Odd O2 Voltage Problem

[95ImpySS]

I spent the entire day trouble shooting an odd O2 voltage issue. My tuner noticed that the voltage for bank 1 (Left/Drivers Side) is lazy and inconsistent. I have installed 2 brand new AC Delco oxygen sensors and swapped them from either side. The problem stays on Bank 1. Upon initial start both O2s read almost identical 0.455v’ish. As the engine warms up Bank 1 start’s to fall off as Bank 2 starts to increase. If I blip the throttle, they both shoot up over .600 volts. Towards the end of the short data logs I made I noticed that Bank 1 has a slightly lower voltage off idle than Bank 2. At idle bank one will read 0.032v’ish. But as soon as you blip the throttle it shoots up.

I have changed the harness connector twice. Swapped the o2s around, and tried a set of Denso O2s. All create the same problem. I am %99 sure there are no exhaust leaks. Only difference between Bank 2 and Bank 1 is Bank 1 has a new connector soldered and heat shrinked on. Shielded with silicone coated fiberglass heat shield. Both Bank 1 and Bank 2 O2 wires read 0,2-0.3 ohms back to the PCM. Spark plugs look good. Not too rich, not too lean. Engine is an 11:1, 355 LT1, with LE2 heads, LE custom grind Hyd roller (224/230 .573/.568 110 LSA), 32lbhr Bosh III injectors, Long tube headers, X pipe dumping before rear axle. No Cats, Smog pump, EGR.

I can email them to whoever is interested in looking at them. Shoot me a PM or an email at LT1Garage@gmail.com

EDIT:
Here is the Datamaster file: http://www.freefilehosting.net/copyofrun1
Here is the FreeScan File: http://www.freefilehosting.net/runone

Anyone have any Ideas WTF?

Thanks in advance

[firebird_1995]

You got split Blm's too? I had the exact same issue with one bank having lazy voltage at idle. But I also had an injector fault code 18. I changed all my injector pigtails and adjusted my idle down on the TB to allow the iac to supply more of the idle air and it went away.

[Tyler Wheat]

Shot in the dark here, but I would try to solder that break in your O2 wire really well. Those things read at such a low level, any little bit can throw them out of wack. Worst case scenario, you get another connector and re-do after that has been ruled out.

EDIT/ I suck at reading comprehension apparently. If its soldered, I dunno. Sounds like you are having an issue in closed loop if they are identical at start-up. Sorry I'm no help on this. WTF is most certainly correct in this case. Wish I could help you.

[95ImpySS]

You got split Blm's too? I had the exact same issue with one bank having lazy voltage at idle. But I also had an injector fault code 18. I changed all my injector pigtails and adjusted my idle down on the TB to allow the iac to supply more of the idle air and it went away.

I spent last Saturday modifying my POS BBK throttle body to get the IAC counts right. Finally got IAC counts right. I have no codes thrown pertaining to O2's or fueling. The tuner has BLM's locket at 128. The tune I'm running is the base line.

Thanks for replying!

Shot in the dark here, but I would try to solder that break in your O2 wire really well. Those things read at such a low level, any little bit can throw them out of wack. Worst case scenario, you get another connector and re-do after that has been ruled out.

EDIT/ I suck at reading comprehension apparently. If its soldered, I dunno. Sounds like you are having an issue in closed loop if they are identical at start-up. Sorry I'm no help on this. WTF is most certainly correct in this case. Wish I could help you.

I appreciate the reply. They are soldered pretty well and heat shrinked in marine heat shrink. After changing the connector, nothing has changed. Another thing I noticed is that there is no real change during open or closed loop. Both O2's only read the same or close (+or-0.100mv during the first 15-30 seconds of running.)

[firebird_1995]

What are you idling at? I wonder if the overlap in the cam timing is causing it. I think I raised my idle to 900 in the process when I went through this. Maybe it helped.

Edit: I suppose you would see problems on both sides if the scavenging effect was causing the issue. My last stab at this would be; is there a possibility the rocker arm adjustment is off or a lifter is a little lazy at low rpms?

[95ImpySS]

What are you idling at? I wonder if the overlap in the cam timing is causing it. I think I raised my idle to 900 in the process when I went through this. Maybe it helped.

Edit: I suppose you would see problems on both sides if the scavenging effect was causing the issue. My last stab at this would be; is there a possibility the rocker arm adjustment is off or a lifter is a little lazy at low rpms?


The cam is not crazy. But somewhat large. The idle is set to 850rpm hot idling in park/neutral. I tried a hand full of other tunes. All did the same thing. I redid valve lash a few times after finally hunting down failed plug wires. Lash is set with the engine running method. Car runs great after its warmed up. Throttle is quite snappy. don't know what the issue is at this point. Has me baffled. Curse of the LT1's I have to assume. :shiner:

[firebird_1995]

Sorry man...
What does a blm locker do anyways?

[97firehawk]

a guy i no was having his car tuned and he had a bad o2 and didn't no it and there was no time to get a new one he has always had problems with lazy o2s and so have i anyway the tuner said no big deal and he just tuned them out he now has no o2 sensors and his car is an animal and it huffs nitrous im not sure if this method is the best way or not but i figured id mention it.


also i no this doesn't really help the problem but i figured if all elts fails this could be an option.




is the o2 sensor seating properly to the bung no leaks there

[79LT1Monte]

If it only does it at idle I would look for a vacuum leak on that side of the intake. Try spraying carb cleaner around any potential leaks while watching O2 voltage for a spike. Vacuum will be highest at idle, so it will show up more on your data.
Also check the voltage at the sensor with a volt meter for yourself, if your O2 sensor is reading correctly but the scanner or pcm are interpreting it wrong you will end up chasing your tail.

[95ImpySS]

Thanks for the reply's everyone.

BLM Locker locks the BLM's at 128 so the PCM dosen't change fueling according to what the O2's say.

I thought about tuning out the O2's, but with the money I have spent on this build. I really want Everything to work :)

I will check for vacuum leaks this evening. Can I check the O2 voltage with it disconnected and engine running? Or do I have to tap into the wiring?

EDIT: I have added links to the Datalog files in post one.

POST 1: http://ltxtech.com/forums/showthread.php?18916-Odd-O2-Voltage-Problem&p=230081&viewfull=1#post230081

[95ImpySS]

Well firebird_1995 you were close. It was a combustion problem.

Problem solved. After shooting each primary with my IR temp gun. I noticed that cyl number 5 wasn’t firing. Took my stethoscope to the injector and found it wasn’t firing. Went to disconnect the injector plug and the damn 12v+ wire fell out. Soldered on a new plug and BAM. Car runs much better and no more uneven O2 readings. Odd thing is the car ran like a top when it warmed up. I always figured the hesitation was tune related since it changed with heat.

Thanks for the replies. Getting ready for a test drive :)

[firebird_1995]

awesome man. glad to hear you got it fixed. those injector wires are all pulled tight and brittle from the heat and old age. how did it run?

[95ImpySS]

Runs pretty good. Took it out front and did a weak burnout. Car sounds awesome. Damn upgraded brakes moved much more bias to the rear.

http://www.youtube.com/watch?v=98Vkpq3JtAg