Bank 1 02 sensor reading higher (mVs)

[C7vette2014]

14 c7 fbos e85 btr cam ported heads

Just had a cam and ported heads installed, So im trying to chase down a stalling issue and thought it was tune related. A new tuner is looking over my logs and pointed out that my bank 1 02 is 10-12% higher (adding more fuel) then my bank 2 (1-3%). And watching a log you can see that bank 1 is constantly around 800 mVs and bank 2 is bouncing up and down really fast.

The tuner said the B102 is seeing lean condition and hence adding more fuel. What should i check to solve this issue besides a faulty 02.

[Haans249]

Great question. I have the same feature as well, one bank is reading leaner than the other at idle. Once I'm part throttle driving they read the same. It could be an exhaust leak near the O2 sensor.

[blindsquirrel]

Steady at 800mV is the opposite of lean.

[Haans249]

Oh good point, I missed that part of his post.

Tuner probably needs to add fueling at idle to get the trims down.

[blindsquirrel]

If it's at 800mV, and trims on that bank are positive, that's some other problem. Trims should be negative, trying to remove fuel, to bring the voltage down and get it switching again. Most likely it's a sensor problem.

[Haans249]

I have the exact same issue. I've replaced the sensor on the bank that is reading richer than the other (one is switching one reads in the 750's ish) when at idle. The new sensor didn't change anything. I also have my wideband installed to the same bank (2 for me) - which confirms the slightly rich condition at idle (.95 to .98 lambda). My STFT's are locked to each other between bank 1 and 2, they're always the same they don't deviate from one another. I'm not sure why, but the O2's are not controlling each bank independently. I believe this is the cause of the offset fueling, but never could figure out how to solve it.

It could have something to do with having my LTFT's turned off or possibly the rear O2's being disabled (since that is a known issue with the DFCO return to idle spike to +23% STFT for a second). Not sure and could never figure it out. Tune was close enough so I just let it be.

[C7vette2014]

Im gonna just tear the engine apart over the winter and inspect everything. I just had this btr 225 cam done and im dealing with this. Just gonna make sure none of my 02 wiring is nicked and make sure theres no exhaust leaks of intake leaks. I may have to do a leak down to make sure valves arnt leaking when closed. I heard that could cause issues like this as well.

[blindsquirrel]

Are you sure the trims on B1 weren't negative, and not positive? It really shouldn't be able to add fuel with the O2 voltage that high. It should be subtracting.

If trims were negative on that bank with high O2 mV I'd say... drippy injector, maybe?

[C7vette2014]

This is what my tuner sent me through email:

"Has anyone told you to check for exhaust leaks? Your bank 1 (driver side) is adding up to 12% fuel while your bank 2 (passenger side) is only adding 1%-2%. That's a pretty common sign of either an exhaust leak or vac leak. Could also be a plug issue I'd pull all the plugs and check them out and see if how they all look.

On the cold start, it's showing your bank 2 is right but bank 1 isn't doing anything.

I'd start with checking plugs, plug wires, and making sure everything is tight on the intake and exhaust side. Also, check your o2 sensors to see if a wire is burnt. "

[blindsquirrel]

O2 reading rich and trims responding by adding fuel just does not compute. Something getting mixed up here.

[Haans249]

Do you have LTFTs enabled?

[C7vette2014]

When i watch my log i can see that bank 1 is reading alot higher the bank 2 (mVs). Like bank1 is around 750-800 mVs jumping around. While bank 2 is jumping up and down up and down rapidly. I can post a log.

[C7vette2014]

Im assuming if you mean can i read my LTFts, yes, in my logs

[Haans249]

Im assuming if you mean can i read my LTFts, yes, in my logs

Make sure to include the LTFTs in your log as well as the STFTs. Do you have a wideband installed? Include that too.

Does this happen only at idle or also while driving?

[C7vette2014]

Idle starts are rough, cold starts it stalled. low speed driving(parking lot driving or bumper to bumper traffic). That seems to be the problem areas. Cruising seems fine, according to my logs. Ill attach some.

[blindsquirrel]

Both logs clearly show both O2s are switching.

[C7vette2014]

Yeah they are, but bank 1 is alot richer no?

[blindsquirrel]

Fuel trims are a response to the O2 sensors, trims do not just do their own thing to see what happens to the O2s. Positive trims means it thinks it is lean.

The two sensors do look different. Normally when one sensor is switching slower than the other it's a sensor issue. Old, fouled, something. O2 sensors get worn out long before they go completely dead and set codes.

[C7vette2014]

Yeah i think you summed it up, my new tuner is seeing that difference and befor we go deep dive into a new tune he wants me to make sure the car is sound. The car drives fine, its just it likes to stall and stumble at low rpms when coming to a stop, or brake torquing. Cold starts are rough to. It stalls when i start it and haves a rough time staying idle and i have to manual gove it gas but then it levels out after about 30 secs and stays running.

[C7vette2014]

So i tore my headers off and all 8 exhaust ports were black and dry except drivers side number 5. Looks like oil and wet. Not sure if this would cause my original problem, looks like valve stem or a seal.