odd oxygen sensor reading.... STFTB1 positive, STFTB2 negative

[jakeb]

This is a swapped LQ4 into a 81 BMW 5 series. It has only been running maybe a max of 10-20 minutes. I did all the wiring on the swap....second swap I have done like this. I was hooking up my wideband so I can adjust the tune and noticed something a little odd.

The STFTs are opposite of each other. One shows positive and one shows negative. The narrow band oxygen sensors are reading much different from each other as well. And if you look at the wideband it is showing leaner and leaner and then it drops back down again.

Wideband is in the passenger side bank.

I thought maybe I had the oxygen sensors flipped...pass on drivers side and drivers on pass but I checked the wiring back to the PCM and it is correct.

The drivers side narrow band O2 sensor is closer to the head than the passenger side if it makes a difference.

If someone could look at my short log that would be great. I assumed both banks should look similar. Any ideas why it is doing that?

The log is really short...shows a cold start up and then flipping to closed loop. AFR shows very lean on the wideband.....
I do have a couple exhaust leaks I am working on sealing up but they are all after the oxygen sensors....

thanks

[mecanicman]

You sure they are not swaped? unplug the the one on the driver side and scan and post up.

[Ben Charles]

Bank 1 is pumping in more fuel, look for a problem on that side

[jakeb]

Yes I am sure they are not flipped...even though it really looks like they are flipped from that log. I will disconnect the drivers side and post of a log.

What should I be looking for on bank1?

If I understand it right before it goes to closed loop it actually is showing rich on bank1. Then my wideband is showing very lean.

Also doesn't seem odd that the command AFR drops down to 13.13 and at that same point the STFT go to 0 and the narrowband sensors, mostly bank 1 goes rich again....

[WS6FirebirdTA00]

STFTs will be zero any time it is in open loop.

As soon as the car enters closed loop, at least it looks like it is entering CL, is when you have trouble. If bank 2 should not be pulling fuel if it is lean, how old are the o2 sensors? I woudl let it run longer to see how it does but the sensors could be crappy. Bank 1 makes sense, the sensor drops out and needs a lot of fuel added. I would run it in open loop and get the fueling tables tuned first, they are not even close from what I see. In OL you are commanding 13:1 and getting 15:1.

Post pics of where the o2s are located, where are they in relation to the collector.

How far past the o2 sensors are the leaks? Leaks after the o2s can still mess with the readings, depending how close they are.

[jakeb]

Thanks for the info...the sensors are actually brand new.

Because this swap is so tight the drivers side manifold actually goes forward and then comes around the front of the engine and exits on the passenger side. The exhaust leak on the drivers side bank1 is pretty far past the sensor. I would say at least 18"

Here is a picture of the manifold.


And where the oxygen sensor is. There are no leaks before the sensor at that flange.



The passenger side is a fbody manifold. Sensor is down below the car...here. There is a leak on this bank pretty soon after the sensor. The sensor you see there is an old one and where the pipe is open there is a clamp for the rest of the system and there is a leak there...so maybe 6" or so past the sensor. Wide band is in the bung that is open in this picture.



Here is a picture of the entire manifold...sensor is 6" from the open end.


The engine is a LQ4, LS6 intake, TR224R cam, running 411 PCM from a 02 fbody. It is running a truck maf and I pulled the table from an 04 2500 truck. VE tables from a LS6 vette (IIRC). So maybe what is happening is bank1 is reading poorly because of the leak just past it. Bank1 is actually reading correctly and everything needs more fuel.
Plan is to fix the exhaust leaks today. I will put it in open loop and see what I am getting. Should I do VE first and then MAF? Or because I am so lean right now would it be ok to richen the entire VE a little bit and the MAF some too? Higher maf numbers will get me a richer mixture correct?

Another quick question. I have my wideband system ground grounded through the HPTuners box on bin 5 (gnd). Is that what I should be doing? The readout on my wideband matches the readout in HPTuners.

thanks again for all the help!!

[WS6FirebirdTA00]

VE first then MAF, yes higher is more fuel.

You should be good as long as the readings match.

[jakeb]

great, thanks for the help

From what you see in the pics and me explaining does it sound like it could be a exhaust leak messing with the narrow band on bank2? Seems like that narrow band is always about the same reading, ~550mv

[WS6FirebirdTA00]

Normally a leak would make it read quite lean. Try to unplug it or put it in fresh air and see if it goes closers to zero.

[jakeb]

Here is another short log I forgot I had. This is logging before it started as well. Showing bank2 o2 as near stoich already and bank1 o2 way lean (like it should before starting correct?)

Maybe that bank2 o2 sensor is bad. Or the wiring to it is messed up.

They are both brand new sensors but I am sure there are even new sensors that go bad sometimes.

[WS6FirebirdTA00]

Yeah, normally when I see something around 450 mV and steady it tends to be dead or have no signal.

Unplug it and see if it drops to 0 mV.

[jakeb]

thanks, I'll check when I get home from work. Drives me nuts when I can't test something right away.

So if it goes to 0v then I know the wiring is good and the sensor is more then likely bad.

Thanks again for the help. I really appreciate it.

[planethax]

.....So if it goes to 0v then I know the wiring is good and the sensor is more then likely bad......

No it should still read 450mv unplugged

[jakeb]

Ok, picked up a new sensor on the way home today as I had to stop to get other stuff. Disconnected the sensor I had it in there and was getting 450mv with the connector disconnected. Checked the wires back to the PCM and everything ohmed out.

Then I noticed on the old bank2 sensor connector on the harness one of the pins was pushed back into the connector. It was ground or power for the heater. Pushed it back where it should be and then I plugged the sensor back in....wire pushed back out. Pull the sensor out and find that one of the female pins is buggered up.

Here is a picture


So the sensor must have been working but the heater was not, hence the odd readings.

Hooked up the new sensor I got and had it just hanging there....wasn't getting a reading other than 450mv. Threaded it into the bung and started getting a good reading matching the drivers side as they both heated up.

I didn't think the sensor grounded through the bung. I thought all the grounds were though the wiring. must not...

Attached a log with the new sensor. not running as I want to fix exhaust leaks tonight and then everything will be hot.

Look better now?

I expect this will fix the odd STFT issue. Once I get it running again I will report back.

[jakeb]

Also I checked the DCTs and it came back with a o2 B2S1 heater error(old,saved). Guess I need to get that MIL hooked up.

[WS6FirebirdTA00]

No it should still read 450mv unplugged

Totally slipped my mind, my mistake.

[jakeb]

Ok, new oxygen sensor in and things are looking a lot better. Tune is way off but at least now both oxygen sensors look similar.

I am having trouble with it stalling when coming to a stop...clutch in and idle drops and does not recover. I assume this is because of the idle airflow or just general VE/MAF that needs to be calibrated/tuned.

Should I add some air to the idle air flow to keep it running while I tune? The cam is a TSP 224R 114LSA.

The engine is an LQ4, PCM is from a 2002 fbody and the tune is MOSTLY that. MAF table from LQ4.

Tune VE first, then MAF, then idle?

thanks for the help

[WS6FirebirdTA00]

Yes, to get by for now you can check out the idle trims and add some air, maybe bump up the idle. Then once you get the MAF and VE close set it where you want.

[jakeb]

awesome, thanks

I assume for idle trims you mean "Idle Airflow" in the base running airflow

[WS6FirebirdTA00]

Yes.