. a capacitive height sensor would give you a sensor fault if you were calibrating off a non grounded block. Its not the sensor's fault.

Block is grounded so I'm not sure that is it.

[Dussen]

My guess is that there are intake leaks. A smoke test is the only real way to find them. You should also check rail fuel pressure.

Due to our lack of equipment we haven't tried a smoke test nor have we check fuel rail pressure.