Im out of ideas. Please help ID my O2 problem

[wcj]

Im out of ideas.

Ive swapped injectors. Swapped O2 sensors. Swapped O2 sensors between banks. Swapped battery. Can anyone give me an idea what is causing my bank 1 O2 to spaz out like this? It does this even when I swap sensors.

As you can see, when it freaks out, it causes the car to run pig rich on that side.

15620

[Wheelz]

If its not tracking with any sensors or injectors it could be wiring.. Which isn't going to be easy to debug

[ddnspider]

It looks like your wideband pid is also tracking a goofy A/F and bouncing around so the narrow band may actually be correct for that bank. Have you gone open loop and logged your A/F with the wideband?

[joecar]

HO2S11:
to the right of your cursor it looks like HO2S11 sees too much fuel...
what happens if you swap injectors across banks...?

What DTC's do you have...?

[wcj]

Have not tested in OL.

Hey Joe, Nothing changes when I swap injectors. I pulled my FAST36 injectors and replaced them with stock Z06 injectors (adjusted BIN) and the O2 still freaks out. I get no DTCs...

The car does run normal at times so this problem is sporadic.

15621

Do you think a weak exhaust valve spring could cause this? Maybe a vacuum leak on the driver-side of the intake manifold? When the O2 freaks out, the bank1 injector duty cycle does increase so the computer is dumping fuel when this happens.

[joecar]

If it was an airleak on bank1, then O2 sensor would see extra air and voltage would peg low...

but, O2 sensor is pegging high, meaning that it sees less air on that bank (more fuel, or clogged header primary/secondary).


Check injector sub-harness, it might be crimped or chaffed (allowing it to sometimes short to ground, firing several injectors).

[joecar]

But... that is really weird, why is IBPW1 is running so much higher than IBPW2...


can you also log LTFT's.

[wcj]

Ltft is disabled.

Clogged cat? Even if I have an x-pipe? That wouldn't cause the computer to adjust bank1 injectors, would it?

[joecar]

Ltft is disabled.

Clogged cat? Even if I have an x-pipe? That wouldn't cause the computer to adjust bank1 injectors, would it?
No, forget the clogged cat, that was before I decided that this was weird :)


Are STFT enabled...?

[wcj]

Yeah. I can try to log some STFTs. May take me a few days to get to it since summer's been crazy. Would it help if I attached the previous logged file? Dont think this could be valve-train related? Bad PCM?

[joecar]

Yes, please attach most recent log.


Depends on what the STFT show...

valvetrain or PCM may or may not be a possibility

( and thinking about it again, clogged cat may enter the picture again )

[wcj]

Attaching the log file from last night.

No STFT on this one but I'll add it to my pids and log that in the next day or two.

15622

[joecar]

That log shows that the PCM is biasing the O2 switch points differently across banks:

O2BIAS11 = 642 mV
O2BIAS21 = 482 mV


take a look at table B4105, post a pic of it here.

[wcj]

I have both banks set to 450 mv.

15623

[joecar]

Hmmm... the PCM thinks the O2's are switching at different points...

[joecar]

Can you disconnect both O2's and capture a log (showing HO2S11, HO2S21, O2BIAS11, O2BIAS21).

[wcj]

Sure. Should I disable dtc's?

[wcj]

My VE table looks a bit off but nothing else looks weird to me.

15625

[joecar]

Sure. Should I disable dtc's?No.


My VE table looks a bit off but nothing else looks weird to me.

15625See in this log (with O2's disconnected) that the O2 voltages are within 450+/-20 mV...

so this points to the problem being that the harness has a possible short to power (0.6-0.7 V) or the PCM has failed.

[wcj]

So it should not be reading 450 +/-20 mV? You mentioned it's possibly a short to power so it's not a ground problem then? I guess the easiest thing for me to check is the PCM if I have one available. Just need to reflash the PCM with my current OS/tune, correct?

[joecar]

I'm inclined to think it's a PCM problem...

but when you disconnect the PCM, see if you can test for short to power/ground just in case (wiggle the harness around).



Yes, do full flash of your OS/calibration... then use scantool to write your VIN... then use tunetool to do VAT relink (if necessary).

[wcj]

When you say test for short to ground, are you suggesting wiggling the harness at the PCM or at the sensor or both? Also, would this be done while scanning with the engine off but the key in the ON position?

[ddnspider]

When you say test for short to ground, are you suggesting wiggling the harness at the PCM or at the sensor or both? Also, would this be done while scanning with the engine off but the key in the ON position?

