Steady .03v O2 sensor reading

[gijoe985]

I have a steady reading of .03v from my o2 sensor. Just got the car and put in a new motor. It does not go up or down at all. I get high knock counts when I rev the engine up high. The irony is that I have the same problem in my 3kgt vr4 as well. Two different vr4s, both with steady .03v readings. With the 3kgt I found out it was dirty injectors. Maybe it is the same here. I was just looking for some ideas of what else it could be.

I guess I will add, in hopes that it sparks some conversation, that it is to my understanding that a flatlined o2 DOES NO mean that the o2 is bad, for certain. It could be that I am just running very lean. But maybe not. I am getting knock if I rev the engine above 4k. Maybe I should pull my injectors and test how well they are firing.

 

[jukematt]

So after you cleaned the injectors on your 3kGT VR4, the O2 reading was fine? If so, then I guess that could be the same problem on your GVR4. I haven't heard that before though.

The O2 should be constantly oscillating between 0 and .9V. Do you have a wideband hooked up? I do and I noticed I was running super rich then got a CEL after driving a bit longer. I ran a log and the O2 was fine for a while, but then it started getting constant readings and that's when I would run rich. It wouldn't correct itself either unless I shut off the car for a while. Then the same problem would return after some driving (especially if I boosted at all). So I'm going to replace my O2.

Good luck!

 

[gijoe985]

From what I know about o2 sensors, and I am open to correction, the oscillating voltage is not created by the o2 sensor itself. That is created from the engine running in closed loop and continually adjusting the fuel. The o2 sensor just sends out a signal of what it is reading.

Therefore, if am just starting my car, and in open loop, and I am running lean, then a constant voltage from my o2 could be a correct reading. Just very lean for me .03v.

 

[jukematt]

Sorry I had forgotten about this thread. I wasn't entirely positive how the system worked but I had an idea and this seems to confirm it:

WHAT THE HOME MECHANIC NEEDS TO KNOW ABOUT O2 SENSORS

When the system is running properly, the car is started, and the ECU runs in open loop: so a fixed amount of fuel is injected. Once the O2 sensor heats up (or in some cars like my 2G where it has heated O2 sensors), the ECU takes cues from the sensor's reading, called closed loop. But the ECU is "dumb". It takes a reading that the O2 sensor says everything is rich so it reduces fuel, then it sees the sensor says everything is lean, so it adds fuel again, starting the cycle over again. This is what causes the "oscillations". The ECU is constantly compensating itself to keep A/F ratios normal.

When the O2 sensor is reading a constant or near constant low voltage then there is a problem. From my experience, it is most likely a bad O2 sensor. However, a bad vacuum/boost leak or a bad coolant temperature sensor can also prevent the system from entering closed loop.

What logger are you using to measure your O2 sensor voltage? I would run a boost leak test, watch your coolant gauge, and check your coolant temperature with the logger as well. Clean your injectors while you're at it since that was causing your previous problem. If everything checks out, I would try a new O2 sensor.

 

[gijoe985]

Well, I pulled my ECU and had bad ISC drivers. Caps looked ok, but I'm sending it in to EMCtuning to get it all checked out.

I agree with all the stuff you said above about how O2 sensors function, which is partly why I wanted to check other things first. Just because it doesn't cycle voltage, doesn't mean it is bad, it could simply be that are are in fact running lean.

Just got word back on my 3kgt that 3 of the 6 injectors were irreparable. Ah well...

 

[Nitrobasher]

I have a similar problem with my GVR4. .04v from the o2 sensor throughout a pull. With high knock when the engine feels a load.

Please keep this updated.