o2 sensor questions

[ericem]

Hey how greatly can the o2 sensor affect performance? When is the o2 sensor's input mainly being used? How does exhaust temperature affect it's readings?

[JT95]

From what I hear, driving around with a goobered O2 sensor will hurt your MPG and leave your idle rough. I know a guy who has been driving for a year now with a bad O2 code.

[ScottG]

My understanding is that the 02 sensor is a main provider (along with the accelerator position sensor) of signals that control fuel flow (how rich or lean the fuel rato is) When the main 02 sensor (the front one) fails, the system tends to default into a 'rich' mode, causing excessive fuel consumption, (as though you were running a carbureted car with the choke pulled out).

 

Common Subie wisdom says to replace the front 02 sensor with a dealer supplied unit. Aftermarket replacements have a history of early failure.

[Fairtax4me]

The O2 sensors sole responsibility is monitoring burned exhaust gases and reporting the oxygen content of those gases to the ECU so that it can adjust the A/F mixture accordingly. There are a lot of factors that go into how much fuel is consumed, air density, air temperature, throttle position, engine RPM, engine temp., and so on. The O2 sensor is more for fine tuning the mixture to give optimal fuel economy for the conditions, and helps to maintain proper combustion temperature which helps keep down harmful emissions creation.

 

The O2 sensor doesn't work until it reaches about 600°F. This is why the upstream sensor is usually located very close to the engine, usually right at the point where the exhaust pipes from each bank of the engine (or each cylinder on a inline) come together. Most V engine cars use a sensor for each bank. Modern sensors have heaters built in to help get them up to operating temperature faster. Other than that temperature has no effect on the sensor. It does not measure exhaust temperature in any way. However, it can be used to calculate exhaust temperature range, based on the output signal created by the sensor. Given that the sensor in in proper working order, and the fuel mixture is "normal" If the sensor sees more oxygen, the mixture is lean, which indicates a higher temperature. If you've ever blown on a fire, it gets hotter. Same principle applies to internal combustion. More air = more heat. If it sees less oxygen the mixture is rich, which makes a cooler burn, thereby lowering exhaust temperature.

 

The ECU starts using data from the O2 sensor as soon as it is available(after the sensor warms up). Generally within a minute or two of starting the engine. It will begin adjusting fuel mixture as soon as it gets a reading from the sensor. But the optimal (most efficient) AF ratio will not be achieved until the engine coolant has reached operating temperature.

[ericem]

Hmm, how important do you think the TPS is? I am thinking about adjusting it tomorrow. Could it possibly be affecting fuel economy?

 

I just don't like how my exhaust is so thick with carbon, and when I hit boost doesn't really go much faster. On cold days it's great though!