I would recommend you disconnecting the battery before doing this and do a continuity test :good:

[wcj]

I would recommend you disconnecting the battery before doing this and do a continuity test :good:

Gotcha

[joecar]

When you say test for short to ground, are you suggesting wiggling the harness at the PCM or at the sensor or both? Also, would this be done while scanning with the engine off but the key in the ON position?Yes, the harness at both ends and everywhere in the middle.

You also wiggle the wires at the PCM connector... pull the connector apart and inspect the pin crimps.

No, this would be done with battery disconnected as dnns said...

you set your DMM to ohms/audible, you clip the leads to small paper clips (unless you have a terminal probe kit), and you connect to each end of the harness to test for continuity...

you repeat this on all the O2 wires...

then you connect one end of the DMM to vehicle power cable and test each of the O2 wires...

then you connect that end of the DMM to vehicle ground and test each of the O2 wires...

then for sanity check you place the DMM across each vehicle ground to make sure they have no resistance...

then you pick some other pins and check for cross-shorting...

and so on.

[5.7ute]

Also ensure you check & clean the earth points on the cylinder heads.

[wcj]

Finally got to check for continuity and it checked out good. I guess the next thing to check is the pcm.

[Wheelz]

I just want to note, and it still may not be this, but even if it passes a continuity check (and I don't know how extensive you checked) you still could have

A) a loose connector that vibrations from a running engine may cause it to loose contact from time to time.

B) a soft short, ie two wires have rubbed due to vehicle vibrations and can make contact, even though when stationary and off they are not touching. (IE ground and signal, or even signal to chassis, pulling the signal low momentarily giving a false reading)

Like i said earlier, I don't know how you performed the continuity test but hopefully you checked each wire to itself, and then verified it has no path through any other wire, source, or ground. Depending on your time and resources, I personally wouldn't pay for a new ECM first, but I would try almost all other alternatives before going to the extreme of yanking the harness out for inspection. You may have to visually inspect the wires to find a failure. If you could swap a loaner ECM in for a few days that may tell you a lot. Honestly though, I really think your ECM is fine and you have an issue with the o2 sensor wiring.

I just remembered a bug I tracked down with an amplifier that was a weak ground point. It worked fine for 6 months, even passed a continuity check the day I found the failure, but over time the connection corroded so that under load a voltage developed across the ground lug and would actually shut the amp off. I finally found it by measuring the voltages at the amp with it all running as the volume was turned up. I'm only throwing that out there to give you ideas of ways to check for issues.

[joecar]

+1 what Wheelz said...

( including measuring voltage drop across connections )

[wcj]

I think instead of trying to chase it, I may just re-pin my harness with Bank 1 Sensor 2. My rear sensors are tuned out so if there was some sort of short in Sensor 1 harness, maybe it is isolated to just Sensor 1.

Any reason I couldnt/shouldnt swap 25/26 and 68/69 and run my front O2 that way?

[Wheelz]

The only thing Im not sure of is whether or not you'll have to use the actual front o2 sensor, which would mean you might have to swap connectors on the sensor too.

I don't know how the harness is ran, but are your rear o2 sensors hooked up now? I know they are tuned out. I've just been thinking it is too coincidental when you disconnected the front o2 sensor that the voltage hovered at 450 mV. In the back of my mind I keep wondering if the signal wire from the rear o2 sensor is making contact with the front o2 signal wire. If they are hooked up you could try a run without them to maybe save you some trouble.

If they aren't hooked up now I don't see how repining the connector won't be beneficial.

[wcj]

The rear sensors are not in the car and the connectors are just hanging there. Im going to re-pin and swap connectors to see if that fixes the problem.

[wcj]

Repinning front and back on bank 1 didnt seems to work. The connector and pins are different and using a Camaro front o2 sensor didnt seem to register for some reason2

I swapped and repinned bank1 sensor 1 with bank2 sensor 1 and did some logging and at least was able to confirm the PCM isnt bad. Swapping the pins on bank1 with bank2 resulted in the log showing bank2 having the problem now which makes sense since my bank2 is actually reading drom the driverside (bank1).

[Wheelz]

Is it possible to buy replacement pins so you can still use the rear harness, but replace the pins on it? Then use your front o2 sensor

Just thinking out loud

[wcj]

Is it possible to buy replacement pins so you can still use the rear harness, but replace the pins on it? Then use your front o2 sensor

Just thinking out loud

I could. The easiest thing to do would probably be replacing the plug on the sensor to match the rear sensor harness plug. I tested bank1 sensor1 for continuity and they checked out fine. I checked them for a ground short too and did not find one. I'll check pins 29 & 69 against the other wires in the harness to make sure there's no short tomorrow (maybe). Im starting to think this may be mechanical, like an intake leak along bank1 causing the o2 to read lean.

