Tough one: engine runs rich - O2 says lean

[Bruno]

535i M30 engine: Engine runs rich (worse at idle). The disconnected O2 reads 0.02V saying super lean. Engine light is on: "O2 problem or to lean or too rich condition"

- Changed O2: same reading. Changed it again, same readings
- Changed injectors
- Changed distributor rotors and cap
- Checked continuity on the O2 wires to the DME and any grounding
- Checked all the vacuum hoses
- Checked coolant sensor
- Changed the Air Flow meter
- Cleaned ICV
- Changed Air filter, spark plugs, did oil change.
- Changed catalytic converters.

Car runs great other than that.

- Will adjust the valves and spaks plug gap, and try to fix the little exhaust leak near the O2 sensor.

Soooo, what did I miss? Why would the O2 read a lean condition all the time? And sending wrong info to the DME. Pulled a spark plug it was black because DME sends more fuel...

[ironie]

My bet would have been a leaky injector. were the plugs you pulled all black?
I would look at the CPS too. You are right, That is a tough one.
Good luck

[winfred]

temp sensor reading? out of spec temp sensor will screw with it cold and hot readings crossed checked off the chart in bentley, the 02 sensor may not be getting hot enough to read hence the low voltage (535s usually run the 02 sensor heater off the fuel pump relay instead of it's own relay so if it's running the heater is probably working) may be too fat for the sensor to light off, fuel pressure? high or low will screw with it

[Bruno]

temp sensor reading? out of spec temp sensor will screw with it cold and hot readings crossed checked off the chart in bentley, the 02 sensor may not be getting hot enough to read hence the low voltage (535s usually run the 02 sensor heater off the fuel pump relay instead of it's own relay so if it's running the heater is probably working) may be too fat for the sensor to light off, fuel pressure? high or low will screw with it

Checked the voltage for the heater, I do get 12V, so the O2 heater works.
I let the car warm up before taking the measurement off the O2.

I will change the fuel filter and Pressure regulator next. But if the O2 is reading lean and the Engine is running rich... I wouldn't think that the fuel regulator is the problem no?

Thanks.

[Anton CH.]

I am thinking you might have a gasket that is leaking oxygen into exhaust somewhere.

[Ferret]

Is the exhaust leak before or after the o2 sensor?

If it's before, it's dragging fresh air in and screwing with the reading - just making it overfuel even worse.

[Anton CH.]

Is the exhaust leak before or after the o2 sensor?

If it's before, it's dragging fresh air in and screwing with the reading - just making it overfuel even worse.

Exhaust leak doesn't necessarily have to be upstream of oxygen sensor. Just in near proximity.

[Ferret]

Exhaust leak doesn't necessarily have to be upstream of oxygen sensor. Just in near proximity.

If it's downstream of it, it'd have to be very close to the sensor, as I dont think fresh air could easily backflow up an exhaust, even at idle?

[Bruno]

Exhaust leak doesn't necessarily have to be upstream of oxygen sensor. Just in near proximity.

Ok, there is a leak near the O2 for sure, I can feel it... that should be a starting point. I will try to locate it then JB weld or go back to the muffler shop and have them work their magic.

Thanks that is a start.