After I cross check the wires and swap to AC Delco sensors (I currently have Bosch) if it is still messed up, I may see about picking up a cheap LS2 intake to see if that changes anything. Maybe I have one of those hard to track down 102 problems.

[EagleMark]

I swapped and repinned bank1 sensor 1 with bank2 sensor 1 and did some logging and at least was able to confirm the PCM isnt bad. Swapping the pins on bank1 with bank2 resulted in the log showing bank2 having the problem now which makes sense since my bank2 is actually reading drom the driverside (bank1).So re-pinning moved the problem from bank to bank? Doesn't that indicate the issue is in wiring?

[Wheelz]

And I thought the car was reading rich which implied it was getting less air than it calculated, which is opposite what a leaky intake would do.

By this point, you might try just running new signal wires to the ECM. I don't know of another way to eliminate the wiring by this point

[wcj]

And I thought the car was reading rich which implied it was getting less air than it calculated, which is opposite what a leaky intake would do.

By this point, you might try just running new signal wires to the ECM. I don't know of another way to eliminate the wiring by this point

The car is running rich according to my wb and bank1 injectors dump fuel when the O2 starts acting up which leads me to believe bank1 O2 is reading lean.

I probably should just run new signal wires. Probably could have figured it out by now if I did.

[Wheelz]

The car is running rich according to my wb and bank1 injectors dump fuel when the O2 starts acting up which leads me to believe bank1 O2 is reading lean.

I probably should just run new signal wires. Probably could have figured it out by now if I did.

According to the NB it's reading lean when it's not actually lean or the wideband wouldn't show it's going too rich. If you had an air leak your wideband would register lean and the NB trims would pull it back to stoich, then when the leak is stopped it would be rich till the fuel trims re-adjusted for the non leaky intake.

Unless my logic is flawed, I don't think you can have an air leak based on your logs.

I feel your pain on this one. Wiring is no fun to troubleshoot

[joecar]

...

I swapped and repinned bank1 sensor 1 with bank2 sensor 1 and did some logging and at least was able to confirm the PCM isnt bad. Swapping the pins on bank1 with bank2 resulted in the log showing bank2 having the problem now which makes sense since my bank2 is actually reading drom the driverside (bank1).

When you run like that (banks swapped), what happens if you physically swap NBO2's across banks (but keep the banks swapped)...?


Sounds like the pins in connector are making faulty contact (i.e. more than zero ohms).

[joecar]

According to the NB it's reading lean when it's not actually lean or the wideband wouldn't show it's going too rich. If you had an air leak your wideband would register lean and the NB trims would pull it back to stoich, then when the leak is stopped it would be rich till the fuel trims re-adjusted for the non leaky intake.

Unless my logic is flawed, I don't think you can have an air leak based on your logs.

I feel your pain on this one. Wiring is no fun to troubleshootYes, his first pic shows NBO2 voltage trending high/rich and IBPW adding fuel, this messes with our minds.


Thinking Out Loud (TOL):
If it was a misfire, the NBO2 would show a low/lean voltage (since NBO2 sensor sees oxygen content), and this is not what is shown in his pic.


+1 wiring problems are difficult.

[wcj]

Well, no better way to test if the rewiring of my bank1 O2 fixed the problem than a 2 hr 30 mile commute this morning.

Electrical problems are just weird I guess. Nothing I tested would repro the problem but a new harness and I can drive for 2 hrs in stop and go traffic with the AC on without a hiccup.

Thanks for all the help.

[joecar]

Cool :cheers: glad you got it sorted out.


Does your old harness show signs of damage...?

[wcj]

Im just glad to confirm it wasnt my incompetent tune that's caused this problem. Joe, I think this may be related/cause of the stalling/idling problem you tried to help me with in May 2012.

To tell you the truth, I didnt bother pulling the old harness. Didnt want to try to figure out the logistics of getting the old wires out so I opted to just run a new harness for B1S1 from plug to terminals (hi/low PCM, GND, + Fuse). Since the terminals in the PCM had to be pulled and was replaced with the new terminals from the new harness, I just clipped and soldered the new GND and + wires back into the factory fuse and GND locations.

[Wheelz]

Congrats! Nice to know you found it

[wcj]

Congrats! Nice to know you found it

and all it took was 5 pages of updates and 45 days to do what you posted in Post #2! :mrgreen:

[Wheelz]

and all it took was 5 pages of updates and 45 days to do what you posted in Post #2! :mrgreen:

We all are lucky on occasion!!